Thanks David - that makes a whole lot of sense. I remmebr recording insect =
sin Peru once and wondering where this weird low frequency buzzing was comi=
ng from - I guess the anti alias filter want working (it was an old dat pla=
yer). i gess the 680 with 92 khz, or 192 khz should be ok then....
--- In "Avocet" <> wrote:
>
> > I could be wrong here - but from what I remember of my sound
> > engineering course the sample rates only allow you to sample
> > frequencies of HALF their stated value.
>
> Gus,
>
> That's the "Nyquist Theorem" which states that any frequencies above
> half the sampling rate would "reflect" downwards at a difference
> frequency. In other words sampling at 44.1, a sound of 35Hz will
> appear as a sound at 9.1KHz. You wouldn't know whether it was 9.1KHz
> or 35KHz. They therefore need a sharp LPF filter on the input at about
> 20 or 21KHz. These are built into digitisers.
>
> Theoretically you can sample a 20KHz input at 44.1Ks/s, but it will
> only have two samples per cycle, so it won't give a sensible 20KHz
> back. With music, anything up there is hash, but wildlife calls need a
> better reproduction than that.
>
> Repeating myself, check that anything sold as as audio device may
> sample at high rates to give a high quality but could well be limited
> to around 20 or 25 KHz. Check the spec. :-)
>
> I've picked up unidentified rodents most likely shrews or voles at
> around 15HKHz sampled at 44.1, but all I can really derive is an
> approximate frequency. Slowed down, the calls are very gravelly.
>
> David
>
> David Brinicombe
> North Devon, UK
> Cogito cogito ergo cogito sum - Ambrose Bierce
>
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