Re: Digital vs. Analog

[P3D Peter Davis <pfd@xxxxxxxxxxx>]

> The main thing to keep in mind is the resolution capability of the
> receiving system.  As a general rule, for example, people can not
> hear the difference between an analog sound and its sampled sound
> (sampled at 44.1 kHz) if the D/A converter is good (i.e. accurate
> with smoothing filters, though the smoothing filters should not
> actually be necessary, either, because the harmonics are all beyond
> human hearing.)  Anyhow, there are no 'gaps' between the samples in
> a reconstructed sound.  The difference in noticed in sound (the
> "warmth" of vinyl, for example) is actually due to artifacts
> introduced along the path of recording, manufacturing, and playback,
> and can be convincingly simulated with DSP techniques.  CDs of
> albums previously released on vinyl sound different ("cleaner" or
> "harsher") because many of these steps are eliminated.

My understanding is that higher frequencies, although inaudible in the
"real" world, will show up as aliases unless filtered.  Ideally, this
would be accomplished with a brick wall filter, which completely
removes everything above 22.05 kHz (since, by Nyquist principles, the
sampling rate must be double the highest sampled frequency), but
leaves intact everything below.  In practice, however, there are no
such ideal filters.  They all have a sloping curve which attenuates
some audible signal, and leaves in some of the "inaudible" frequencies
present as aliases.

Of course, I could be mistaken.

-pd


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