[gstreamer-bugs] [Bug 360246] [audioconvert] Optionally apply dithering

[GStreamer (bugzilla.gnome.org)]

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  GStreamer | gst-plugins-base | Ver: HEAD CVS




------- Comment #17 from Sebastian Dröge  2007-04-20 12:40 UTC -------
OK, I have everything almost finished, it only needs some polishing and harder
testing next week, then I'll attach a patch.

This will include a split of the pack functions into quantize and pack, 4
dithering modes (none, rpdf, tpdf and tpdf high frequency) and 4 noise shaping
modes (none, simple one-pole, medium 6-pole with David's coefficients, high
quality 20-pole with coefficients generated by dmaker for the most common
sampling rates and the one nearest to the current sampling rate is chosen).

Dithering is tpdf by default when target depth < source depth and target depth
< 20, noise shaping is disabled by default.
This decision is made because of the following reasons:
a) soundcards' AD converter currently only have a SNR up to something lower
than what 20 bit samples provide, thus the noise generated by the AD converter
is already higher than the noise that would be added by dithering and as such
adding dithering is useless (and would even add more noise).
b) high frequency tpdf and noise shaping should only be used on the conversion
step, otherwise (if used more than once one the same samples) it will cause
distortions.

Apps like buzztard for example would then use audioconvert with default
settings for everything but the last conversion and would use tpdf-hf and some
kind of noise shaping for the last conversion. The same could probably be done
for playbin too.


Whenever noise shaping is used audioconvert uses double as intermediate format
as otherwise the computation would become a bit ugly to impossible. For only
dithering or none of both the current intermediate formats are used and for
both disabled the results are exactly the same as before.


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