[linux-audio-user] Piano feedback, again bundled

[R Parker]

> 
> > > Try to explain to me what the use is of 96 Khz
> samples ? It's just
> > > marketing nothing more.. 48 Khz makes it
> possible to represent up to
> > > 24 Khz of sampled frequencies, far about what
> you can hear.
> > Ok, I'll have a go :-)
> > If you sample at 48Khz you need to filter out
> everything above 24Khz in
> > order to avoid alias noise. First of all this is
> not *really* possibkle,
> > filters don't block thay damp. Secondly a filter
> steep enough to let
> > ninimal amounts of energy through above 24Khz will
> be distorting the
> > upper part of the frequency range.Now if you
> sample at 96Khz the story
> > is the same, but not you have an extra octave to
> filter smoothly.
> > Another part of the story is that although a 48Khz
> sample can represent
> > frequencies upto 24Khz, the representation of the
> higher frequencies not
> > accurately describing the intensity.
> 
> Let's put it this way.. Do you think a CD sounds bad
> ? I think the average
> person can't hear much about 18 Khz (could be 20 Khz
> though).. So unless you
> are a sampler yourself you probably won't notice. I
> certainly won't go above
> 48 Khz since bigger is not always better.. Of course
> a lot depends on what
> sampler was used to capture the sound. 44 Khz could
> be an option but I'll
> have to have a look at the softsynths and hardware
> Grandest Piano will
> eventuelly be aimed at.

Assuming the average person can't hear above 20khz the
following argument, from the sox man page,
demonstrates why it's important to work with the
highest available clock.

The  Nyquist  frequency is equal to (sample rate / 2).
 Logically, this is because the A/D converter needs at
least 2 samples to detect  1  cycle  at the  Nyquist
frequency.  Frequencies higher then the Nyquist will
actually appear as lower frequencies to the A/D
converter and is  called  aliasing. Normally,  A/D 
converts run the signal through a highpass filter
first to avoid these problems.

I guess the interesting problem is aliasing. Right?

I'm not saying I know what's going on in digital audio
but it's an interesting set of challanges that I like
to learn about in order to improve my production
strategies. We need a 28 hour day.

Ron

> Roel / Utopia Sound Division
> http://www.utopiasd.com

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