Re: Native Device Formats
Re: Native Device Formats
- Subject: Re: Native Device Formats
- From: "Mikael Hakman" <email@hidden>
- Date: Mon, 9 Jun 2008 13:11:46 +0200
- Organization: Datakonsulten AB
If you start sampling e.g. 23 kHz sine wave with 48 kHz SR at an unfortunate
time, you will have a large number of very small positive and negative
values slowly increasing. Only after many cycles the sample time will
coincide with actual peak or low. If this signal ceases before the sample
values reach any significant "height", and you then scale up the digital
values (because the signal is so low), then no headroom in the world will
help you. Therefore you should attenuate/amplify your signal before ADC in
such a way that the actual (not the sampled) peaks and lows are below FS
(and some headroom). Then, whether your ADC gets samples exactly at these
peaks and lows, or not, will be immaterial. Providing this sampled signal to
a DAC will then reproduce the original wave.
On Monday, June 09, 2008 10:56 AM, Dave Malham wrote:
Then, of course, there's the whole hairy question of intersample "digital
overs" where a signal re-constructed from a stream of digital words can
have positive peaks higher (or negative peaks lower) than the steady
state levels the digital words can represent (or the DAC they are sent to
can reproduce). If this seems odd, think of a max level sine wave at an
odd sub-multiple of the sample rate. Under these circumstances it is
possible for the sample points to fall either side of the peaks of the
sine wave, rather than on them, so the peak of the sine wave will be
implicitly, rather than explicitly, represented and can, in fact, actually
be over 0dBFs. This doesn't matter if all you are doing is storing the
signal**, but as soon as you do any processing in the time/frequency
domain it can pop up and bite you.
Dave
**It shouldn't really cause you any problems going to analog, so long as
the designer has done the proper, professional thing and allowed some
headroom in the analog part of the circuit - but that doesn't always
happen. :-(
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Coreaudio-api mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden