Steve, Thanks for your suggestion.If that's the case, then I would expect the problem to also occur if you record onto a flash card in the H2. This could be useful for testing whether it's the Mac, the Zoom, or both that are a bit out. The digital recording on the flash card can be copied to any number of computers / MP3 players / audio CD / ...
I think it would be worth testing such a recording by playing on multiple devices to see how much variation in speed there is on different devices.
Let me explain more what I said in the original posting. I have recorded many times in the past (live or through line input) onto SD card inserted in the H2N, transferred the file to mac and then used Audacity for editing. That works fine without any pitch shift I am talking about. That makes sense because there is no sound card clock frequency clash when a digital file (.wav or mp3) is transferred from SD card to mac.
However this time I was trying to use H2N as a USB mic and record directly onto mac using Audacity program. This way I avoid the extra step of file transfers from SD card to mac. This is when I noticed the pitch shift in the recording. Here I see a frequency clash between H2n sound card vs mac sound card.
The same issue occurs when I use H2N as the USB interface and instead of using the built in mic of H2N, I give line input to H2N.
Again, I am looking to see if this has been observed before and how it was handled.