Inside Audio: David Moulton

The Brave Old New World

In all our gear-slut madness – that sick, demented, trembling need for the latest, coolest, bestest stuff on the market – which we all suffer from, especially around Christmas, we tend to ignore the old, the traditional, the known stuff.

Technology that has been around for a while tends to lose its luster, its coolness. It tends to migrate right off our little mental radar screens. We stop noticing it, paying attention to it, or thinking about its role in the scheme of things. We stop considering how we and it work together. Also, we often tend not to notice the incremental changes that have been happening to that old, stale, boring and all-too-familiar low-tech stuff.

TRANSDUCERS: THE FOUNDATION

Transducers, the devices that convert energy from one physical medium to another, are examples of such older (and lower?) technology. Microphones and loudspeakers have been around since 1930, and their primary design qualities have not changed a whole lot since then. They are old, valued and comfortable friends. We tend not to think about them very much, except possibly in slightly mystical terms.

This is, of course, a mistake. Both microphones and loudspeakers exercise a huge influence on the audio productions we generate – collectively they are the primary determinants of audio quality, and each of them dramatically changes the perceived quality of sound, in ways that are more significant and larger than any other audio devices.

Let’s consider microphones.

SO WHAT ABOUT MICROPHONES?

Microphones have a number of interesting characteristics. To begin with, they really sound different from each other, so that it is comparatively easy to ascribe specific sound qualities to them. Happily, it is also easy to measure differences between them as well, so we can look for relationships between those measured behaviors and our perception of how they "sound."

This leads us to the viewpoint of many recording engineers – that microphones are really like "paintbrushes," that they are our tools for representing any given sonic reality. We choose the right paintbrush to obtain the most compelling illusion in any given case.

We’ve all been doing this for a long time, and we’ve fallen into habits. I’ve noticed, for instance, that I’ve developed a long-standing set of "microphone moves" that I usually don’t deviate from very much. For drum micing, as an example, I usually go with: EV RE-20 on the kick, AKG 414 on the snare, any small pencil condenser on the high-hat, Sennheiser 421s on all the toms and a pair of large Crown PZMs taped back-to-back for the stereo overheads.

From this setup, I’ve got a nice reliable sound that clients seem to like, and I hardly ever take the time to mess with it, unless there is some immediate and special issue. It’s a combination of comfort, laziness, time constraints and economics.

PRETTY GOOD

What’s interesting about this is that these microphones are all pretty venerable now (even the PZMs are 20 years old!). Further, they are all considered to be at least "pretty good" microphones. The best of the lot would probably be the AKG 414, which, as you all know, is the solid-state multipattern condenser microphone descended from the legendary C-12.

If we were to move up to "very good" microphones, we would probably talk about using Neumanns (U87s and KM84s), plus possibly some Schoeps mics, maybe some B&K mics descended from their measurement microphones, and some other "high-quality" (er, expensive) mics – probably mostly phantom-powered condenser mics. Oh yeah, there’d be some tube mics as well, and maybe some stereo mics like the Neumann SM69. And we’d save, for "special" applications, our vintage tube Neumann U47, and maybe our old RCA BX44 ribbon mic for trombone overdubs.

This is all pretty obvious. You all know what I’m talking about here. Like, mics are mics! Old friends. And I mean old! So, let’s consider some of the facts about them.

THE 411 ON MICROPHONES

The older ones don’t have anything close to flat frequency response, and didn’t when they were new, either. Further, microphone frequency response changes dramatically as a function of angle, which is a large part of the distinctive sound quality of each microphone. Finally, the older ones are fairly noisy.

Bandwidth is limited by diaphragm size (the larger the diaphragm, the more limited the bandwidth), while noise is also limited by diaphragm size (the smaller the diaphragm the noisier the mic).

Another quirk of microphones has to do with what is called diffuse field response. With a large diaphragm condenser, if we want its average frequency response from all directions to be flat, we have to allow the response to have a distinct high-end peak on axis, just due to the physics of the matter.

Most older and middle-aged condensers have such peaks (8-15 dB at 10 kHz). This yields a really very striking breathy edgy effect with close-miced vocals, which early mics were probably not really designed to record. In the ’50s, such a response dovetailed perfectly with the deficient high-frequency response of speakers of the day, and voila, hi-fi was born. And along with hi-fi, we got dramatically inaccurate but profoundly beloved microphone sounds (the U47 on female pop and jazz vocal tracks) that carry over to this very day!

MIC QUIRKS

Also, you should know, microphones don’t detect sound the way our ears do – they lose a lot of auditory information. A couple of lossy quirks of microphones, vis-à-vis our auditory system, need to be noted. They dramatically affect the way we use mics.

Quirk number one is that microphones cannot distinguish the angle of arrival of various sound artifacts (as our ears do), so that all artifacts are merged into a single wavetrace that does not contain directional information. At the same time, the spectrum of that wavetrace is affected by the inability of the microphone to detect frequency equally in all directions.

Quirk number two is that microphones cannot integrate sound artifacts over time and sort them by phase (as our ears do), so that all early reflections (spatial cues for us humans) end up being interference effects for the microphone.

The net result of these quirks is that a great deal of sonic information that we humans use to make sense of the sonic world around us is lost at the microphone. The two-dimensional map of energy over time that comes down the mic cable is not a reasonable representation of the aural information that we humans use.

With all this said, we now are ready to consider how microphones, with all their beloved quirks, have evolved over the past 50 years, and what it means for us. To be continued … .

Thanks for listening

Dave Moulton is trying to re-wire his patchbay. Wish him luck! You can complain to him about anything at his improbable Web site, moultonlabs.com.