How does Audacity read multi-channel WAV files?


I have just started using Audacity and I am trying to use Audacity 2.0.2 on a Windows Vista 32-bit to separate a multi-channel PCM WAV file into single channel WAV files.

I am doing research to measure vibration levels using accelerometers. I am recording vibration levels with a 3 dimensional accelerometer and a 1 dimensional accelerometer. These recordings are saved to a USB drive in the form of a multi-channel WAV file. I import the multi-channel WAV file into Audacity and there are four channels, as I expect. However, Channels 3 and 4 are supposed to be measuring the same vibration levels and should be similar, but Channel 4 is about one third the amplitude of Channel 3 in Audacity. This occurs for all of my recordings even though the accelerometer device indicates both channels are measuring the same amplitude.

I am trying to figure out if the error is from the accelerometer device or the way Audacity is reading the multi-channel WAV file. How does Audacity read the multi-channel WAV file? Is it possible Audacity is incorrectly reading the WAV file and altering the amplitude of Channel 4? I’d appreciate any help or advice! Thank you in advance!

Audacity is not smart when reading multi-channel WAV files, and that should be good for you. It simply imports channel 1 as the first track, channel 2 as the second, and so on for the rest of the channels.

To help you test, here is a 1 second duration 4 channel WAV file that has the following channels, all with peak amplitudes of -6 dB:

  1. Sine wave 440 Hz
  2. Square wave 440 Hz
  3. Sawtooth wave 440 Hz
  4. White noise

Hi Steve!

Thank you very much for your quick reply. The attached picture is what Audacity gave me when I inputted the WAV file you posted. It seems to be the same as you have described each channel. If this shows that Audacity is working as it should be, in your opinion do you think my error lies somewhere in the WAV file before I even input it into Audacity?
4-channel Sample.jpg

The waveforms look a little strange because you’re using the “Waveform dB” track view, but other than that, yes it looks exactly right. I think the error must already be in your WAV file before it reaches Audacity.

Thank you so much for your help Steve! This has helped me to better understand Audacity and where my error might be.