The View From 2009: This article was the second in a series reviewing the state of audio gear for my TV Technology readers.

How Microphones Have Changed

Alert readers may recall I spent last month discussing something about the nature of microphones. I mentioned that they’ve been around for a long time, that we take them for granted, that they aren’t particularly accurate (particularly in their more venerated forms), and that they lose a lot of acoustical information that we humans use. I promised this month to talk about how microphones are in the process of some remarkable changes that we all need to concern ourselves with.

Postwar Microphones

After the end of the Second World War, the best microphones were those used for live broadcasting. These were tube-amplified condenser microphone designs intended for generic recording of medium-to-large ensembles in reverberant spaces (recorded in mono – often just a single microphone). Except for announcers, close-miking was the exception rather than the rule. The microphones of choice (such as the Neumann U47 and AKG C-12) were distinguished by a combination of factors – a sweet and warm musicality to their timbre and a wonderful ability (as seen in retrospect) to resolve low-level details, essential for the making of live orchestral recordings.

Multi-track Microphones

By about 1975, these classic designs evolved into solid-state designs such as the Neumann U87 and the AKG 414, which are still with us today. At the same time, the explosion of recorded popular music, rock and roll, and multitrack technology led to a variety of new design topologies. Some of these came from sound reinforcement, others from communications, and some simply arose as a function of new materials and technologies (the electret condenser, for instance). The primary developmental constraint for these new microphones was the need to cope with extremely high sound pressure levels (up to 150-160 dB SPL!) with consistency and reliability, arising from the almost universal abusages of close-miked high-intensity rock-and-roll performance.

The Great Digital Divide

Beginning a few years after the advent of digital recording and the general adoption of the CD, microphones once again began to evolve. Analog recordings had a noise floor (at best) of approximately –70 dBV, and so the self-noise of microphones had not been a big issue. Similarly, the move away from minimalist recording of acoustic ensembles had reduced our awareness of and desire for low-level resolution of complex multi-source sounds (essentially, we stopped recording such sounds for a while, preferring to close-mike everything up to, and sometimes even including, digeridoos!).

Beginning in the 1990s, the reduced noise floors of digital recording media (all the way down to about –90 dBV for 20-bit recordings) led to an increased sensitivity to noise limitations of mics and mic preamps, and started to raise the bar, once again, for microphone performance. At the same time, the growing use of measurement microphones for music recording (the B&K 4000 series microphones are directly descended from such mics) also illuminated the increasing possibilities afforded by an enlarged and scrupulously maintained audio window.

So, during the 90s, we have seen a steady improvement in microphone self-noise, so that a microphone that would have been reasonably highly regarded 20 years ago with a self-noise equivalent to ca. 25 dBA SPL is now mediocre in that regard. Microphones with self-noise around 15 dBA SPL are OK, while mics with self-noise below 10 dBA SPL represent the current state of the art.

At the same time, manufacturers have begun to notice that “flat” isn’t necessarily “great,” and have begun, once again, to develop “microphones as paint-brushes.” This has resulted in a plethora of modern “tube” and ribbon microphones, whose alleged virtues of “warmth” and “musicality” replace their sales arguments for “accuracy” and “flat frequency response.”

One fascinating tangent to all of this is the arrival of retro microphones from the Iron Curtain nations emerging from their Cold War isolation. The Microtech Gefell is a such a microphone, as are the Octava microphones from Russia. These mics are designed and manufactured using techniques and materials holding over from the 1950s and 60s, when the Cold War closed off the Western World (and multitrack pop recording markets) to Russia and Iron Curtain countries. Buying an Octava is a little like buying a 1957 Chevy made in 1999 after being in continuous production, but not much development, for the last forty years! A fascinating and very illuminating exercise.

So Where Are We Today?

Where does this leave us?

• Noise – we’ve seen a real drop in the noise floors of microphones and mic preamps, in an effort to keep up (er, down) with the noise floors now available from hi-rez digital formats. The result? Source recordings that are, at their technical best, far more transparent and free from obvious electronic artifacts than ever before, as well as more revealing of acoustical limitations and deficiencies.

• Low level resolution – once again, an effort appears to be underway from manufacturers of condenser microphones to make their mics yield compelling detail at very low signal levels. The diversification of recording styles and genres has also fueled this.

• Dynamic Range – we haven’t given up our high sound pressure levels, so we’ve had to develop microphones with some really stellar dynamic ranges – finally, at 130 dB, almost equal to what the human ear is capable of perceiving.

• Timbral color – manufacturers have an increasing awareness that the way a microphone “sounds” is probably more important than ANY of its other virtues, and they seem to be paying increased attention to the nature of this often ineffable subjective quality.

• Directionality – the best directional microphones are getting a lot better at achieving decent frequency response off axis. This results in greatly enhanced stereo and surround recordings and imaging, as well as performance stability.

What Does It Mean?

If we were all to start over today, start buying all of our microphones from scratch, we would find that there are a BUNCH of exciting new microphones out there, from both new and old (and new old) manufacturers. These microphones can yield remarkable sonic quality and an enhanced audio window. Also, happily, some of them begin to give us the kind of musical warmth and sweetness we got so hooked on in the fifties and sixties. It’s really pretty exciting and gratifying.

Thanks for listening.

Dave Moulton would like to thank Tom Bates for his insights and suggestions for this article! You can complain to Dave (not Tom) about anything at his website, moultonlabs.com.

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