Recording - June 2012 - 37

or comedians tend to explosively shout into a handheld mic. Use them sparingly, though, as foam windscreens can also greatly affect high-frequency response. Don’t be sensitive Microphones vary in sensitivity. Technically, sensitivity is the output voltage of a mic when faced with a reference sound pressure level (SPL). Put simply, sensitivity rates microphone loudness. By comparing various mic sensitivities, you can tell which mics are louder or softer. Why does this matter? Louder mics require less gain at the microphone preamp, which usually translates to less noise in the signal. (All gain stages add noise.) Traditional ribbon mics, for example, typically have very low output levels. To counter this, many modern manufacturers offer active ribbon mics, which borrow from condenser designs and include a amplifier inside the microphone body. The amplification circuits employed in active ribbons vary, from tube-based to solid state, and thus many choices exist for modern recordists. For those of us using lower-output passive designs, several ribbon-focused preamp products exist specifically tailored to provide quiet, plentiful gain. AEA’s RPQ preamps are a good example, and Cloud

über-loud sources, such as inside a bass drum or directly in front of a speaker cabinet, must withstand high pressure. All mics will overload when facing extreme volume, and the max SPL rating informs the user at what pressure point a certain percentage of distortion will be heard in the signal. Dynamic microphones typically have few problems with high SPLs, and hence have found popularity in drum and amplifier miking. Ribbon mics, on the other hand, have traditionally been poor handlers of extreme pressures, and thus most engineers avoid placing classic ribbons close to loudspeakers, horn bells, and drumheads. Interestingly, modern ribbons are engineered for higher SPLs, and are now popular for miking amplifiers and brass instruments. Condenser mics have a unique relationship with extreme SPLs. While condenser diaphragms themselves typically withstand high-level sound without issue, the higher voltages generated by the capsule in these situations often overloads (clips) the built-in amplifier, producing a nasty distortion. To avoid this problem, many condensers include a pad to reduce the level between the diaphragm and the amplifier and thus avoid clipping. Microphone pads come in a variety of flavors, with many switchable for varying degrees of attenuation. Some are

Check out the video on Recording’s website, where we demonstrate the proximity effect: www.recordingmag.com/videos/videoDetail/12.html
Microphones makes the CloudLifter, a phantom-powered inline amp that converts a passive ribbon into an active one. On the other side of the spectrum, condenser mics are usually the most sensitive, often delivering levels much louder than their dynamic and ribbon cousins. This increased output can be attributed to the presence of amplifiers built into all condenser mic bodies. Internal amplifiers, a necessity as condenser capsule outputs are of low level and high impedance, help make condensers the quietest of all mics. Related to the discussion of sensitivity is that of microphone self-noise. All analog audio devices contribute some amount of noise due to the random movement of electrons in their circuitry. Self-noise is the amount of noise (usually high frequency hiss) inherent to a microphone itself. When self-noise is measured, an equivalent noise rating is the result. While microphone selfnoise is rarely an issue with loud sources such as drums, horns, and electric guitars, mics with low noise ratings are usually preferred when recording quiet sources such as classical guitar, harp, and when distance-miking softer musical ensembles. Also important to consider is the maximum SPL rating of a mic. Microphones placed on even screw-on accessories added between the mic capsule and body. An important note about microphone pads is that though they are required when miking loud sources, they should be avoided when not needed. Unnecessary padding reduces microphone output level and requires additional gain at the mic preamp. Both of these outcomes reduce signal-to-noise ratio and make the source noisier. (The photo on the facing page shows a typical 20 dB pad switch on a condenser mic.) Conclusion We’ve dedicated three months’ worth of this column to the topic of microphones, and we could go on forever— mics are a fascinating subject. But we’ll move on, leaving you to rely on the mic discussions and mic reviews that Recording publishes every month. We’ll move on to new ground in next issue’s Recording Fundamentals. Until then— Keep on listening! Eric Ferguson (ferguson@recordingmag .com) spent a dozen years as a freelance audio engineer in Los Angeles, and is now on the faculty of the New England School of Communications (NESCOM) in Bangor, ME.
RECORDING JUNE 2012

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Recording - June 2012

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