[LAD] LADSPA extension for periodic control values?

Stefan Kost ensonic at hora-obscura.de
Fri Jun 19 19:10:02 UTC 2009

Stefano D'Angelo schrieb:
> 2009/6/13 Jörn Nettingsmeier <nettings at folkwang-hochschule.de>:
>> hi everyone!
>> sorry if this has been discussed before, but i didn't find anything in
>> the archives...
>> consider the case of periodic control values of LADSPA plugins, for
>> instance the azimuth in a horizontal panner or the phase shift in a phaser.
>> currently, they are usually marked as BOUNDED_BELOW and BOUNDED_ABOVE,
>> but the host has no way of knowing that the upper bound is next to the
>> lower bound, so that it can chose the shortest path to the next value
>> when interpolating automation control points.
>> take ardour, for example: if i want to spin a source 360 degrees, i have
>> to start at 0, set a control point at 180, set another control point at
>> the exact next sample to -180 and then onwards. if there is even a
>> single sample between the control points, the interpolation will cause
>> the image to jump in weird ways, because it doesn't know that 180 == -180.
>> does it make sense to add a new hint to LADSPA, something like
>> LADSPA_HINT_BOUNDED_ABOVE as well as the respective port range hints,
>> *and* imply that LowerBound is equivalent to UpperBound in the port
>> range hint structure.
>> this would enable hosts to do the Right Thing(tm).
> Hi,
> I think it makes no sense nowadays to do something like that, for two reasons:
> * LADSPA is old, hence old LADSPA hosts will not support that and
> new/maintained ones are not likely to support that, since many are
> focusing on newer APIs;
> * An LV2 extension would allow you to do that quite easily in LV2,
> which is probably preferable these days.
> That said, I can already hear people who disagree with me shouting and
> screaming.

I disagree. I would not mind adding support for more hints to the gstreamer
ladspa wrapper. Its not a lot of work and its good to have that now even if lv2
takes over in the long run.

The other think I'd like to have is hints for audio-port channel
grouping/mapping. That is describe that a port is the left-channel of stereo
pair named <xyz>, Even if this goes to the rdf.


> Stefano
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