What they do and why. Chris Dale continues to ponder the sound, shape and purpose of modern microphones.

One thing you're unlikely to be short of as a prospective microphone purchaser is choice. In fact it's more likely that you'll become saturated with alternatives. It's possibly this daunting plethora of apparently similar models that has the majority of us on the transducer trail plumping for the good old established names such as Shure and AKG etc.

The term "flat" is often used with regard to audio equipment to denote high quality. It refers to the shape of the graph of a unit's frequency response curve where the microphone's electrical output is plotted against the frequency of the acoustic information being received by it.

If it puts out a significantly greater voltage for low frequency acoustic signals as compared to those of the same strength at higher frequencies, everything will sound muffled and boomy. Conversely, a mike that reacts more strongly to high frequencies will produce thin, tinny sounds. A flat response, ie a reasonably straight, horizontal line, will show that the microphone is capable of constant, faithful reproduction across a wide band of frequencies.

However, it is true to say that the modern music recording industry is seldom in the business of making facsimiles, it is generally more interested in creating its own specially tailored versions of a given sound. For example, few new artists are interested in the natural timbre of an untreated drum kit, and a "flat" representation of a vocal just isn't big enough to wtftsfy present tastes or consumer expectations.

Hence the microphone manfacturing industry can get away with churning out dozens of different models, claiming that each has a uniquely special sound. Undoubtedly, some mikes are better than others for certain jobs, but it certainly doesn't follow that a more expensive unit will always serve better than a cheapy.

This is where the great question of capacitor vs dynamic arises. The capacitor's superior frequency response stems from the fact that its diaphragm is usually many times lighter than the dynamic equivalent, and thus it is able to react fair more quickly and accurately to changing acoustical information. It is also more sensitive than the dynamic, meaning that for a given acoustic level it will produce a greater electrical output with relatively less unwanted noise.

Now that the (nearly) all digital recording studio is with us, the demands on the rest of the recording chain are substantially increased, and capacitor microphone technology is being stretched even further to meet the new demands. Even so, for certain applications, especially in home and live use, the capacitor's high flown qualifications are often unnecessary, even positively undesirable.

All engineers have their own preferences, but many will acknowledge the inexpensive Shure SM57 dynamic as an excellent snare drum mic, whilst decrying a more expensive capacitor as thin or, somehow, simply "not right". A mike that is highly sensitive and which picks up every little rattle or resonance may be regarded as "too fussy" for use on a kit, because it brings forward those undesirable components of the sound.

It was once the case that capacitor models were too delicate to withstand any physical knocks, and also too sensitive electrically to withstand the high sound pressure levels kicked out by drums, guitar amps, closely miked brass, etc. Many modern devices are physically extremely robust and can cope with practically any sound level. Also, companies are designing models with specific tasks in mind. One such example is the AKG C535, a pre-polarised capacitor (electret) designed primarily as a hand-held vocal mike equally at home on stage or in the studio. It combines compactness and physical ruggedness with the wide, sensitive response of a capacitor system, all at a reasonable price.

The more expensive dynamics and capacitor mikes often include a switchable system of attenuation and filtering, so that their response can be tailored to suit a given situation, so broadening their scope. In a less sophisticated home recording or live set-up, these features can be of great help in creating the right sound before it reaches the console or tape recorder.

One facility offered by multi-diaphragm capacitor mics unobtainable with dynamic technology, is the ability to switch polar response patterns either via switches on the mike, or remotely. Probably the most famous example of this is the Neumann U87, which is often hailed as the studio vocal mike. The design of such mikes makes them unavoidably bulky, and, in the case of the U87, very delicate and sensitive to humidity.

Before solid state circuitry, there was the valve, or the 'tube' as the Americans call it. The warm, open sound of valve guitar amps need no introduction, and the same quality is present in valve based microphones.

It's all to do with the unique transfer characteristic of valves, and though many have tried, the quality can't be reproduced with semi-conductors.

AKG have fairly recently brought out a mike which they are calling "The Tube", that combines a basic tube transducer with the benefits of modern technology and the performance advantages it brings. Predictably it sounds great, although, just as in the old days, if you drop it once, you'll most likely need a new tube.

When it comes down to it, there are probably many models that will do the job, whatever it is. Usually, the more important consideration is where you place the mike and what you do with the signal once it leaves, and that, to a large degree, is down to practice.