Subject: Re: [linux-audio-dev] RFC: API for audio across network - inter-host audio routing
From: Richard C. Burnett (burnett_AT_tality.com)
Date: Fri Jun 14 2002 - 18:35:45 EEST
Actually you are quite wrong about 192 kHz being a hype. Granted if you
are going back down to 44.1 you are not getting much of a benefit. But if
you are say creating music for SACD or DVDA formats, it is
essential. There are three problems caused by lower bit rates; greater
clock jitter distortion, non-linearities in the D/A, especially in
Delta-Sigma single bit converters, and the number of sample points of say
a 20khz audio signal. At 40Khz sampling that would give you 2 points on
the wave to reconstruct it. What if you're sampling intervals are 180 out
of phase with that signal? You would lose it completey. There are also
all sort of phase distortion problems at higher frequencies for the same
reason.
Now, let's take signal processing. Have you ever worked with video or
image files? A few of my professional friends work with this stuff
everyday. Their experience is to work in the highest resolution possible
for all image transforms and then scale down to what you need. The reason
is multiple signal processing techniques suffer the addition of round off
related distortion. In that I mean there are less points of interest in
the data and the result can and will be different in the end.
And to point out something about low-latency, if it really wasn't an
issue, people wouldn't be working on it for free. It's extremely
noticable to almost everyone I know.
Rick
On Thu, 13 Jun 2002, xk wrote:
> > There's a psychoacoustic phenomenon known as the Haas effect which states
> > that a direct sound and it reflections (echos) are percieved as a single
> > sound by the brain, where the time difference between the two is less than
> > about 30ms. So if the brain can't distinguish between sounds at this level
> I
> > think you'd get away with a 10ms delay in your instrument without the rest
> of
> > the band calling you names :-)
>
> How about the 1.0-1.5 ms latencies that everbody tries to obtain (or already
> has) in both Linux/Win world? That always made me wonder if this isn't just
> hype like the 192 kHz issue.
>
> I'm not a professional musician, but a 25 ms latency makes me more than
> happy.
>
>
>
>
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