Subject: Re: Re[2]: [linux-audio-dev] peakfiles and EDL's
From: Frank Neumann (franky_AT_viona.de)
Date: Wed Feb 28 2001 - 20:42:24 EET
Hi again,
Robert Schrem wrote:
> <ExtensiveExplainMode DetailLevel="max">
[...]
> As far as i know this isn't a issue for some years now -
> the today converters are more sofisticated and don't produce
> DC offsets. They have digital high pass filters built
> inside (with very low filter frequency). This avoids that
> any constant offset will be output by the converter.
> (This also means, that you can't measure DC voltages directly
> with an AD converter build for audio purposes).
> </ExtensiveExplainMode>
Thanks for that nice historical explanation. Still, I did stumble across some
cases of files with DC offset here and there - you know, I'm sometimes out
hunting for drum .wavs on the 'net, and at times I wonder why files that I
play stop with a "click" though their end clearly does a fade to 0.
I wrote a tiny tool for myself to check, and found that some of them were a
good deal off from the 0 point. Good to have a DC offset corrector handy
then!
> Anyway: Even if you would care about DC offset you would
> still recognize ANY clipping if we only compute the
> absolut maxima of an set of samples. For positive signed
> samples as well as for negative signed ones.
Hmm..I might have misunderstood your definition of "maxima" here. I simply
think of "maxima" as "largest positive value in range" and "minima" as
"smallest negative value in range". Only looking at the largest positive
values then would not show me when a negative value hits the bottom of my
signal range.
Now I understand your idea is to do "abs(x)" for all samples in the range,
at the same time storing the max value of these, and then only plotting the
"positive half" of the samples. Ok, got it :-). Maybe people are just more
used to finding a peak representation of a waveform that looks like the
original waveform - with values both above and below zero.
(Someone tell me when I'm making a fool out of myself here :-),
Frank
This archive was generated by hypermail 2b28 : Wed Feb 28 2001 - 21:22:39 EET