>>Could somebody please advise me which bitrate I should use for
>>encoding 32 kHz audio?
>As with any sample-rate, it depends on the content. If it is Orchestral
>music which has a lot of content to mask compression artifacts, you could
>get away with 96kbit/s, but if it is more minimalist (like vocals with
>guitar and bass) even 128kbit/s will sound a little 'squishy'.
I would give the completely opposite advice. MPEG compression builds on
psychoacoustic theory just like noise suppression, but it definately doesn't
have the same characteristics. If there is something that MPEG-audio has
trouble compressing into a given bitrate, it's orchestral stuff and
everything else that has a broad loud spectral contents like choirs - most
of the spectra is so important that you can't really add noise (compress)
anywhere (exaggerating a bit here). You could put in unaudible noise in the
few silent energies like you suggest, but it really isn't enough.
On the other hand, a bass and a vocal is compressed very very nicely using
MPEG compression, because the spectra is so scarce and free of transients
that the available bits can be used to quantize the existing energies less
The mpeg compression artefacts are easily distinguishable in all
compressions of orchestral music I've heard, but they are much harder to
hear in traditional rock.
Quote:>The lower samplerate only reduces the upper frequency limit from ~20kHz to
>~16kHz, this high frequency information is usually removed during
>compression since normally, it is relatively inaudable (perceptual
>compression) - now it simply isn't there. So you still need about the same
It is true that if there is no spectral information in the upper frequency
regions, then you would not really get any gain from using say 48khz instead
of 32khz. On the other hand, if there IS spectral audible content, then it
would sound bad if you cut and use 32khz samplerate. If you have no other
option though that is the way it has to be.
So why don't you just compress whatever you have in both 96 and 128 kbit and
listen to see what sounds best? After all, there is no way to objectively
specify the performance of psychoacoustical compression schemes. All
"specifications" arise from subjective listening-tests.