Subject: Re: Frequency response was Re: [linux-audio-user] Audiophile CD's
From: Jörn Nettingsmeier (nettings_AT_folkwang-hochschule.de)
Date: Mon Jan 28 2002 - 23:53:56 EET
Tony Lambley wrote:
>
> > > What happens when you sample a 1Hz sine with 2 samples a second, and
> those
> > > samples happen to coincide with the zero crossover points?
> >
> > That's why it's necessary to sample at f > 2b -- information is lost
> > when there isn't a sample close enough to the peak/trough of the wave.
> > I'm not sure how much greater than 2b f has to be, but apparently others
> > have determined that 44.1khz or 48khz is high enough to reproduce
> > frequencies up to 20kHz.
>
> But doesn't that still leave a huge potential loss of information? Our ears
> can't tell the difference between a sine and square at 20k, so a 44.1k or
> 48k sample rate is sufficient for a human intended audience.
you can't, because anything other than sine has overtones, which
would be well above our hearing range.
> Wouldn't fx algorithms be a difference case though?
not until there is downward aliasing or differential (*) tones. but
i can't think of any hi-fi applications that would make use of
aliasing or a case where you might have two sounds in the ultrasonic
which beat in the audible range.
you might argue that ultrasonics might cause the reproduction chain
to behave interestingly, but then again we can't directly hear the
high stuff, only what's transformed back into hearing range by
imperfect speakers etc.
(*) is this the correct term ? i'm thinking of f(beat) = abs(f1 -
f2) or ring modulators.
-- Jörn Nettingsmeier home://Kurfürstenstr.49.45138.Essen.Germany phone://+49.201.491621 http://spunk.dnsalias.org http://www.linuxdj.com/audio/lad/
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