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Re: Frequencies was Re: AW: AW: OT: new Macbook wíthOUT Firewire :(
Uh oh, I find it hard arguing with an authority like you ;)
Bob Amstadt wrote:
> I haven't done a research study on sample rates, but I have studied the
> subject in the classroom and in the real world. As you increase the
> sample rate, you build a better quality representation of the original
> signal. In terms of what you hear, this will translate to a lower noise
> floor. Personally, I don't know how much better, but if you have
> equipment capable of handling 192kHz sampling instead of 48kHz, then you
> might as well use it. If you are a professional recording studio, you
> want to use the absolute best that you can afford.
Not fully correct. That the higher sample rate must yield a more
fine-grained representation of the souce is true, but what matters is
being able to reproduce the source, which can be done as soon as the
sample rate match/exeed the minimum as required by Shannon/Nyquist + of
cause practical considerations WRT oversampling and filtering et al..
It can be shown by math, which I can understand - just don't ask me to
provide such math proof :)
> On the other hand, you can record at 44.1kHz and 48kHz and find that the
> quality of sound is exactly what you want. In fact, if you are going to
> distribute the music digitally on CD or compatible with a CD then you
> will be providing the listener with music sampled at 44.1kHz no matter
> what frequency you originally sampled it at. There is no advantage to
> 192kHz sampling and down converting to 48 over simply sampling at 48kHz
> in the first place.
Agreed. In fact, I've heard numerous stories about pro audio engineers
working in 44.1/48 and simply upsampling to 96/192 if clients require
this high sample rate. When getting the work back from the client, they
downsample again. With correctly applied up/down sampling, dithering
and noiseshaping, the result is reportedly indistinquisable.
> As for aliasing effects that were discussed, all A/D converters use an
> anti-aliasing filter before the actual conversion. This prevents beat
> frequencies from appearing in the audio. In fact, modern A/D converters
> use a two-step anti-aliasing filter that provides a very sharp cut off
> of the dangerous frequencies. So, you aren't going to hear beat
> frequencies in the result because the difference in frequency between
> the original signal and the sampling rate are large enough that the
> resulting aliases are outside of the audible rangle.
>
> Bob
Absolutely true.
--
rgds,
van Sinn