Subject: Re: [linux-audio-dev] Dithering idiots
From: Bill Bland (@netpd.com)
Date: Mon Jun 17 2002 - 14:30:54 EEST
On Mon, Jun 17, 2002 at 06:55:22AM -0400, Paul Davis wrote:
[snip]
> >When generating a graphical preview of an audio file at various different
> >resolutions you obviously get slightly different pictures of the same
> >envelope depending on how you extract and interpret the sample information
> >at the dithering resolution you require.
[snip]
> i don't quite get it. when you render a waveform on the screen, you're
> normally not doing anything like interpolation. you're subsampling the
> amplitude waveform to a given frames-per-pixel density. i don't see
> how you can end up with different pictures of the envelope, except
> that the location of a given peak will shift slightly back-and-forth
> as you move in and out.
Probably wrong, irrelevant, or both, but I was thinking: Plotting a
waveform is like sampling it, and at certain sampling frequencies you will
get strange effects. Say you have a waveform representing a 1Hz sine
wave, and you sample it at 1Hz. Then you could draw the waveform on the
screen as complete silence, or a constant DC, when in fact that's a rather
misleading picture to draw.
Obviously if 1 pixel == 1 sample, you won't get this effect, but if you
zoomed out enough that 1 pixel == 44100 samples (for example), then you
could see complete silence (or an arbitrary DC value).
Just a thought. Correct as necessary ;)
Best wishes,
Bill.
-- Dr. William Bland. Microsoft makes simple tasks easy and complex tasks impossible. Sometimes it makes the simple tasks impossible too.
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