rs
Paul Dickinson wrote:
> Could it be that what you're hearing is the nyquist freq. foldover
> from sounds in excess of 22kHz? I know that digital recorders employ
> brickwall filters at around 20k, but maybe they're less than perfect
> and the amplitude is in excess of the filter's capabilities? Hence
> you would hear artifacts resulting from the difference of the
> original frequency minus 1/2 the sampling freq. e.g., 24kHz-22050Hz
> =3D 3500Hz. Add that to your original signal and you'd end up with some
> interesting inter-modulation distortion.
What I'm finding is a perfectly natural sound, it's out there and the
mic records it. It's not any kind of digital error. The real world just
does not play by our sound recording rules.
It is a clear beat frequency between the calls of two or more frogs in
my case. It's also possible to get this sort of thing if you have a
strong multipath signal. ie. things out in the environment are
reflecting signal at you out of phase. I've also heard this from insects
as well. In both cases I can hear it by ear at the original site.
I've not seen any foldover problems in my gear, even when you overdrive
digital, it's easily explained by the fact that sampling is discrete
intervals. When you clip, it's not a single new frequency that's
produced, it's a whole series in even steps.
We did see some foldover when we were discussing slowing sounds by
forcing them to play at different sample rates. At least with one model
of iMac. I don't think we sorted out exactly how it was doing it. Could
have been a programming error rather than hardware.
Walt
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