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Q: Should microphones have USB cables?

An Audio Masterclass Newsletter reader has a USB microphone. Would he be better off with one that has a normal cable and connector?


A question from an Audio Masterclass Newsletter reader...

"I bought a Behringer condenser microphone. The interesting thing is that it has this USB cable instead of the normal three pin microphone cable. What's your opinion on microphones that use USB cables rather than the normal one?"

Let me play god's advocate (I guess that's the opposite of devil's advocate) and set out the case for USB microphones as opposed to the conventional type that connects through an XLR cable.

The potential advantage of a USB microphone is that it can right a number of wrongs that have been around for far too long.

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Firstly there is something inherently wrong in a capacitor microphone having an internal preamplifier (which they all must as the signal from the capsule is too weak to travel through more than a meter or so of cable), then having another preamplifier at the end of the cable.

Why two preamplifiers? Why doesn't the microphone just have one preamplifier mounted internally, thus giving it a robust line level output? The answer is 'historical reasons', which modern technology can now do without.

Think about the conventional microphone preamplifier. No, you have thought about it too much already! People waste eons of time worrying about their microphone preamplifier and whether it is good enough. And if it is good enough they worry about whether it is the right one for their mic.

With USB microphones, the conventional microphone preamplifier is placed where it ought to be - inside the microphone! Not only is this a better place because it's physically closer to the diaphragm, it also gives the manufacturer the opportunity to optimize the preamplifier exactly for the microphone.

If you're not convinced that this is the right thing to do, then consider this... You spend a lot of time worrying about your preamplifier. Why don't you spend just as much time worrying about your microphones' internal preamps? They are just as important, and arguably more so.

So the USB microphone takes the microphone preamplifier and puts it where it belongs, inside the microphone. Are there any other advantages?

Well yes, the signal chain doesn't stop at the preamplifier. Next comes the analog-to-digital converter.

Assume a conventional microphone but with a line-level output. The signal, although robust, has to travel through meters, perhaps many meters, of cable before it meets the converter. Wouldn't it make more sense to put the converter inside the microphone too, so that the microphone has a digital output? Once again you wouldn't have to worry about converters because the microphone's manufacturer has done all that for you.

In a world populated with USB microphones, you would choose the best-sounding microphone for the particular job in hand. And since it has an internal preamp and converter, you can be sure that the digital output is a perfect representation of the electronic signal created right there in the microphone's capsule, which is surely what you would want it to be.

OK, I'll stop being god's advocate now. Surely there must be some problems with this...

Well one problem is the lack of choice since USB microphones are few in number. Well a little bit of industry could solve that.

Another problem is that the gain control, which was once on the microphone preamplifier, must now be on the microphone. That could easily be fixed with a common standard for remote gain control. Bear in mind however that to do this properly requires relay switching in the mic. I can guarantee this will be an issue if USB mics ever really take off.

Perhaps the most significant problem however is that USB is here today, but it will without doubt be gone tomorrow. Would you spend, say, $1000 on a high-class USB mic, and feel confident that you could still find a USB socket to plug it into in five years' time?

In conclusion therefore, I see no reason why microphones should not have internal preamplifiers boosting the signal to line level, and internal analog-to-digital converters too. (To be picky, line level might not be necessary in such a circumstance, but it is part a development from conventional mics to line level mics to digital output mics.)

Setting a standard for connection that will last as long as the XLR connector has lasted will definitely be the tricky part of all of this. Other than that however, the USB mics of today could be pointing a route to the future.

What do you think?

P.S. The mic pictured is an Audio Technica AT2020 USB.

By David Mellor Friday April 8, 2011