[Kdenlive-devel] pitch effects

Dan Dennedy dan at dennedy.org
Mon Sep 13 02:42:45 UTC 2010

On Sun, Sep 12, 2010 at 7:22 PM, Dan Dennedy <dan at dennedy.org> wrote:
> On Sat, Sep 11, 2010 at 11:54 PM, Alexandre Prokoudine
> <alexandre.prokoudine at gmail.com> wrote:
>> 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.
> works for me. the pitch lowers when below 100.
>> Rate Scaler. For some reason default value is 10, which in Kdenlive
> Kdenlive divides its value by 10 before passing it to LADSPA. This is
> how it provides float values. Other effect parameters may have
> different denominators.
>> 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.
> I get the same result as you, but it does the same thing that

I take that back. 10 in Kdenlive is normal and does not speed it up for me.

> standalone Jack Rack does when I route Kdenlive's output through Jack
> and Jack Rack and load rate_shifter_1417. However, MLT's LADSPA
> integration code is based entirely on Jack Rack. So, maybe there is a
> bug in Jack Rack that I inherited. Do you know of another tool similar
> to Jack Rack that makes it easy to try out LADSPA filters on Jack
> streams? Meanwhile, I will spend a little time with a WAV file and
> another tool that does LADSPA to get a comparison.

When I use Audacity and load the Rate Shifter, it sounds the same as
in Kdenlive. 1 is normal, not 0. 0 gives me silence in both Kdenlive
and Audacity.

>> Pitch scaler suffers from same bug as in Pitch shift: everything below
>> 100 means silence.
> This works for me as well - values below 100 are not silence.

Pitch scaler works the same for me when comparing Kdenlive, Jack Rack,
and Audacity. Same goes for Pitch shift.

What locale are you using?

>> 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
> They are named for their respective LADSPA plugins. I am of the
> opinion that we should use RDF to make all of them available.
>> 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.
> Those are completely different implementations not available through
> SoX or LADSPA, right? So, someone would need to implement that, and
> you sound like the right person to do it. :-)
>> Alexandre Prokoudine
>> http://libregraphicsworld.org
> --
> +-DRD-+


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