Hearing The Microphone

To hear a microphone, rather than the voice or instrument it is picking up, is often a great insult to the mic's performance. However, to listen to the mic and know its inherent qualities is an essential skill for anyone that must decide which mic will best suit a specific application. Evaluating the critical aspects of a mic's sound must be done first hand, requiring both critical listening skills and an understanding of the intended application. Developing a system to make this evaluation will be even more critical as we can see emerging mic technologies on the horizon. These new designs use innovative methods to capture the movement of air molecules and new solutions to getting the audio signal to the mixing console.

How do we decide that a particular mic is suited to a task? In recording sessions, it may be possible to put several mics up near the instrument or vocalist and compare the results in the control room. However, in live performances the conditions of a sound check or rehearsal are not always sufficiently similar to a performance to develop confidence in a new mic, let alone the luxury of listening to several mics side-by-side. In live sound, the mic that doesn't survive a plosive-consonant (popping Ps), or that first big drop to the stage, cannot redeem itself with even the most awesome sound quality.

For live sound techs, there are a few parallels with loudspeaker criteria that suits this form of evaluation. The presence of the instrument or voice is a combination of the on-axis response and off-axis response. Just like stage monitor loudspeakers, a flat on-axis response may not suit every application and, unlike the FOH loudspeakers, the characteristics of a specific mic need only meet the needs of one voice or instrument. Getting the right tonal qualities from the output of a mic always beat applying remedial EQ on the input strip. The off-axis response of the mic will influence pickup of leakage and ambience but also must provide adequate rejection of stage monitors and venue noise. A smooth sounding off-axis response will not only improve the sound of leakage from other instruments; it may also achieve greater gain-before-feedback.

Perhaps the ideal situation to evaluate a new mic is when there is access to both the controlled conditions of a quiet recording studio and the chaos of a live venue. In the studio, a fine instrument and voice can offer a detailed audition of the mics tones and textures, especially when in an A/B comparison with a familiar mic. Careful matching of levels (try reversing the polarity, setting for maximum null and resetting the polarity) is essential to making the best comparison of sound quality. Voices are particularly good for this form of testing, as we are so highly attuned to the subtle changes in tone and perspective that the mic can impart. It is important to have the sound source moved to various off-axis angles to hear the way the qualities change. These off-axis changes will influence a larger number of sound sources than the on-axis pickup, including sound reflected from the stage floor.

Once a sense of the sound qualities of the mic have been developed, then it is time to put the device in jeopardy. On stage, not only will all the tones of clinical evaluation will be in play; there will also be the potential for unexpected trauma and maybe even inappropriate use. Seeing how a mic stands up to being on the saxophone for the first set and then become a backup vocal mic in the last set (should've reconsidered that windsock…) is exactly the type of use you need to hear in order to have long term confidence in any new addition to your mic kit. You may not want to use the new unit on the headliner first. After all, this is what the warm-up band is for, right?

Our ability to evaluate new mics may really be put to the test over the next few years, with manufacturers replacing audio cables with digital links and even finding new ways to detect the sound radiating through the air. There are mics, such as the Beyer MCD 100 digital microphone, that digitally transmit the audio from a conventional mic capsule to the mixing console and even those that do it without wires, such as the Zaxcom digital wireless mic (which allows you to remotely adjust the mic preamp in the bodypack). There are even more radical ideas being developed to detect the sound wave using light, such as the prototype demonstrated by Sennheiser. While the former examples will simply change the way the resulting audio reaches your mixer, the latter example may even challenge much of what you know about mic performance.

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