Adventures In Audio
USB microphones - has their time come?

David Mellor

David Mellor is CEO and Course Director of Audio Masterclass. David has designed courses in audio education and training since 1986 and is the publisher and principal writer of Adventures In Audio.

Friday February 5, 2010
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Some makers of quality mics now have USB models in their range - Audio Technica and Blue are two companies that make mics of unimpeachable excellence, and have chosen to give USB a try.

Just for clarity, let me explain the difference between using a conventional microphone preamplifier and connecting via USB.

Dynamic microphones, which include ribbon microphones, have a low-level output that needs careful handling to give the best signal-to-noise ratio and frequency response. Capacitor microphones have an internal amplifier, which traditionally has been of fixed gain providing just enough 'urge' to get the signal down the cable. The output of a capacitor microphone is therefore nearly as fragile as that of a dynamic.

Microphones therefore need special preamplifiers. Anything else will plug into a line input with no bother.

The preamplifier might be combined into an audio interface that will convert it to a digital signal, which can be fed into the computer through a USB or FireWire socket. Or if the preamplifier is separate, its output is connected to the line input of the audio interface.

Microphones that connect via USB have a preamplifier, analog-to-digital converter, and circuitry to produce a data stream compatible with USB, all carried internally.

To be honest, connecting via USB cuts out a lot of bother. Anyone recording, say, a podcast where the ultimate in audio quality isn't really required, will probably be happy with the results.

But for 'proper' recording, can a USB microphone cut it?

"No, not yet" is the answer.

The problem is in setting the gain. When working with microphones it is essential to set the gain of the preamplifier correctly. Too little gain and there will be too much noise in your recording. Too much gain and there will be clipping, leading to distortion.

Yes, you can set the level of the signal from a USB microphone using the sound input control software in your computer. But the problem is that whatever damage that an incorrect gain setting will cause has already been done. You're just preventing it getting worse.

So for that reason - and that one reason is enough - USB microphones are not yet suitable for pro audio.

But...

What if the gain of the internal preamp of a USB microphone could be controlled (other than by a basic pad switch)? There is no reason why this couldn't be done from the computer with data going back through the USB connection.

For best results the microphone would have to have a motorized potentiometer or relays to set the gain.

Potentially this could be even better than using a conventional preamp because the manufacturer could optimize the preamp to the microphone.

Perhaps in the future we will all be using USB (or whatever comes next) microphones, and preamps as we know them today will be dead?

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