radio sample rates.

[Jim web]

In article <mpro.nl9kix00g3lj401n0 at wingsandbeaks.org.uk.invalid>, Jeremy
Nicoll - ml get_iplayer <jn.ml.gti.91 at wingsandbeaks.org.uk> wrote:
> Jim Lesurf <web at audiomisc.co.uk> wrote:

> >This is all for *sound radio*...

> Ah you traditionalist!  Don't you look forward to touch & sniff radio?


> >In case anyone is curious, I can tell the sample rate because the audio
> >DAC I use indicates it. In general, it switches to 'follow the source'.

> So the audio stream isn't just audio data then?

Afraid that's a muddled question to ask.

Audio is essentially always sampled at a specific rate. When LPCM is
converted into other forms like mp3, flac, aac, etc, then they will have an
associated rate. 

>  I kind-of assumed that you might be able to play a stream at any
> sampling rate you liked, though that would alter the time taken to play
> a clip...


Well, you could choose to playback at the 'wrong rate' in order to speed
up /sharpen or slow down / flatten the sounds. But in practice you're
more likely to encounter rate *conversions* if you want to hear things
at the right speed / pitch. That requires data manipulation.

So you can convert the rate. But all such conversions carry the risk of
degrading the result. So its best avoided unless there is a specific reason
to do it.

In particular 44.1k <-> 48k conversions are a real challenge to do well
because of the close ratio of the rate values and the high integers for the
lowest common ratio. Its much easier to make 48k into 96k well than convert
from 48k to 44.1k. 

Jim

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