[Kdenlive-devel] pitch effects

[Alexandre P. <ale...@gm...>]

Hi,

I was going through rather amusing inherited translation of pitch
related audio effects and noticed that the actual implementation is
quite broken.

Pitch shift is OK, except below 100 you get the same sound, whatever
value you use. This is really not reproducible with the original AM
pitchifter LADSPA plug-in. Above 100 it works as expected though.

Rate Scaler. For some reason default value is 10, which in Kdenlive
corresponds to normal playback. However the original Rate Shifter
LADSPA plug-in doesn't work like that. It has a range of values
between -4 and 4, and 1 (10 in Kdenlive) corresponds to actually
speeding audio up. If you dive a bit further, you'll find out that 0
in LADSPA corresponds to no changes, whereas in Kdenlive zero
corresponds to no sound at all. No, wait, I can hear clicks :)
Finally, with negative values sounds goes backwards as expected.

Pitch scaler suffers from same bug as in Pitch shift: everything below
100 means silence.

So, I really don't know who to blame -- Kdenlive or MLT. Please tell
me which bug tracker to poison with this report :)

Also, I'm not entirely sure it makes a lot of sense to have plug-ins
with such names and functionality. Being an Audacity user for almost a
decade I'm sort of addicted to names and functionality like "Change
Speed/Pitch/Tempo". Audacity's implementation relies on libsamplerate
which works rather well. the application also makes a good use of
SBSMS library that works really well with any kind of sound, but
unfortunately is not entirely good for real-time processing. Now,
RubberBand is a rather good choice for RT, but reportedly has its
limits in terms of quality when it comes to something other than
percussion. Don't know if that's of any use to you.

Alexandre Prokoudine
http://libregraphicsworld.org