[Kdenlive-devel] Questions about audio effects

Tue Aug 31 16:37:26 UTC 2010

2010/8/31 Hugh Tebby <hugh.tebby at gmail.com>:
> Hi,
>
> With the 0.7.8 release approaching, I think the non functionning audio
> effects should be removed. In fact, according to the list I made it seems
> that most problems come from the Sox audio effects. It could be an issue
> with the sox plugins I have on my computer, but if it isn't I would suggest
> deactivating all sox plugins for the time being (along with Reverb and Rate
> Scaler which don't seem to work).
>
> Does anyone disagree with this ?

I disagree because the sox effects work for me, and you presented this
as all-or-nothing proposition. I was testing all audio effects
recently when I added pan and balance, and I remembered this email.
However, I did not undertake a rigorous study, but I was left with the
impression that nearly all of them worked as expected although some do
have dubious value. And there was only a couple that just did not seem
to work correct at all. For example, ones that have anything to do
with time such as stretch do not work correctly. I will do a more
thorough review of them as well as the history of this thread and get
back to you.

> Cheers,
> Hugh
>
> PS : and congrats everyone for the amazing work that has gone into Kdenlive
> (and the website !) these last months !
>
> 2010/6/25 Hugh Tebby <hugh.tebby at gmail.com>
>>
>> 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
>> good
>> - 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...
>>
>> Cheers,
>> Hugh
>>
>> 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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>>>
>>
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-- 
+-DRD-+