Support for sequencing JACK/LV2 CV?

[mxmilkiib]

Both JACK and LV2 support CV signals for finer-than-MIDI automation. More recently, carla-git has started supporting CV internally and zrythm-git has added CV support. Being able to sequence CV in ossia score would allow for some neat opportunities.

In the LV2 spec and Ingen paper:

• http://lv2plug.in/ns/lv2core/#CVPort
• https://lac.linuxaudio.org/2015/papers/24.pdf - see section 2.4

Host commits:

• http://git.drobilla.net/cgit.cgi/ingen.git/log/?qt=grep&q=cv
• https://github.com/falkTX/Carla/search?q=cv&type=Commits

Plugins with CV support so far:

• https://github.com/blablack/ams-lv2
• https://github.com/harryhaaren/avw.lv2
• http://drobilla.net/software/blop-lv2
• https://github.com/ssj71/infamousPlugins
• http://drobilla.net/software/fomp - some of

lad on Freenode IRC if you're so inclined.

[jcelerier]

Hello, good idea, adding it to the roadmap :-) won't be hard to implement in ossia score since the internal control rate is already at audio rate

[mxmilkiib]

More info on https://linuxmusicians.com/viewtopic.php?f=1&t=20701

[mxmilkiib]

Just to clarify, this would be enabled through support for JACK port metadata.

[jcelerier]

hm, so we would create (or detect) the jack CV ports available in other software, and make them available to connection to LV2 "CV" ports ?

One thing I'm surprised is - the JACK doc seems to say that they shouldn't be exposed as audio outputs, but isn't a big point of CV to also send it to e.g. a hardware modular synth through actual sound hardware ? (or also use audio data as a control ?) (pinging @jln- as a modular reference person :p)

[mxmilkiib]

CV shouldn't be routed to a speaker, I believe that's what that msg was trying to communicate.

The CV propriety can be used to indicate in a graph what ports are expecting a CV (i.e. possibly DC at times) signal. It could also be used to allow further forms of UX.

Edit: a CV generator can produce an AC audio rate signal that is of the form of an audio wave which can be routed to a speaker, but DC signal to a speaker is bad.

[jln-]

(pinging @jln- as a modular reference person :p)

:-D Indeed, sending DC voltage can cause damages. That's why most soundcards filter out DC to prevent this (and thus cannot be used to control modular synth).

But a few soundcards do not (Motu being main, not to say only, example).

[mxmilkiib]

I'm not sure what mechanism is used to see what ports other JACK clients have available.

To mark JACK outputs as CV, the signal-type metadata keyvalue is used.

[mxmilkiib]

The "Linux / BSD" label is not really on the mark, as both LV2 and JACK are multiplatform. An "Enhancement" tag would be nice though.

[jcelerier]

hm, in the software, how would marking a port available as jack CV be most meaningful ? should it be for instance a new separate device ?