David Bowles: So many mics, so little time

There are so many microphone types to choose from these days, it can be difficult to keep up. Audio engineer David Bowles breaks down some of the latest options, and asks whether there’s a need for quite so much variety…

First, the good news. In the past two decades, there have been many new microphones entering the marketplace which re-think traditional designs by taking advantage of interim research, modern materials and manufacturing processes. At the same time, analogue-to-digital conversion has improved immensely and exponentially more powerful DSP has made all types of digital recording better and more reliable. There has also been a demand for reproductions of vintage studio microphones, those which depart from those designs, and the inevitable cheap knockoffs.

However, digital microphones have not made the same quick progression for several reasons (which I’ll go into at the end of this article).

There are three types of newer microphone designs to be commended:

• Ribbon microphones using a combination of neodymium magnets,composite materials for the ribbon itself, modern transformers, internal shock absorption, perhaps incorporating active powering as well.

• Braunmühl-Weber microphones where each element provides separate outputs, which are recorded as separate tracks and can then be manipulated in post-processing.

• Short shotgun microphones, which also contain two elements, but add internal DSP to reject rear information (also recording both signals as two separate tracks for later post-processing).

Back to the old

There have also been several reproductions of large-diaphragm capacitor and ribbon mics of the 1940s and ’50s. These can be divided into two groups:

• Boutique companies striving for exact copies – these tend to be expensive and made to order. As those vintage microphone designs went through several revisions throughout their lifespan, modern companies have a certain degree of leeway in designing these reproductions. Interestingly, they are manufactured closest to how the originals were – hand-assembled in limited quantities, with minimal parts sourced elsewhere.

• Less expensive, but ‘trendy’-looking versions that strive to emulate ‘the sound’ of the originals. These might compromise via ‘streamlined’ circuitry, or offer fewer features of the original. They tend to have more parts sourced elsewhere, and might be assembled in other countries.

I also question the need for those microphones with high-frequency rise when using today’s digital recording chain. In the 1950s, there were many stages involved between the microphone and the finished LP. Mic cables and line amplifiers were of lower quality. Early analogue tape had considerably different sensitivity and response than what was available by the early 1980s. Finally, the mastering process involved several generations between session tape and stamper. These resulted in an inevitable loss of high-frequency response. Could microphones of the early 1950s have been designed to ‘make up’ for these losses, by emphasising high frequencies in response and directivity?

Since original valve models are no longer manufactured (and ‘B-stock’ inventory is low to non-existent), have any companies come up with a viable reproduction of the famed AC701 valve – and could this reproduction sound similar to the AC701 valve when new? It is my understanding that the frequency response curves of vintage microphones vary widely, particularly with regard to high frequency emphasis. I would contend that for better or worse, microphone manufacturers strove for consistency, and this was what led to the abandonment of earlier schema. With today’s low-capacitance cables, pristine mic pres and high-quality A/D converters, should modern reproductions aim for a flatter frequency response instead? Can one obtain ‘tube warmth’ without the brightness or hiss?

The new

There have been several mid- to high-price mics that depart from the ‘vintage wannabe’ paradigm with new design concepts. Some of these models have the imprimatur of a famed designer or engineer. To keep price down, some parts and/or manufacturing are sourced in other countries and often result in less-than-ideal sound. This begs the question as to whether higher quality control would result in these mics being used more widely.

There have also been even more mid- to low-price microphones from manufacturers known in the past for their line of high-quality models. Is the need for these models simply to increase their market share? If so, do the inevitable compromises in design and manufacturing result in a lowering of our expectations from those companies in general? Perhaps some of these manufacturers hope users of the lower-quality models will be directed into eventually buying higher-priced microphones in the future.

Bitstream of consciousness

The one area of microphone design I have mixed feelings about are AES42 digital microphones. These represent a paradigm shift with their streamlined signal flow, which includes phantom powering, preamplification, EQ, compression and even polar pattern choice with dual-element models. Few manufacturers have come out with AES42 microphones since 2002. Two manufacturers have adapted their interchangeable capsule models by providing a digital “module” to replace the analogue body (one of those manufacturers does have two ‘all-digital’ models, however).

Traditionally, we choose our sound palette via different mic pres and A/D conversion; these options do not exist under AES42 at present. All current AES42 microphones require a hardware unit to translate AES42 output into traditional AES digital signal. None of these ‘converter boxes’ take full advantage of the AES42 standard in offering 8x conversion or DXD, which is part of the AES42 specification. Similarly, none of the converter boxes available can interface directly with an AES67-compliant AoIP network (Dante, Ravenna, etc.).

What if we wished to use our favoured microphones and mic pres in an AES42 environment? No manufacturer has come up with an XLR plug to enable this. Such a plug would have to transform between DPP (12V digital phantom power) and 48V phantom power and would need to provide other types of microphone power, such as dual-element and active powering (60V, 130V, 200V, etc.). Further options would be to provide different impedances, and possibly a seven-pin model for vintage studio mics. This would open up a world of possibilities for many of us, bridging the old and the new.

David Bowles is a freelance audio engineer specialising in recordings of acoustic music in surround-sound and 3D audio. He guest lectures at New York University’s Steinhardt School Tonmeister seminar, resides near San Francisco, and likes good wine and bad puns.