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Q: "Why is the signal from my microphone low in level and noisy?"

Sometimes a perfectly adequate microphone connected to a perfectly adequate audio interface will sound pretty bad. But there's an easy explanation...

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Here's an issue that comes up two or three times a year with students who are new to Audio Masterclass. We listen to their first project - a simple recording of speech - and it is low in level, or noisy, or both, even though the student has a microphone and audio interface that are both capable of good results.

In all the cases that I can remember, then where there was no fault condition present in the equipment, the problem was caused by connecting the microphone to the interface by an XLR-jack cable, rather than an XLR-XLR cable connecting correctly to the microphone input.

I can see how confusion can arise, from two sources. Some lower-cost microphones are sold with an XLR-jack cable. Some interfaces have input connectors that combine XLR and jack sockets.

But according to the conventions of professional audio, microphones always connect via an XLR connector to a proper microphone input. This input is optimized for the signal level and the other expected parameters of a microphone.

The jack socket is a line input. Line-level signals are much higher in level than the signal from a microphone and do not require as much gain, or such careful handling, line-level signals being inherently more robust.

Fortunately the solution is simple. Invest in an XLR-XLR cable and connect the microphone to the mic input and all will be well. Now you just have to set the correct gain (which is another story in itself...)

P.S. Audio interfaces in the lower-cost range usually incorporate a microphone preamplifier these days, perhaps two. But if there is no XLR connector labeled 'microphone', then there is no proper microphone preamplifier present. A separate microphone preamplifier must be used.

By David Mellor Friday August 2, 2013
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