I have been working with a new (to me) recording system called PMAR-XL. This system is available commercially as a passive acoustic package for the Seaglider. It was originally developed by the University of Washington's Applied Physics Laboratory (they originally developed the Seaglider before handing it over for commercial sale to a series of companies, which is now Huntington Ingalls Industries).
There is almost no information about this acoustic system available on the internet. It is listed as an invention on some UW faculty profiles (example here). And there is this report for the precursor to this system (I'm pretty sure...). It's a relatively new add-on by the manufacturer (and they are not acousticians) so their materials are pretty basic and just about operation.
The sampling rate of the system is set using a configuration file, and the maximum value is 180 000 Hz. The data is then lowpass filtered to prevent aliasing, and the max setting for this filter is 60 000 Hz. For each glider dive, a .eng file reports on the status of the acoustic system. In this output file, the sample rate is reported, and it is NOT 180 kHz. It can actually vary slightly from glider dive to glider dive, but is typically 180260.0312, but is sometimes 180259.1719 or 180260.9062. This is leading to some issues when I'm trying to use my normal analysis approaches, because they are expecting identical sample rates for all files.
So, my question is, how is a non-integer sample rate, that varies from file to file, possible? Could anyone explain this to me in as basic a way as possible?
My understanding of sample rate (with the caveat that I am a biologist becoming a bioacoustician rather than an engineer to bioacoustician knowledge base, so its basic) is that a signal comes in on a hydrophone or microphone, then this is digitized at the sample rate, meaning samples are taken at some specified interval...how would that change?