Subject: Re: Re[2]: [linux-audio-dev] peakfiles and EDL's
From: Richard C. Burnett (burnett_AT_tality.com)
Date: Wed Feb 28 2001 - 20:58:47 EET
I think there was mention of DC offset from plug-ins, where you may want
to observe a +/- DC offset which could could miss with an absolute
display. Mainly I would think this would be for tuning plugins or finding
errors in them. I cannot think of any advantage to a DC offset, only the
disadvantge of decreasing your dynamic range.
Rick
On Wed, 28 Feb 2001, Robert Schrem wrote:
> > > 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
>
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