Soundcard Verification

I was recording analog audio into my computer (FreeBSD) using my external Edirol UA-25 USB soundcard. The audio sounded a little but funny, but I wasn't sure. I thought that perhaps audio was being dropped, as if the audio were a tape and a few millimeters were being cut out here and there. To test this hypothesis, I connected a 35-Hz triangle wave generator to the sound card input, and recorded one minute of audio. Then I wrote a little program to calculate the difference between each sample and the sample before it. If the recorded waveform is a true triangle wave, there should be only two values for the slope, rising and falling. If there are skips, it will (most likely) lead to some sample having a very different value than its predecessor. I sorted the output of the differencing program so that the biggest differences were at the top of the output. There were no big differences. My hypothesis about data being dropped was wrong. Anyway, I'm glad I now have a procedure for testing for dropped data.