Friday, April 30, 2010

Microphones and Accessories


One cannot make an audio recording without a microphone. It's that simple. For stereo, you need two identical microphones. You also may need more than that for highlights and ancillary ensembles such as vocal choruses and soloists. 

Ask any ten recording engineers what microphone techniques they favor, and you'll get at least thirty answers. Everyone has their favorites, many are variations on the same ones, some might seem downright bizarre. But they must work, or they wouldn't be mentioned. When we get to that part of the discussion, I will tell you my favorites and explain all of the basic ones. Microphone placement is an art, an art that is learned through experience. But before you can fly, you have to walk, so we will start with microphone types suitable for recording.

Microphone Types

There are two basic types of microphones used in recording today, the condenser mike and the dynamic mike. Years ago, amateur recordists used several other types. One type was called a piezoelectric mike, often referred to as a crystal or ceramic mike and the fourth type of microphone that recordists used to use was the carbon-button mike, ubiquitous in the 40's, 50's and even the 60's neither of these latter types are used any more. 

Dynamic Mikes

Of the types of mikes used today, probably the easiest to understand is the dynamic mike. These microphones work by moving a membrane connected to a coil of wire in a magnetic field - like a loudspeaker in reverse. The sound strikes the membrane (or diaphragm) which causes it to vibrate in sympathy with the sound striking it. This causes the coil of wire to move with it. The coil, cutting across the lines of force set-up by a permanent magnet, induces a minute electric current to flow through the coil wire. This current is analogous to the sound waves striking the diaphragm. This current is amplified and can then be sent to a public address system or to a recording medium. Dynamics of this kind are often used as PA mikes or vocalist mikes. They are valued for their ruggedness and dependability and simplicity. 

A variation of this principle is called a ribbon mike. Instead of a diaphragm and coil, the ribbon mike uses a long, thin ribbon of some lightweight foil. The ribbon is usually folded like an accordion to get more surface area. The ribbon is suspended between the poles of a very powerful magnet. When the ribbon vibrates in reaction to being hit by sound waves, it, again, cuts across the lines of magnetic force and a weak current flows along the ribbon. Both ends of the ribbon element are connected to a transformer which steps up the tiny voltage created by this current flow and matches the ribbon's impedance (which is extremely low, usually less than an Ohm) to the microphone cable and amplifying circuit. Ribbons have such feeble output that they require a lot of amplification before they are useful. Even so, throughout most of the history of commercial broadcasting, ribbons were the preferred microphone for most radio stations. The RCA 44BX microphone, which is usually the mental image most people conjure-up when they think of a microphone, is, in fact, a ribbon mike.


The famous RCA 44BX. For almost two decades this mike was the voice or both radio and television broadcasting and most recording done here in the United States. To many people, this is what they think of when someone says the word "microphone". 


Ribbons are almost always bi-directional and pick up sound equally from both the front and the back. Due to the thinness of the ribbon, they are easily damaged by blowing into them or using them out of doors on a blustery day. While ribbons like those from Royer can be made with outstandingly flat frequency response (and concurrently high prices), most ribbons don't have a lot of top end. They are good for instruments with lots of midrange such as choruses and perhaps acoustic guitars. They are often valued for their very natural, warm sound and make beautiful announcer mikes (as long as the announcer doesn't blow into them).

Condenser or Capacitor Microphones 

Probably the most often used microphone for recording is the condenser or capacitor mike, as they are sometimes called. These mikes have always offered the highest performance and most accurate translation of sound to electrical current of any microphone technology. Although, condenser mikes have been around almost as long as has radio broadcasting and "electric" recording, really good ones, of the type we now associate with the technology, didn't appear until WWII Germany.

The Germans had developed two technologies during that war that absolutely dumbfounded the espionage types in England and other Allied listening posts. German radio stations would be broadcasting concerts of, say, the Dresden State Symphony Orchestra on nights when the Allies knew for a fact that Dresden (or Berlin, or Cologne, or Munich) was, at that moment. under heavy air attack. Two other characteristics of those "phantom" broadcasts puzzled the Allied listeners: The concerts were broadcast without breaks, tics and pops, and without the "scratchy" sound that usually accompanied transcription by phonograph record. The then only known method of recording sound for later broadcast. Add to that the fact that the recordings sounded so life-like and clear; they must be live!  It wasn't until after the war, when the Allies occupied Germany and went into their radio stations did they find the answer to this puzzle. The Germans had perfected the audio tape recorder, which, due to several German innovations (like AC bias for recording) turned out recordings that were unparalleled in their wide frequency response, low distortion and noise. The second thing they found was that the research arm of the German broadcasting ministry, Telefunken, in collaboration with the Georg Neumann company, had perfected the condenser microphone. Georg Neumann, another condenser mike pioneer,  had actually invented the modern condenser mike in the early 1930s. Called the Neumann "Bottle" it was used throughout Germany and developed all during the war. In 1947, Neumann came out with the famous U47 (also sold under the Telefunken name), which, along with the later U87 became the ubiquitous form factors for condenser Mikes. So much so, that most condenser mikes today, irrespective of what they cost or where they are made, look like one or the other.

After WWII, both Telefunken (Left) and Neumann (right) came out with the first successful condenser mikes for recording, the U47. Here in the USA, they unseated the RCA 44BX as the microphone of choice for recording and broadcasting, ushering-in the era of high-fidelity - just in time for FM broadcasting and the LP. 

Operation

The condenser mike works in one of two ways. Both types work because the diaphragm and the back plate of the microphone element form a small capacitor of about 40-50 picofarad. In the most common application, this capacitor is charged with a polarizing voltage which is used to control an amplifying device such as the grid of a tube, the base of a bipolar transistor or the gate of an FET. The sound striking the diaphragm varies the capacitance of the mike capsule coupling more or less voltage to the control element of the amplifying device causing that device to conduct either more or less and the resultant signal is analogous to the sound striking the diaphragm. The second method uses a similar capacitor to the above example, but instead of that capacitor controlling the coupling of voltage to the microphone circuitry, this second method has the capacitor as part of a tuned RF oscillator circuit. The audio, striking the diaphragm, changes the frequency of the oscillator, also as an analog of the sound being picked-up. At the output of the microphone, a detector circuit called a discriminator strips the RF frequency from the signal leaving only the audio modulation. This works a lot like an FM radio, and indeed,  is often called an FM microphone. While there are still some FM microphones being made, most condenser mikes are of the first type.


The biggest drawback to the condenser mike has always been it's requirement for an external power supply to polarize the capacitor mike capsule and to drive the electronics. Pre-solid-state, most condenser mikes relied upon dedicated power supplies and special cables with multi-pin connectors to connect the mike to the supply. These cables had to carry both the audio and the various voltages such as the B+ and filament voltage for the tube(s) as well as the polarizing voltage for the capsule. Generally speaking, the link from the power supply to the recording console was via standard XLR cables. Extension cables between the mike and power supply were non-standard and usually quite expensive. After condenser mikes became solid-state, in the late 1960's, the separate power supply was abandoned in favor of so-called phantom power. Phantom powering uses 48 volts (this came from the telephone industry) DC which is piggy-backed on the same wires that carry the audio from the microphone to the mixing console. The DC doesn't affect the audio and today, most mixers have the 48 volt phantom-powering power supply built in. More expensive mixers allow you to apply the phantom-power individually to each microphone input, while cheaper mixers merely allow one to turn it on or off globally to all microphone input circuits. 


The Electret Condenser Microphone


In the late 1960's after solid-state electronics became possible inside the microphone itself, the need for tubes and the high-voltages they require was obviated. This allowed practical application of a type of condenser microphone capsule called an electret. An electret is a stable dielectric material with a permanently embedded static electric charge. Due to the high electrical resistance and chemical stability of the materials used, the electret device will retain it's charge for hundreds of years. Although the electret principle was discovered in the 1920's, it didn't become practical until two Bell Labs engineers designed one using a thin Teflon coated metal foil as the electret in 1962. The combination of the two maturing technologies, the materials technology for the electret itself, and the use of the FET transisitor for the amplifier, suddenly made this kind of microphone practical. Due to the fact that an electret condenser microphone does not need a polarizing voltage, and the FET amplifier in the mike draws very little current, suddenly, small, cheap condenser mikes which ran on batteries became possible. The biggest application for these mikes, became, of course, in telephones to replace the century-old carbon button mike. The improvement in voice quality was apparent to everyone who heard one of the new electret miked phones.


Schematic of a typical Electret Condenser Microphone showing how simple it is. Often, these mikes can be powered by a single watch battery yet provide long battery life and better performance than the cheap carbon, crystal, or dynamic mikes that they have replaced. 





 It wasn't long before companies like Sony, in Japan, were applying electret principles to recording microphones. In the early 1970's, Sony introduced the ECM-22p a professional quality electret that could be powered by either a nine-volt battery or via standard 48-volt phantom-powering. The ECM-22p sported rugged build quality, and surprisingly decent frequency response. Sony spec'd the mike at 40-15,000 Hz, but I've found that the two that I owned to be rather bass-shy. However they are great on the top end and midrange and make excellent drum mikes. After having owned them for almost 30 years, I can say that they still work as well today as the did when new (although the Eveready #206 9V batteries are somewhat hard to come by these days - thank Sony for making them standard phantom-power compatible).


Early pro electret condenser Microphone the cardioid Sony ECM-22P

Although a number of electret microphones for pro use have been made, most are small-capsule mikes designed for the low-end consumer market. When I was in Japan a number of years ago, I picked up a Sony electret single-point stereo mike (ECM-929) to use with my Walkman-Pro cassette recorder. This mike has been excellent with it's M-S pick-up pattern and adjustable soundstage width. But like most electrets, it's tiny capsules make it a bit shy on bass and definitely suited only for casual recording (see the second installment of this blog for a picture of this microphone photographed with a Sony MiniDisc recorder).  


Modern Condenser Microphones

For most of the post-war era, condenser microphones were considered the Rolls-Royce of microphones. They cost a bundle. Even today, A Neumann condenser mike like an M149 can easily cost close to $6000! When I was in the recording business in the 1970's I owned a pair of "cheap" Japanese condenser microphones from Sony called C-37Ps. These had an FET amplifier in them and a single capsule that was switchable between omni-directional (non-directional) and cardioid (uni-directional). They cost well over $1000 in 1975 dollars and were considered inexpensive compared to Neumann, AKG, and Beyer condenser mikes of the time. 

Sony C-37P FET Condenser Microphones were considered "inexpensive" at about $500 each in the mid 1970's. They are still very good microphones, by the way and command top-dollar when they show up on the used market. 

Enter the Chinese

From 1949 until the death of Chairman Mao Tse-Tung, China was a closed country. They did not trade with the west, and, essentially, had no consumer markets as existed in the west. Like the Russians, the Chinese reverse-engineered (read that "copied") essential technologies from western manufacturers and simply made their own. One of these technologies was microphones. All the best condenser mikes had "Chinese copies" and they were used in both broadcasting and recording. When the Bamboo Curtain fell in the 1980's, it was found that these copies of Neumanns, AKGs, Telefunkens, Scheops, Sennheisers, Beyers et al, were actually not half bad, and available for mere pennies on the dollar compared to their western counterparts. 

As soon as trade agreements with western companies became possible, many people decided to have their own microphone designs built in China. That brings us to the present glut of excellent and cheap condenser microphones which not only are well made, but actually perform very well. It is possible to buy Chinese-built microphones from firms such as Avantone, Behringer, Samson, Rode, and many others. 

Most of these mikes are better than the classic mikes from which they are copied. The reason is that the classic Neumann and Telefunken models (not to mention AKG and Beyer) had acid-etched brass diaphragms, which, while thin and light by the standards of their day, are today, so massive that they gave these microphones a peaky, rising top end which can sound harsh, especially when used to record digitally. Modern condenser microphones, including Chinese ones, have diaphragms made from a thin Mylar plastic which has been "sputtered" with an atom-thick coating of either aluminum or even gold. The metal coating on the Mylar makes the diaphragm a conducting capacitor plate without adding any weight. The resulting diaphragm is so low in mass that it's fundamental resonance (the characteristic that gives the older mikes such an aggressive top-end) is pushed way up into the ultrasonic region of the audio spectrum, where people cannot hear it. Modern mikes, even inexpensive ones, therefore tend to have a smooth, clean sound that shames most older designs. 

One Chinese made mike that I have used and found to be just about the best mike I've ever used  is the Avantone CK-40. This stereo mike has switchable patterns between omni-directional, figure-of-eight, and cardioid and is actually two microphones in one case. The top element can be rotated either left or right 90 degrees (for a total of 180 degrees relative to the lower element). Physically, it is a close "copy" of the famous (and fabulously expensive) Telefunken ELA-M-270 from the 1950's which is still made and can still be purchased new from Telefunken USA for a mere $16,000. The CK-40, on the other hand lists for about $600 and instead of being tubed like the Telefunken, features an ultra-quiet FET preamp. 


The Avantone CK-40 (right) can be said to be a virtual "Chinese copy" of the famous Telefunken ELA-M-270 (left shown without its shock mount). Having used both an original ELA-M-270 and the CK-40, I can tell you that while both microphones are good, the Avantone is much better and, in fact, is one of the best sounding microphones this writer has ever heard.


Choosing Microphones for Your Own Recording Set-up


There are a number of characteristics that one needs to keep in mind when choosing microphones for recording. Generally speaking, the larger the capsule diameter, the better the bass. Most decent condenser mikes, these days have at least a 1-inch capsule and I would consider this a minimum for any mike that will be used for general coverage of an orchestra, symphonic band, or any ensemble with a wide range of instruments needing a solid low-end foundation. Affordable microphones that meet this criteria are, happily, fairly abundant. The Samson CO1 at around $80 is an excellent entry into this type of so-called "big-capsule" microphone as is the SM-ProAudio MC01. Both of these cardioid-only microphones are excellent performers and superb values. For multi pattern mikes, the $150 Samson CL8 is a very good pick and offers a choice of cardioid, figure-of-eight, and omnidirectional patterns. Also in this range is the excellent Behringer B-2Pro. All of these mikes have excellent, wide frequency response and solid bass performance. Of course, I cannot heap too much praise on the aforementioned Avantone CK-40 stereo mike. This dual-head single-point stereo mike has large 35mm diameter capsules and among the best low-end performance that I have heard. When coupled with this mike's smooth midrange, clean, flat top-end and wide dynamic range. it's hard to beat - at any price.


Behringer B-2Pro multi-pattern, large capsule condenser microphone shown with included accessories

There are always going to be situations where you are going to need more than just a single stereo-pair of microphones to get proper coverage of the ensemble you are recording. When recording a jazz big-band recently, I found that the stereo pair was not picking up enough of the piano. Listening to the ensemble play from the audience perspective, I could hear the piano, but when listening to the mike feed on headphones I could not. This necessitated the use of an auxiliary microphone on the piano and mixing the result into the overall pick-up from the stereo-pair. To do this I used a single cardioid SM-ProAudio MC01. This mike was placed low so that it just "peaked" over the edge of the grand piano and was aimed at the center of the raised top. I pan-potted the mike to the extreme left (the piano was on the extreme left side of the band) and raised the level on the mixer input so that the piano could just be heard in the headphones. The results were perfect.

This means that you are going to need more than just one pair of microphones. It is not necessary that these mikes have the bottom end of the main mikes as they are usually just for accent. Sometimes there will be vocalists involved and these mikes will work fine for that as well. A typical microphone complement for a modest amateur recording "kit" might be:
1- Avantone CK-40 single-point stereo mike (or equivalent such as a pair of Behringer B2 Pros on a 'T-bar'.
2- Behringer B2 Pro multi-pattern microphones (or equivalent switchable pattern mikes).
2- Samson CO1 cardioid large capsule microphones or M-ProAudio MC01(or equivalent)
2- (a matched  pair) of "lipstick" small capsule microphones (Behringer C-2, C-4 or equivalent)

 
Author's Microphone complement for location recording. Each mike has proved itself to be rugged, well made, and a good performer. 

Needed Accessories

Missing in the above pictures are two very important components. The first is microphone cable. Since you never know where you are going to end-up, it is important to always have enough. My rule of thumb is to carry 4 -50' lengths, and eight 25' lengths. This looks like a lot, but I'd rather carry too much than too little. It is rare that you'll ever need more than three or four microphones for any one gig, but you never know what you might run into or how far away from your microphones that you'll be setting-up. 

Cables

Now, about cable. Naturally, it needs to be balanced microphone cable with decent quality XLR connectors; a male on one end and a female on the other. Other than that, if you buy from a reputable source such as Shure or Hosa, you can be assured of getting decent quality. Let me clear something up about cables right now. I spent years in the aerospace industry as a wiring/cable engineer for some of our country's most leading edge rockets and satellites. I have studied wire thoroughly and I can tell you this, just between you and me: at audio frequencies, wire is wire. Oh, I know, you can spend a fortune on cables from high-end audio cable companies, but it's all bling; stuff and nonsense. No double-blind cable test has ever revealed any difference whatsoever between expensive and cheap cables. Audio cables have no sound of their own. So buy well made, reliable cables from reputable sources and don't worry about the rest. One thing is important, however, and that is to use runs as short as possible and keep the number of connectors between the console and the microphones as low as possible. In other words, one long cable is better than two or three shorter ones connected together. 

Mike Stands

Now you need something to set the mikes on. Floor stands are fairly cheap, and the best kind for location recording are the folding kind. I use four of the Euroboom OS13 stands. These microphone stands have a folding, three legged base and a column which raises to about 63" and a boom that gives another 33" of extension. They weigh only about 5 pounds each, fold very compactly and can be bought online for about $30 each. For the big (and heavy) stereo mike, I use either a Euroboom with sandbags on the legs (for stability) or I use the foldable StuBoom from On-Stage ($120). This stand extends to 80" and the counterweighted boom gives another 82" of extension. This stand is heavy, and large. I only use it where I have the room for it and I don't carry the boom very often because it won't fit in my car very comfortably (being almost 7 ' long). But it is there when I need it. Check around, you can find some very decent mike stands out there. If you have a music store in your area, you might ask them to be on the lookout for used stands for you. I once bought a huge studio boom with a cast iron base for $20 at a local music store. New ones are almost $300 today. I ended up giving it away because I couldn't easily carry it around. Deals are out there.

Next time we'll talk about microphone pick-up patterns and how to mike various instruments for best effect.









Sunday, April 25, 2010

Microphone Mixing and Pre-amp Options

This time we are going to discuss how to get the microphone signal to the recording device. For this discussion, we are going to assume a two-channel stereo recording, but, keep in mind that these things apply to multi-channel recordings as well (whether they are mixed to two-channels for production or to 5.1 channels or any other surround-sound format.)

Professional quality microphones, whether condenser, or dynamic have one parameter in common: they all need to be amplified before they can produce a recordable signal. Usually, microphones need between 40dB (100X amplification) and 60dB (1000X amplification) to get their signals up to what is regarded as "line level" which is required to give maximum record volume. Some microphones, such as ribbon mikes have such low output that sometimes as much as 70 or even 80dB of gain is required. This means that pre-amps required for microphones must have the following characteristics: They must be quiet, have low distortion, lots of headroom and wide, flat frequency response. They also must have differential inputs to take professional "balanced" microphone cables.

Noise, is a major factor here. At these levels of amplification, the "self noise" generated by active components such as bipolar transistors, FETs,  Integrated Circuit (IC) operational-amplifiers (op-amps) and vacuum tubes becomes a major factor in the quality of the finished recording. Much of this self-noise is thermal. Active electronic components use the physics of electron attraction and repulsion to move signals around and to amplify them. Moving electrons through the devices creates a certain amount of random, or non-correlated noise (along with heat). In fact, vacuum tubes (or valves as they are sometimes called) operate by heating an element inside the tube hot enough to actually "boil" electrons off of its surface. The rest of the tube's elements (the grid(s)) control the flow of those electrons and actually determine how many of those boiled electrons get passed it and on to the plate where they constitute the amount of current that the tube conducts; I.E., less current flow represents small signals, more current flow represents larger signals. Since all of the tube's amplifying ability comes from the fact that it is a heat-operated device, the amount of random electron flow, and thus noise, is characteristically quite high.

Solid state devices work differently, and while they still create heat it is much less than a tube, and rather than the heat being the method of operation for these devices, it's more of a by-product with them. While noise is still an issue, generally speaking, solid-state electronics are much quieter than tubes. Does this mean that tubed electronics cannot be used to make modern digital recordings? Not at all. The reason is because there is another way to get voltage amplification of a microphone signal; transformers. Voltage gain, in a transformer, is largely a matter of the turns ratio of the transformer's coils between the "input" (the primary coil) side of the transformer and the "output" side (the secondary coil). As an example, if you put 10 turns on the primary windings (coil) of a transformer, and 100 turns on that transformer's secondary windings and apply a one-volt AC signal to the primary, you will get about 10 volts out of the secondary. This is an oversimplification, but it does show how the voltage gain of a transformer is determined by it's turns ratio. Since the transformer is not an active component, it adds no noise, but it will amplify any noise in the signal applied to it right along with that signal. There is no free lunch, after all. So if we take the output of a good mike with decent noise characteristics, feed it into a transformer before applying it to an active microphone preamp, it is possible to get by with far less gain in the preamp itself. Less gain equals less thermal noise being added to the signal making it very feasible to use tubes in modern microphone preamps and still get signal-to-noise ratios that are compatible with even high-resolution digital recordings. Of course, there is a downside with transformers. Good ones, which have flat frequency response across the entire audio spectrum are expensive. Transformers also have problems with maintaining phase integrity at all frequencies and especially have problems coupling low frequencies through them. Most modern solid-state microphone pre-amps and mixers don't use transformers, but use a type of input circuitry called a differential amplifier. These are very good at rejecting noise that is common to both legs of the balanced interconnects from the microphones. These include, hum, air conditioning spikes (when the compressor cycles), noise created by the proximity of light dimmers in auditoriums and other public venues, etc. This ability is called common-mode rejection.

These days, a decent microphone preamp will give signal to noise ratios of somewhere in the region of  about -125 to -130dB, the greater the number, the quieter. Any microphone preamp with figures in this region will give recordings that are, for all intents and purposes, essentially silent. Even with the playback gain set quite high, one should hear nothing but blackness when no instruments are playing. 

Another characteristic of microphone preamps to consider is headroom. Live music can get quite loud. Cheap preamps can clip (distort) when fed a microphone level that's too high. Modern condenser mikes can handle sound pressure levels of as much as 150dB before clipping. It would seem like it would be nice to have a microphone preamp that had similar characteristics. Thankfully this isn't necessary. All microphone inputs have controls on them to vary the amplifier's gain and most have a light on them to indicate when that mike channel is clipping. A rule of thumb here is that the louder the source is playing. the less gain is required from the pre-amp. It is always advisable to ask the ensemble's leader to have them play the loudest part of their program before the recording starts so that you can advance the gain to clipping, and then back-off until the clipping indicator light goes out for all microphones. Then, back-off a bit more - just in case somebody wasn't really playing their loudest. This insures the highest possible signal-to-noise ratio without worry of overdriving the microphone preamps. Some recording engineers use a calibration box on each input to feed a signal of known amplitude into each microphone preamp. This might work in a studio situation where things like room-loading and individual microphone characteristics are well known, but for location recordings, I'd rely on the actual musicians to tell me how loud they're going to play rather than count on some unrelated "standard". After all, conditions will vary from venue to venue and musical group to musical group. No two situations will ever be the same. Of course, if you are in a position to record the same group in the same venue time after time, experience will guide you in setting your microphone preamp gain. Ultimately, the amount of overload protection built-into one's microphone preamps is down to their design. The higher the power supply voltage feeding the amplifiers, the more head-room they will have. On modern mixers, even fairly inexpensive ones, this shouldn't be a problem.

EQ

Many mixers contain, for each input, a group of controls called "EQ" or equalization controls. These are essentially, "tone controls". Usually there are at least three and sometimes more. They are usually marked "high", "mid" and "low". Sometimes the frequency at which they come into effect is also marked on the mixer and sometimes that frequency has its own control and can be varied somewhat. There is usually a set of these for each input on the mixer. If one is doing an 8 or a 16-track recording where the mix will be finalized at a later date and every instrument or instrument group has been assigned it's own microphone channel, then I can see where such controls would be very useful. On the other hand, most of the types of mixers that are used for location recording are "X" number of channels in but only two channels out and are designed for mixing on-the-fly while the performance being captured is actually occurring. So, no matter how many mikes you are using, the end result is two channels recorded to media, and that is cast in stone. There is no going back and "tweaking" this mike feed or that one. Since there is no way to "undo" an injudiciously applied amount of EQ in these cases, I tend not to use it. The exception would be if I had a certain microphone that was deficient in some way (like a ribbon mike that had little response above about 10 KHz) I might use a bit of EQ on that channel to accentuate the area that was a little lacking. It is also possible to judiciously add a little presence to a vocalist by lifting the midrange a bit, or to reduce the chestiness in a male vocalist's voice by reducing the bass on his mike's input. Other than that, I feel that it's best to leave these controls out of the picture. They're great to have when you need them as long as you keep in mind that a little goes a long way, and the results are not reversible.   

Each microphone mixer or pre-amp has its own features such as built-in reverb effects, or busses for external effects and it is beyond the scope of this article to discuss them. But what I do think is necessary is to talk about the size of mixer needed for location recording. 

When I got back into recording after a long hiatus (see the first installment of this blog entitled "Commercial Recording Quality"), I figured that since all of my earlier recordings had been made with mostly two microphones, and when confronted with a chorus as well as an orchestra, a maximum of four, that a four microphone input mixer would more than suffice.

Behringer 1202 Mixer sports four excellent microphone inputs and 8 line-level inputs. These can be had for less than $120

When I bought the above pictured Behringer 1202, I was astonished by the street price of just a hair over $100 (US). My previous mixer, a TAPCO, had cost about $1200 and wasn't anywhere near as good. Behringer calls their microphone preamps in this line of mixers "Xenyx" pre-amps and they tout them as being very quiet. They are. I have made some astonishing recordings with this mixer. The circuitry sounds so good and is so quiet that instruments just "appear" out of a velvet black background. I realize that manufacturing this mixer in China (from a German design) is part of the reason for the low-cost, and the advancements in solid-state technology is responsible for the rest, but still, I was blown away by the quality. Soon I realized, however, that the types of recordings that I was doing required more than just four microphone inputs. Not the least reason was because I was using a stereo microphone in the M-S pattern (which will be discussed in another installment), and that required three microphone preamps to yield two channels. That left one. Realizing that I needed more microphone inputs, I went back to the Behringer catalogue and found the 1832FX. This mixer sported 6 microphone inputs as well as built-in reverb effects. I hesitated due to the size of this mixer (one more thing to carry). It is much larger than my 1202. But I figured that where the 4-input 1202 was sufficient, I could cary that, and where I needed more, I could carry the 1832FX. 



The Behringer 1832FX Mixer has 6 of Behringer's excellent "Xenyx" series microphone pre-amps and 8 line level inputs. It also sports built-in digital special effects and a graphic equalizer on the outputs. The street price on this mixer is around $250.  

While I have chosen Behringer mixers, that doesn't mean that there aren't others just as good, and while I find the Behringers excellent performers and suburb values, Mixers from Peavy, Mackie, Allen & Heath,   Edirol and Yamaha are probably just as good. Choose according your projected needs and keep in mind that you will have to tote around whatever mixer that you eventually choose. If you do find, at some point down the road, that you need more microphone channels than your current mixer can provide, that there is another alternative to buying a whole new mixer.

Add-On Microphone Preamps

Most mixers on the market today come equipped with a certain number of microphone preamp stages. In the case of the Behringer 1202, that number is four, and with the 1832FX it's six. The Peavy PV20, for instance, is close in price to the Behringer 1832FX and offers sixteen microphone stages but lacks the Behringer's comprehensive features list.  It is also immense. Many of these same mixers also have a number of line-level inputs. While these, lacking the gain, are not designed for microphones, but rather for other sources such as recorders (for mixing-in pre-recorded material and adding to it), and even other mixers. My Behringer 1202 and 1832FX both have 8 such inputs and other mixers may have similar. This is a perfect application for outboard microphone pre-amps. These devices can be had for as little as about $35 for a single-channel tubed unit from Behringer up to several thousand dollars. SM Pro Audio sells an excellent 4-channel solid-state microphone pre-amp called the Q-Pre4 which is available for a street price of less than $80. For my purposes, the Behringer, again, proved to have the most bang for the buck. Behringer's MIC100 is a solid-state, stand-alone, single-channel microphone preamp with a tube output buffer to impart "the tube sound" to the microphone being fed it. The 12AX7 vacuum tube used is not for gain and therefore adds no appreciable noise. You will, of course, need one for each extra microphone you connect. For either Behringer mixer, that means eight in total. I carry two in my recording kit and have even used them in place of an entire mixer when only two channels are required! They sound excellent and would, in fact, constitute a fine starter system. A pair of MC100s, a pair of decent big-capsule cardioid condenser mikes such as the Samson C01 at less than $80 each (street price) or a pair of Behringer Pro 2Cs (multi-pattern mikes) at slightly more along with a Zoom H2 solid-state recorder and you will be recording 24-bit, 96KHz stereo recordings for a a maximum investment of only about $500! This kind of price/performance combo would have been unheard of just a few short years ago.

The Behringer MIC100 Tube buffered Microphone preamp. At $35 street, it's excellent and hard to beat for flexibility and control


The SM Pro Q-Pro4 4-channel Microphone preamp. at around $80, it would be hard to go wrong having one of these in one's kit


Next time we'll discuss Microphone types and how to deploy them...



Tuesday, April 13, 2010

Recording Devices

For most of the "stereo era" the choice of recording mediums to use was limited to one and only one, magnetic tape. When the digital age came upon us, it was still limited to only one choice, magnetic tape, although this time it was video tape in the form of U-Matic, VHS or Beta and other digital magnetic tape formats such as DAT. Professional studios even used large reel-to-reel digital tape decks, some with 2-inch wide tape. But for most of the years following the Second World War, it was analog tape running at 15 or even 30 ips (inches per second) with wide tracks taking up fully half the width of the tape (1/2 of a quarter-inch-wide tape for each of two channels or three tracks covering a piece of 1/2 -inch tape or 35 mm magnetic "film") to guarantee reasonable signal-to-noise ratios and relative freedom from dropouts. The machines were big, heavy, complex and expensive, but that was all we had.

Today, it's quite different. The choices available to even the amateur recordist are so varied as to be almost bewildering. Digital recording has benefitted from the advances in computer technology which is moving at a breakneck speed. The first casualty of the computer age was the practice of recording digital audio to magnetic tape. Computer hard drives became the norm for studios who gladly replaced their stands of multitrack digital tape recorders with racks of computer hard drives. These are used for both audio capture and for long-term storage (with suitable back-ups, of course). Now, solid-state memory is making inroads into the hard-drive-based recording camp. Solid-state memories have the advantages that they have no moving parts, have long storage life and can be physically very small. Expect this trend to continue until it has replaced hard disk recording altogether.

Example of a rack-mounted Solid State Recorder/playe


As amateur recordists, we benefit from these computer-based innovations in a number of ways. There are portable devices available which use a myriad of formats and media that cover just about everything from MP3 recording from a live source, all the way to the very sophisticated and flexible DSD (Direct Stream Digital) with it's 2.8 or 5.6 MHz sampling rate. The equipment required ranges from laptop computers to tiny solid state recorders, some, not much bigger than a pack of cigarettes. Let's examine some of the more popular and accessible options:

Using a Computer as a Digital Recorder


Since most people have a laptop computer of some description laying around, this would seem to be the cheapest and easiest path to digital recording. Certainly, the software to do this is in abundance, and one of the better programs, Audacity, (http://audacity.sourceforge.net/download/) is even free. Available for Windows, Mac, and Linux, this program gives you all the tools you need, save one, to use your computer as a digital recorder. The one tool missing is an outboard analog-to-digital converter. It takes analog signals in from the mixer or microphone preamps and outputs a digital signal in the required format. It needs to communicate with the software on the computer, and for this the interface between computer and A/D converter needs to be via a two-way bus such as USB or Firewire. All modern computers have USB 2.0, but few use Firewire. Unfortunately, the current USB standard, USB 2.0, is bandwidth limited and even two channels of 24-bit, 96 KHz digital audio is a stretch. While USB is fine for 44.1 and 48 KHz digital audio, even at 24-bit, it's just too slow for the higher sampling rates. Some implementations of USB use "tricks" to defeat the master-slave protocol on USB to allow it to work at 24-bit, 96 KHz, but the conversion is slow, causing a delay between the capture and the digitization of the audio stream. This delay is called latency and it makes monitoring the digital signal very difficult because it can be many seconds behind the performance being recorded. Therefore, for anything greater than a 48 KHz sampling rate, it is advisable to use Firewire. Firewire 400 is faster than USB 2.0 in the continuous transfer mode because it is a peer-to-peer protocol that doesn't have the computer overhead of USB. This reduces latency and even allows for the transfer of two-channels of digital audio at 32-bit, floating point and 192KHz sampling rate.

However, the problem remains that most computers don't come with Firewire ports. If you use a desktop computer, you can always purchase a Firewire PC card to go in it, but if you are doing location recording (as opposed to having your own studio), this makes the prospect of live recording about as appealing as the days of lugging huge reel-to-reel analog recorders around. Laptops are the preferred computer here, but these days, only a couple of Sony models and Macbook Pros have Firewire ports built-in. Some of the more expensive Windows Laptops sport PCI Express slots and these allow one to add third-party Firewire support to one's laptop, but either buying a Macbook Pro laptop or a higher-end Windows laptop with a peripheral card slot is an expensive proposition, and there are other alternatives.

Also, the outboard A/D converter can be expensive but at least here there are excellent inexpensive solutions, available as well. For A/D (and D/A) conversion of so-called "CD quality" recordings (16-bit, 44.1 KHz sampling rate), there are a number of USB interfaced converters available from companies like Behringer, Lexicon and Samson, some for less than (US) $40. Behringer sells an excellent Firewire computer interface box that has A/D and D/A converters, called the FCA202 that will accommodate up to 24-bit, 96 KHz audio for less than (US) $100 street price. I have used this converter with an iBook laptop and Audacity to make some truly spectacular sounding recordings.

Behringer FCA202 Firewire combination A/D and D/A computer interface
 is excellent quality and affordable with street prices less than $100


Hi-Md

For years, Sony has sold its proprietary "Atrac" compression scheme in conjunction with its "Mini-Disc" transport and media system for portable recording and playback. While "Atrac" arguably sounds somewhat better than MP3, it's certainly not what most of us would use to "master" live performances. About 7 or 8 years ago, Sony came up with an improvement to the format called Hi-Md. The improvements were threefold. First, the Hi-Md disc capacity was increased to 1 Gigabyte. This gave just short of 8 hours of Atrac recording and playback at the highest 256 kbps "Hi-SP" Atrac3+ setting. Secondly, Sony improved it's compression algorithms to "Atrac3+" which was a distinct improvement in sound quality, and thirdly and most importantly for our purposes, Sony added a linear (non-compressed) 16-bit, 44.1Khz PCM recording ability to the format which gave 1 hr and 34 minutes of CD quality audio on one Hi-Md disc! These devices can make excellent recordings, but there is one drawback. If you didn't buy the top-of-the-line recorder/player, there was no way to physically transfer the resultant digital recording from the Hi-Md recorder to one's computer! All you could do was to output it as an analog signal and re-digitize it (in real time) as you write it to your computer's hard drive.

The Sony Walkman MZ RH-910 Hi-Md MiniDisc recorder/player shown here 
with an M-S electret condenser microphone

Solid State Recorders

In the last five years, a new type of portable recorder has appeared. Taking their cue from digital cameras, these small, hand-held recorders use the same kinds of solid-state memories as cameras use to store the digital audio files. Lacking moving parts of any kind, these devices give excellent battery life and with tiny SD cards, are truly hand held. Most have their own microphones built-in, but will take external mikes. Some, like the Zoom H4 series, will take professional XLR microphone connectors and will even supply the 48-volt phantom power required by professional condenser microphones. Others will take only consumer grade outboard electret microphones connected via 1/8-inch "mini" phone plugs. All will accept line-level inputs from mixers and outboard microphone preamps, but most accept only consumer audio levels of -10 dBm. Many of these devices offer multiple recording formats ranging all the way from MP3 to 24-bit, 96 KHz PCM audio. But a lot of these recorders only record to 48 KHz, so one must be careful when buying. One of the smallest and most affordable of these devices is the Zoom H2 "Handy-Recorder". Capable of recording up to 24/96, this device sports four microphones of it's own and can be used to record surround sound (although it is limited to 48 Khz sampling in this mode). At a street price of less of than US $200, one could use this device with an inexpensive mixer from Mackie or Alesis or Behringer and a couple of inexpensive big-capsule cardioid condenser microphones as one's primary recording system without any apologies to anyone. An even simpler system would be Zoom's H4n which has it's own microphone preamps and powered XLR connectors. Then all you need is the microphones. Of course, you'd then limit yourself to only two, but the recorded results would be virtually identical to those obtained with the H2 and an outboard two-microphone preamplifier or mixer as the recording circuitry for the two units is identical.  

I use an H2 as a backup recorder and it has come in handy on several occasions. I just connect it to my mixer with a stereo mini-phone plug to stereo RCA cable, and start it before the program begins and forget it. If anything goes wrong with the computer setup, I still have a 24-bit, 96 Khz recording. 

These recorders are made by such companies as Alesis, Sony, TASCAM, Samson/Zoom, Korg, Marantz, Edirol, and M-Audio. 


The Zoom H2 "Handy-Recorder" is capable of making 
high-resolution recordings at 24-bit/96 KHz



Mixers With Built-in Recording Devices

An alternative to a separate Mixer or microphone preamp and recording device would be a solution that combine the two into one unit. Some, like the Korg D888, use and internal hard disk to store audio directly. Others, like TASCAM's 2488neo, use both a hard drive and a CD burner internal to the unit. The downside of both of these units is that one is limited to 44.1 KHz sampling rate, although the TASCAM will record 24-bit to the hard drive. Zoom's new R16 will will act as 16 track stand-alone mixer and has 8 microphone preamps. It records to solid-state memory, or can function as a DAW interface to a computer using USB which limits its sampling rate to 48 KHz. While these can be effective at reducing clutter and simplifying one's setup, I find that they are restricting in that one cannot upgrade any part of the system (let's say that down the road, you find that you need more microphone inputs, for instance) without replacing everything.


Zoom R16. An Example of an "all-in-one" solution. 8-microphone inputs,
built-in recorder to SD Cards up to 32 Gig, Limited to 24-bit, 48 Khz. 

The Ultimate Recording Medium, DSD

Back around the turn of this century, Sony, responding to complaints from audiophiles that CD wasn't "good enough" came out with a new high-end format called "Super Audio Compact Disc" or SACD. The format used for recording these high-resolution discs was a departure from all other recording schemes then in existence. It was called DSD or "Direct Stream Digital" and instead of being the standard Pulse Code Modulation (PCM) used for CD and DVD-A (another high-resolution format), DSD used a single-bit process that employed a very high sampling rate of either 2.8 MHz or 5.6 MHz. SACD didn't succeed in the mass market, as most people felt that regular CD was "good enough", but it does have a following in the audiophile market and companies like Telarc, Mobile Fidelity, Virgin Records, and a number of others still record and release in this format. Korg, known for their recording and sound reinforcement equipment, sells three recorders that will allow the amateur recordist to capture performances in this ultimate of high-resolution formats. The three machines are called the MR-1, which is a small hand held field recorder about the size of a Zoom H2 (see above) the MR-1000 which is a larger field recorder about the size of a very thick paperback novel, and sports XLR microphone inputs,  and the rack-mounted MR-2000. The MR-1 retails for about (US) $900, while the MR-1 retails for about (US) $1500 and the MR-2000 is about (US) $2000. 

It is possible to regularly find MR-1s on E-Bay for less than $500 and I got mine for $299. Now, the DSD format and Korg's implementation of it needs a little explaining. Currently, there is no practical way for any home or amateur recording enthusiasts to make their own SACD discs. While there is software available for this, it is extremely expensive, the cheapest being around (US) $5000. However, the software that Korg supplies with their DSD recorders, called 'AudioGate', allows owners of Windows and Mac computers to "translate" the super high quality DSD master to any currently used digital audio format. This means everything from 24-bit, 192 KHz PCM all the way down to MP3. Think of the DSD format as the audio equivalent of the "Raw" format for digital cameras. One can store these DSD files on any hard disk and then transfer them to the MR-1 for playback in their native format, or make lower resolution copies to distribute to your "talent" (those who allow you to record them) or even to burn DVD-A's at 192, 176.4,  96 or 88.2 KHz sampling rates. 

This is my preferred method of recording. The device is beautifully made, takes pro levels, has balanced line inputs and will transfer files over USB to one's computer. A couple of slight drawbacks of this device need to be noted here. One is that it uses an internal 20 Gigabyte hard drive. This makes the recorder somewhat fragile and it means that one cannot increase storage size. The built-in battery is also limited to about 2.5 hours of recording time and is not user replaceable. For my part, battery life is a non issue, because I always record in venues with electric mains power (after all the mixer needs mains power too). Also, unlike the MR-1's bigger siblings, it records at only 2.8 MHz, 5.6 MHz not being available on this unit. That's OK really as I have heard SACDs with samples recorded at both sample rates, and honestly, I defy anyone to hear the difference. Most commercial SACDs are mastered at 2.8 MHz. 

I prefer the Korg DSD recorder to my old method of using my computer as a recording device because the MR-1 is so much simpler to use than the computer (which is actually, quite complex in it's setup). Forget to do any one of a number of "rituals" with the computer, and you might find yourself, as I did fairly recently, recording a large symphonic band with the computer's little built-in voice microphone instead of with the fine stereo mike that was on the stand in front of the group. OOPs! Luckily, I had the Zoom H2 connected to the mixer and it did record the ensemble properly. Always have a backup, if possible. 



The Korg MR-1 can record in DSD, or PCM and is very flexible. 
It will make the highest quality recordings to
 which an amateur recordist can currently aspire 
and it's smaller and lighter than a laptop; simpler too! 


Next time we'll look at mixing and microphone preamp options.



Sunday, April 11, 2010

Commercial Recording Quality

I don't know if any of my fellow audiophiles out there have noticed this, but even the best recordings always seem to "lack" something. Uncompressed digital (even RedBook*), promises wide dynamic range, excellent frequency response and low distortion. It should be possible to make recordings so good that, given a halfway decent playback system, the musicians are in the room with you. It is technically possible and surprisingly easy to do this, but it rarely happens with commercial recordings. Why is it that still, in this digital age, audiophiles cling to performances recorded more than fifty years ago as the pinnacle of the recording arts? Recordings made in the late 1950's and early 1960's by such people as Mercury Record's C. Robert Fine, or RCA Victor's Lewis Leyton in the classical recording world, and Rudy Van Gelder of Riverside, and Impulse fame in the world of jazz are held in such high esteem, that even CD and SACD re-releases of their recordings still sell very well today. It's as if no progress has been made in the art and science of recording in the last 55 years or so.

I have found in building my stereo system that this has become a dog chasing his tail endeavor. My playback equipment gets better and better and yet the recordings to which I listen, ranging from terrible to OK never get any better than just OK. Even so-called audiophile recordings from labels such as Telarc and Reference and Naxos, to name a few, never sound quite as good as I think they should.

This started me on a quest. If I can't buy reference quality performances to play on my high-end audio system, perhaps I could make some. I didn't come to this decision in a vacuum. In a previous life, I was a semi-pro recording engineer who used to record a major symphony orchestra for their archives and for broadcast. I had also professionally recorded, for broadcast on NPR's "Jazz Alive" series, such artists as Hubert Laws, Dizzy Gillespie, Stepan Grapelli, etc. Needless to say, in most cases, I kept masters of these recordings. The client either received copies or co-masters recorded on a tandem analog recorder. I gave up this pursuit because of the weight and amount (not to mention the cost) of the recording gear that I was forced to schlep around, necessary, in those days, to make a truly professional recording. But, still, today, CD transfers of these 25-year old 15 ips 1/2-track stereo analog tapes are among the best sounding recordings I have.

Things have changed. Today, excellent quality recording equipment is not only plentiful, but cheap. It is possible to buy excellent mixers for just a few hundred dollars. Recoding devices capable of 24-bit, 96 KHz performance are likewise very inexpensive. It is even possible to purchase small, portable recording devices that will actually capture audio in Direct Stream Digital (DSD), the 1-bit recording method used for SACD. And this equipment is small and light. One can easily carry an entire recording studio (less the microphone stands, of course) on the passenger seat of the family car! The mike stands go in the trunk, of course.

On the microphone side of things, changes are even more profound. When I was recording semi-professionally, good quality condenser microphones were available from only a hand-full of suppliers such as Neumann, Sony, AKG and Telefunken and they were extremely expensive (especially the Neumanns and Telefunkens). Today, an excellent pair of big-capsule condenser mikes can be had from dozens of sellers for just few hundred dollars (Neumanns and Telefunkens are still tres cher, however). Companies such as Behringer, Audio Technica, Avantone, and Rode make microphones that have flat frequency response, low distortion and low noise. Today's microphone capsules use sputtered gold coated Mylar diaphragms which have such low mass that they move the microphone's fundamental resonance far above the audio passband. Back in the 1970's and 1980's most good mikes still used acid-etched brass diaphragms with frequency response peaks starting at around 6 or 7 KHz and peaking at 16 or so KHz. This worked OK with analog recording where magnetic tape self-erasure tended to roll-off the upper frequency extreme anyway, but when digital came along, it made for unnaturally bright and brittle-sounding CDs. This is, I believe, mostly where CD got it's bad reputation from audiophiles early-on.

In future posts I will discuss some of these issues and make recommendations for a really good starter recording set-up. One that can be easily carried from place to place and yet will yield recordings that sound so much better than anything you can buy, that it will make you wonder what the pros are doing wrong! We will also discuss how to get local groups (whatever your musical preference) to allow you to record them. We will also discuss various microphone techniques, and how to choose the best arrangement for the individual ensembles you will encounter.

We will also discuss playback equipment, of course. After all, this a two-ended process; capture and playback. Getting the most from good recordings requires a good stereo system. I think that we are going to have fun with this blog and I invite comments, suggestions and submissions from everyone.

*RedBook - the standard 16-bit, 44.1 KHz CD format.