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Audacity woes

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I just recently had a problem with recording using Audacity and figured it out so I thought I would pass this along. Usually when recording I set the record mode to mono and I look at the waveform to make sure it stays less than 90% or so of the window in amplitude on the loudest notes. That way you maximize your signal to noise ratio (SNR) without harsh clipping.

Well the problem was that suddenly for no apparent reason the waveform wouldn't go over half the window in amplitude and was clipping. Since I was going through a mixer that had 3 level controls I tried adjusting the record level at each of the 3 controls and the computer record level. I went through each control trying to find if it was clipping at any stage of amplification. But no matter what I did I still couldn't get over half amplitude in Audacity.

Well I finally figured it out and here's what happened....

Sometimes I record in stereo to get a 2 channel recording. On my mixer I will pan the guitar to the left channel and the mic to the right. Then after recording I will split the stereo recording into 2 mono channels and then adjust the levels to get the final mix. It turns out that if you record in stereo then each channel left and right are depicted in Audacity as normal. Full amplitude is shown full scale.

The problem arose because I selected mono record but my guitar was stilled panned to the left. In mono mode Audacity mixes the right and left signals. So if one signal or the other exceeds half the amplitude of the record window it's clipped.

The moral of the story is if you want to record a mono track in Audacity make sure your input signal is present on both the left and right input channels at the line in jack. This doesn't seem to be just a visual thing with the window. You seem to cut your SNR in half by recording mono with only one channel coming in. If you have a signal on only one channel then you should record in stereo, split the tracks into 2 mono tracks, and then delete the empty one.

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Just a little update. I found the following in the Audacity help...

"Mono recording is not the same on all computers or sound cards. Sometimes recording mono only records the left channel, and sometimes it mixes the left and right channels."

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