Re: [linux-audio-dev] Dithering idiots

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Subject: Re: [linux-audio-dev] Dithering idiots
From: Paul Davis (pbd_AT_op.net)
Date: Mon Jun 17 2002 - 17:59:52 EEST


>On Mon, Jun 17, 2002 at 02:27:29PM +0100, Richard Bown wrote:
>
>> And where does "peak data" come into things then? Are those peak files that
>> an audio app produces the stored result of this interpolation or is that
>> something different? And if so, again, why?
>
>peak data is a precomputed representation of the min and max points of
>blocks of the original audio. it alleviates the need for reading large
>amounts of data where you are viewing for example 10 minutes of audio, etc.
>and each pixel represents a large number of samples.

it doesn't *have* to be pre-computed. if you take a look at David
Bartold's GtkWaveView widget, he computes peak data on the fly. Ardour's
GtkCanvasWaveView does this too when the resolution drops below the
peakfile frames-per-pixel level. i think snd does this as well.

>> soundforge seems to allow only powers-of-two scales, and creates a
>> peak file 1/128th the size of the original; it also has nice smooth zoom
>> in/out, and scrolling.

ardour is using 256 frames/pixel right now. until recently, we used
2048, and that caused major redraw delays when zooming in to the range
between about 128 and 2048 because it was necessary to read a large
amount of raw audio data to draw the waveform. we still haven't
decided on the optimal frames/pixel ratio yet.

--p


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