Subject: Re: Re[2]: [linux-audio-dev] peakfiles and EDL's
From: Robert Schrem (Robert.Schrem_AT_WiredMinds.de)
Date: Wed Feb 28 2001 - 19:55:45 EET
> > Well I think you need only to compute one peak value for a
> > sample data block: Max = abs(all samples for a block)
> > I still don't understan what information we gan if we compute
> > seperate min and max peak values.
>
> But what about waveforms that have a certain DC offset? (That's SoundForge
> spead, but Steve Harris used the same term for one of his LADSPA plugins,
> so I believe it's commonly used). There is no guarantee that a waveform is
> well-balanced over the zero axis, so you might find cases where the
> positive part is well within ranges while the negative part is already
> clipping.
<ExtensiveExplainMode DetailLevel="max">
DC offset stands for 'direct current' offset
(AC means 'alternating current' - AC/DC, the band name
formed from this :)
It means that all samples have a constant drift in
one direction - often a result of a drifting reverence
voltage source inside the AD converter's circuit.
This was an issue with older AD converters: Even if you
short circuit the input of the AD the converter it
would still not output 0 values as expected - instead
they delivered a small value that even changed with the
temperature of your equipment.
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>
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.
robby
This archive was generated by hypermail 2b28 : Wed Feb 28 2001 - 20:33:26 EET