[Kdenlive-devel] Questions about audio effects

Hugh Tebby hugh.tebby at gmail.com
Fri Jun 25 19:58:43 UTC 2010

Hi everyone,

I've listed all the audio effects that I have, and here's what I find :

Working perfectly:
- Declipper: I suppose it works... not sure how to test
- Vinyl
- Room reverb
- Pitch Scaler
- Pitch Shift
- Volume

Tweek needed:
- Equalizer: Not enough controls (8 ?), and vertical sliders would be better
- Gain: expecting dB instead of %, should be under "audio correction" folder
- Limiter: seems to work... but no idea what it really does (and what is the
release time ?)
- Mono to stereo: left to right only, options for right to left would be
- Mute: just gain effect with fixed gain to 0 and not modifiable (weird from
a user pov)
- Normalise: gain effect with fixed gain to 0, not modifiable and normalise
option activated (weird from a user pov)
- Phaser: Ok, but Rate doesn't seem to affect the sound
- Sox band: width OK, but Center Frequency doesn't work

Not usable:
- Sox strech: Window ok but too powerful, Factor does nothing. Sox
recommends using the Tempo effect instead of stretch
- Sox Pitch Shift: awful sound
- Sox Bass: awful sound
- Rate Scaler: Works but ugly (repeats every second or so ), user should be
able to change the 'segment' size (if possible)

No effect:
- Sox Echo
- Sox Flanger
- Sox Gain
- Sox Phaser
- Sox Reverb
- Sox Vibro
- Reverb

Propose that all non fonctionning or unusable effects be removed before the
next release (either blacklist or moving the xmls away into another folder
for the time being). I'll look into the "tweak needed" effects later on to
see if I can do something.

Unfortunately the LADSPA plugins website is down, so no documentation is
available for those effects...


2010/6/4 Hugh Tebby <hugh.tebby at gmail.com>

> Thanks for your answers Dan. I suppose I'l have to dive down the rabbit
> hole into MLT wonderland !
> I'll be looking into this in the next few weeks. Actually I think that even
> the simple first step of disabling effects that don't work at the moment
> would be quite useful, so I'll start off with that.
> 2010/6/3 Dan Dennedy <dan at dennedy.org>
> 2010/5/31 wille <wille.yyz at gmail.com>:
>> > Yes, left/right stereo balance.
>> >
>> > It would be very useful a feature that allow split a stereo audio clip
>> in
>> > two mono clips.
>> Well, now you have requested two different new features when Hugh was
>> volunteering to do some cleanup. The lack of balance/pan is already
>> well known and on my todo list. I praise Hugh's interest in
>> volunteering for some cleanup and would be saddened to see him
>> distracted.
>> One thing you can do today is to split the audio and video and add the
>> clip again on an audio track. Then, use the channelcopy filter on both
>> audio clips to isolate left vs. right. Finally, you can use the
>> keyframable volume effect on each to do panning. Unfortunately, today
>> channelcopy is exposed in Kdenlive as simply "Mono to stereo," but you
>> can alter the effect XML file for that to add "to" and "from" channel
>> parameters (0 is left, 1 is right). ("Mono to stereo" may seem like a
>> strange name, but it was added specifically for the case where a clip
>> only has a mono track and you do not want it both channels and not
>> just left.)
>> MLT and Kdenlive does not support the notion of a different number of
>> channels per track. So your second request is much longer term, if
>> ever, especially considering that I am still working on proper
>> multichannel (>2) support. I have been doing a lot with multichannel
>> in the past year for broadcast applications of MLT, but there are
>> still some gaps to add it in Kdenlive. One of these is surround
>> panning, which would also be capable of stereo.
>> > 2010/5/31 Hugh Tebby <hugh.tebby at gmail.com>
>> >>
>> >> Do you mean left/right stereo balance ? I don't think there's such an
>> >> effect available in Sox or Ladspa... Would probably have to be done
>> directly
>> >> with MLT...
>> That is correct.
>> >> 2010/5/31 wille <wille.yyz at gmail.com>
>> >>>
>> >>> By the way, I feel the need of a Balance audio effect or a similar
>> tool.
>> >>>
>> --
>> +-DRD-+
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