Chapter 5 MICROPHONES AND TECHNIQUES (Why Your Home Recordings Sound Like Home Recordings!) There are a lot of people in the world today who know what a microphone is. This is probably because we have become a society which has become very "at home" with personal tape recorders. But, the vast majority of these people do not have the vaguest idea of how to use a microphone correctly, much less the differences of microphone types. I have experienced (suffered?) many amateur tape recorder operators who are completely content so long as the microphone they are using is located anywhere within the same room with them. In fact I've met some individuals who didn't even know, or believe, that a microphone was needed to make a tape recorder record their voice! If you look around a bit you will observe many people sitting in a large group using a portable tape recorder to record a play or a speech. They will get a recording of the room sounds, but not much clarity of the primary subject. I 'spose I will have to admit that some of todays recorders do a "heck" of a good job under those conditions, but even so, the recorded results won't be acceptable for any purpose other than aiding the recall of the observer who did the recording. But, more on this subject later. For now, let's briefly discuss microphone types and concepts. In case anyone didn't know it, sounds are mechanical pressure variations (vibrations) of the air. When these air pressure vibrations strike our ear drum diaphragms they are set into motion. This resulting motion is sensed by nerves and sent to our brain (man's internal computer) and we say that we hear. A microphone operates somewhat like our ear drums and nerves. That is, sound pressure strikes a moveable diaphragm within the microphone and the motion of the diaphragm is sensed to produce an electrical signal. The electrical signals which are produced are quite small in most applications, and the size of the signal (voltage) is proportional to the loudness of the sound. The direction of electrical current flow of the signal (polarity) is a function of the sound pressure either increasing (+) or decreasing (-). These electrical signals are then amplified (made bigger) and processed to shape tones or loudness, then they are used to create magnetic recordings, modulate a transmitted carrier to be broadcast, etc. Microphones, being mechanical tools, are "dumb" devices. They simply react to pressures which happen to strike them, and they do not react to all sounds from all directions the same. How well a microphone hears all sound pitches, and from which directions, is a function of it's style and quality. For instance, most inexpensive recorders come with microphones for which no performance claims are made. In contrast, expensive professional grade recorders virtually never come with microphones because the manufacturers realize that you will want to select one which is best suited to your needs and applications to obtain quality performance. Also, make no mistake here, microphones also exhibit tonal "personalities" of their own so recording engineers often have personal preferences for specific sound characteristics of them. Although there are many different microphone types, there are really only two which enjoy widespread use today. These are the "Dynamic" and the "Condenser" types. The Dynamic type uses a diaphragm that moves a coil relative to a magnet (much like a speaker) to produce electrical signals. The condenser type (sometimes called "capacitor") does not generate an electrical signal as does the dynamic type. A condenser microphone changes an internal electrical signal by virtue of the diaphragm plates motion relative to another internal plate, the two of which form a capacitor. The dynamic type is mechanically fairly rugged. That doesn't mean you should "bang" on it, drop it, or throw it around - but if you inadvertently do those things it probably will continue to function "O.K.", however, it's tonal quality and/or sensitivity may be permanently changed. On the other hand, condenser microphones won't tolerate rough mechanical treatment. The condenser diaphragm is thin, light, and fairly tightly stretched. There usually are electronic circuits inside the microphone head as well. These characteristics generally make a condenser microphone fairly expensive, although a few good ones can be obtained for $100.00 or so. Since condenser microphones have light weight diaphragms which need to move only very small amounts, they tend to be superior for picking up high pitched sounds. However, this is a two-faced blessing. A condenser microphone used by a person who lacks knowledge of it's idiosyncrasies will frequently get too much high frequency "brightness". Sibilant sounds (S's) will be exaggerated and distorted. All in all, I would advise you that condenser microphones are "great" - but in general you are far better off to avoid them and stick to good quality dynamic types. Dynamic microphones really are the "workhorse" of the industry. Stick with the good brand names such as AKG, EV, Shure, etc., and expect to pay between $100.00 to $200.00 each for them. You probably won't get a much better price than the lowest, but you certainly can exceed the higher, but shouldn't have to. Microphones come in basically two styles of "hearing". There are omni-directional (all directions), and there are cardioid (one direction) listening patterns. This characteristic is referred to as the micro-phone's "polar pattern". A true omni-directional microphone picks up everything around it. For the best general applications they can't hardly be beaten. Unfortunately, too often we have to make sound pickups in environments whose ambient background sounds are not controlled or very desirable, in which case the "wide open" pickup pattern of these microphones is a definite problem for you. Therefore, unless you have really good sound isolated studio rooms, or else if you really do want to hear the typists, visitors, and air-conditioning blowers in the background on your recordings and broadcasts (I doubt that you do!) then plan on using cardioid type microphones. Cardioid microphones, in theory, hear sounds only arriving into the frontal axis of their diaphragm. In fact, they do pick up sounds from the sides and rear but these are greatly reduced, especially the higher pitched sounds. This brings up an important point regarding the uses of cardioid microphones. Don't get more than about 30 to 40 degrees off of the front of the microphone if you wish to preserve full fidelity and sensitivity. The high frequencies drop off very rapidly as you exceed 30# off of the frontal axis. Another interesting characteristic of most cardioid microphones is what is termed "proximity effect". This is a tendency for the microphone to sound very bassy or "boomy" when it is used very close to the sound source (close talked). You have probably observed this during someone's use of a "public address" sound system when they moved up very close to the microphone and they seemed to become unusually "heavy" sounding and louder. This can be advantageous when calling a meeting to order, but usually is not desirable for natural sounding recordings. Therefore, you should attempt to use cardioid microphones a few feet away from the speaker, yet pointed straight at them. Also, never use more than two people on a single cardioid microphone, because at least one, if not more, of them will always be too far "off mike" to the sides. OK, I can begin to sense the raised eyebrows and "grunts" of disapproval around me. I know that most of us don't fully follow these prescribed rules of cardioid microphone use. Most of us use them very close and often mounted nearly 90. to the side of the operators mouth. We do this because our studio environments are so defective we are forced to close talk them, and then, when we get too close to the front surface of the microphone, we often pick up breathing, wind noises, "popping p's", etc., so we place the microphone off to the side. This is unquestionably bad practice and should be avoided, however, we sometimes must cheat a bit to be the most successful with what we have to work with. Let me caution you that such close talking techni#ue also presents you with another new problem, namely poor and inconsistant volume levels. You see, if you double the distance between the speakers mouth and the microphone, the volume picked up will decrease as a function of the inverse of the distance squared that is to say, it would become #th. Thus, if the microphone is about two inches from the speakers mouth, and they should move their head, the distance can quickly become eight inches or so. This would cause a volume level decrease of about 12 decibels, which psychologically would generally seem to be one half to one third as loud. Just as importantly, this head movement also causes a significant shift in the voice fidelity as picked up by the microphone which further increases the impression of loss of volume. The lesson is simply this, if you must use cardioid microphones close talked like this, then either fix your rooms so you can get the microphones back at least a foot or two, or else purchase some quality headband type microphones (such as the Beyer DT-109's, etc.) for these kinds of operations. You will recall that we previously discussed that professional grade recording or broadcasting systems used inputs and outputs that were specified to be 600 ohm balanced lines. Likewise, quality professional microphones should be balanced line-type rated at 150 or 200 ohms. Many "general purpose" microphones are floating around the country which are unbalanced line types rated as "High #". These are fine for less serious uses, but do not employ them in your studios as they are susceptable to "hum" and other electrical noise pickup, and they have poor frequency response if the connecting cables approach or exceed about ten feet, which they surely will in the typical studio applications. By the way, a microphone should always be connected into an amplifier whose input rating is about ten times that of the microphone in order for the microphone to sound natural and correct. This suggests that your console microphone preamplifiers should provide about 1500 to 2000 ohms load to the microphone. By the way, these low # (150 to 200 ohm) balanced line microphones can be used with cable lengths of at least 100 ft or more. Try not to get "carried away" with this, but you don't have to be too fearful either. Many Radio Talking Book operations make use of volunteer persons to produce recordings. Often, the more competent of these volunteers are allowed to do their tape recordings at their homes. Everything we have discussed about the need for quiet sound controlled studio rooms and correct microphone application, still applies, but how do you accomplish comparable recording quality in the typical residential home? The answer is, of course, that you can't. You can, however, get fairly acceptable results even in an untreated residential environment if you take some care and effort and if you understand why home tape recordings sound like home tape recordings. Nearly everyone who has ever used a "home" tape recorder has at one time wondered why their results of recording some live event were so disappointing in sound quality. It seems that somehow, what they heard at the time of the event just didn't get heard well by the recorder. Some people will simply accept such poor results with little concern, partially because they tend to listen only to their own voice on the recording and completely ignore all of the background sounds and noises which are also present. You often see this form of behavior when you show someone a photograph of some subject which just also happens to include that person. Often the viewer never even notices the real subject of the photograph because their attention is focused upon themselves. So it sometimes is too with audio reproductions. Still other people hear bad sound recordings and accept them because they simply assume that this is what you will have to expect unless you use special "professional" equipment. But there is only just a little truth in this. And finally, some people upon hearing that poor live event recording will wonder why and what they could do to sound more professional without having to become one. It is this last group of people I hope we can move you into. What we all would hope to achieve from a tape recording is a quality which is called "presence". Presence means exactly what you would imagine it does - the feeling of being present at the place and time of the recording of the event. So, why is it that "home recordings" so often lack this "presence" even though everything sounded really pretty good to you while you were doing the recording? Well, it has to do with computers. Not the ones made by IBM, etc., but the computer nature built into our heads, and the equipment manufacturers could not provide inside your tape recorders. When sounds arrive at you, they generally will reach one ear slightly before the other. We call this time, or phase, delay. Also, the sounds are slightly louder in one ear than the other, termed amplitude difference. Our brain, which is natures best of all computers, can readily distinquish those sounds we want to listen to from those sounds which we wish to ignore by use of the phase and amplitude difference characteristics. Therefore, when we are in a crowded room such as a church, or a bar, we usually have little difficulty hearing conversations we want to hear, unless they happen to be too weak. However, if you were to place a microphone at your location during this event and record the conversations, you would find that upon playback of the tape recording, the room noises would be so distracting that the desired conversations would be virtually unintelligible and covered up by extraneous sounds that you didn't even hear at the time. Why does it sound so much worse on the tape recording? Because when the sounds are captured by the microphone and then replayed over a speaker which is a singular source of sound, the phase and amplitude difference information that our brains computed on during the actual live event are no longer present. Therefore, we can no longer separate out those sounds which we don't want to hear, and the result is mostly confused noises. This means we can't make good usable recordings outside of a studio environment, right? Wrong! The secret is to recognize and consider what engineers would call signal-to-noise ratio. If the ratio of the desired sound signal to the undesired sound noises is great enough we can still mostly ignore the undesired sounds. We all realize that any sound is loudest at it's source and decreases in volume according to the inverse square law. (Actually this is too simplistic a statement since in acoustics there are many factors of near field, far field, ambient effects, frequency dependent absorptions, etc. But even so, generally, this is true psychoacoustically.) Thus it is obvious that we should attempt to place our microphone as close as possible to the desired sound source, while at the same time get as far away as possible from undesired sounds. Of course, any tricks available to reject the pickup of the undesired sounds such as barriers and/or cardioid microphone use helps a great amount. Naturally, it also helps if the person whose voice you are recording will speak loudly too! Incidentally, if you are doing your tape recording on a machine which has an automatic volume level control feature, be sure to turn it off and use the lowest possible manual volume control setting you can, consistant with getting correct recording levels. Again, don't forget that if using this close talked cardioid microphone technique, you must be wary of the problems we discussed earlier such as breath and wind sounds, sibilance, popping p's, proximity effects, and volume level variations. If you are attempting to do tape recordings "at home" instead of in your studios, you must consider, and exclude, as many of the normal room sounds as possible. The recording location should be chosen to be where it is as quiet as possible and removed from obvious sounds such as aircraft flying by, telephones ringing, sirens screaming past, loud talking, childrens laughter and crying, dogs barking, fans running, clocks ticking and chiming, birds chirping, etc. Believe it or not I've heard all of these sounds and more on such "done at home" tape recordings. Some people recording at home in the summertime have been known to sit by an open window so as to enjoy the fresh air, with the result being that they managed to record virtually all of those listed background sounds. Needless to say, I hope, don't do this! Once on the tape, such background sounds are impossible to remove. When contemplating recording at home you must select a room to use that is free as possible from reverberations (echoes). For example, do not attempt to record in the bathroom! The short distances between the walls plus the hard surfaces such as tiles, mirrors, counter tops, lavatory, sink and tub, combine to create a strong "ringing" type of reverberation that would mask over the recording of your voice. (Try this only if you want to experience some "worst-case" effects.) Rather, you should select a fairly large sized room if possible, but not the full empty basement please. The larger rooms generally will delay the reverberations so as to make them more acoustically acceptable. The room preferably should not be square in shape. (See Chapter 4 on studio design considerations.) The room should contain carpet, lots of stuffed furniture, and hopefully, many full length heavy draperies. These types of materials help absorb some of the sounds and reduce the reverberation loudness. Do not set up your recording location near the center of the room. Pre- ferably, you would try to set up near a corner, but not too deep into it, with heavy draperies hung on both of the walls behind you. The reason for this is that if you are using a cardioid microphone, as I hope you will be, it will face toward you and also be pointed toward the draped walls. Thus your voice sounds are directed into the sensitive axis of the microphone and then continue to travel the full length of the room before striking the opposite walls, then reflecting and returning back toward you. The distance covered by the sounds to the far wall and back again will tend to decrease their volume due to our old friend, the inverse square law. When these reflected sounds arrive back at your microphone, they are approaching from the backside, which is the "deadest" or least sensitive direction of the cardioid microphone's polar pattern and they are greatly ignored by the microphone. These reflected sounds continue to travel toward and then past you and strike the draperies behind you. The soft thick material of the drapes will absorb considerable sound volume before reflecting and returning the sounds back into the front of your microphone. This certainly doesn't even come close to replacing a studio room, but it is about the most optimum arrangement you can choose in the typical residential setting. Please understand that this suggested set-up technique will exhibit great variations in it's level of success due to the vast myriad of environmental differences from one room to another. In general, this will be the prefered starting approach, but due to the very complex character of acoustic behavior, some modifications, adjustments, and refinements may well have to be employed to achieve the most desirable performance. If that sounds to you like a "disclaimer statement"; it is because it is one! Acoustics is an extremely complex science which sometimes seems to border on being a form of "black magic". Actually it really isn't that much magic, but if everything in the environment isn't considered and accounted for then the resulting effects can be quite surprising and often confusing to interpret. Just remember the basic principles and apply them and you should be "O.K.". Often, in recording studios, sound absorbing panels are set up between performers to absorb, block, and generally help control sound travel. These are usually fairly simple panels made of sound absorbent materials such as fiberglass, and appear to be much like the semi-portable wall partitions often seen between desk areas in office spaces. They can produce fairly dramatic effects if properly employed. Another common application of this idea is frequently seen as small enclosures around pay type telephones which are mounted on a wall. Think about these ideas and use them to solve your difficult problems and/or improve your present quality. Incidently, devices such as these are quite easy to construct and not really very costly, so don't think you have to purchase everything. About the cardioid microphone you are using in this home recording environment. I would hope it is a good headband type like the Beyer units previously mentioned. But if not, then be careful of where you mount the stand for it. Shocks and vibrations, even very, very small ones can be readily picked up by the microphone. Therefore, be cautious about setting the microphone stand on the same tabletop you are sitting at to read your book. Also, never, never, ever set the tape recorder on the same tabletop that the microphone is sitting on. The recorder's motor vibration and other operational noises, will be picked up by the microphone and spoil what may otherwise have been a good quality recording. I should probably mention that the recorders motor noises that can accidently get recorded are often hard to detect by the operator of that recorder. This is partially because they are used to hearing the motor noise of their machine and so they tend to ignore it. Also, it may be hard for them to tell the difference between the normal recorder noise which is coming from the machine and the same sounds playing back from their recordings. And, finally, many home grade tape recorders do not have good enough low frequency sound reproduction to enable the operator to hear these sounds when played back on their machines internal speakers. Meaningful quality evaluations of the tape recordings must be done on a good quality machine and preferably through the use of very good "Hi-Fi" headphones by someone who knows what to listen for. Please do not be too quick and willing to accept marginal quality "home-made" tape recordings. As has been explained, a little care and application of knowledge can go a long way toward obtaining very good recordings. The result of not correcting the usual errors is a recording which exhibits excessive hum and noise, extraneous background sounds, annoying room ambient reverberations, low effective volume of the subjects voice, and poor intelligibility. When such tapes are broadcast over your Radio Talking Book SCA channel, they will seem to have a hollow, dull, even boring sound characteristic. This can quickly cause listener fatigue and ultimate disinterest in your programs by your listeners. So, it is very critical that you assure that you obtain quality performance from all of your microphone applications and especially when used in home recordings so that most listeners won't even be aware that they were made outside of your studios, in someones home.