Well…don’t think its the POD…
If you’re not using your regular soundcard for recording or playback, it’s either the POD or the POD drivers.
Background - With digital, the pitch & speed (tempo) are directly related to the sample rate 44.1kHz or 48kHz, etc. If there is no clock, there’s no sound… If you record at 48kHz and play-back at 44.1kHz, that’s about a 9% drop in speed & pitch (and if I recall correctly, that’s more than a half-step, but less than a whole-step). If you’re off by about 9%, that’s a possible clue.
If you understand the basics of [u]how digital audio works[/u], you’ll understand that the ONLY way pitch can be accidently changed is by accidently changing the sample rate. (And with analog, the only way to change pitch is with mismatched recording & playback speeds.)
It’s the driver’s responsibility to communicate the correct sample rate between the hardware and software and more than 99.9% of the time it’s foolproof! The sample rate is stored in the audio file (or as part as the Audacity project), so when you play a WAV or MP3 file, it plays at the correct speed and pitch.
Sometimes S/PDIF connections (optical or coax) can get fouled-up because the hardware and software are not directly communicating. But, I believe your POD uses USB and that should be foolproof.
Or, as I mentioned before, the internal hardware clock can be off. If the software & drivers tell the device to play-back at 44.1kHz, but the hardware clock is a little slow or a little fast, the software (and drivers) will never know and it will play at the wrong speed/pitch. However, the soundcard or interface will use the same clock for recording & playback. If it records a little “fast” and plays-back at the same speed, you’ll never see a problem until you play-back on different hardware.
FYI - It’s virtually impossible to accidently change the pitch without also changing the tempo. If you’ve every played a vinyl record at the wrong speed, you know that pitch & tempo change together. The same thing happens digitally with the wrong sample rate. It requires a complex computer/math algorithm to change pitch without changing speed.
…It’s theoretically possible for Audacity to write the wrong sample rate into a WAV file header. But it’s highly-unlikely, and these pitch problems only seem to happen to POD users. Plus, nobody has ever seen the wrong sample rate written to the header by Audacity.
…It’s also possible, but highly-unlikely that the clock in your POD drifts over time… Maybe it starts-out at 44.1kHz and over an hour or so drifts to 42 or 46kHz, etc.