[LAD] AMS to Ingen: VC to PCM

David Robillard d at drobilla.net
Sun Sep 25 21:01:30 UTC 2011

On Sun, 2011-09-25 at 14:28 +0100, Aurélien Leblond wrote:
> >1. Audio in/out ports. These are just blocks of samples, same
> >   as e.g. Jack buffers. Some call this 'PCM' but that is a
> >   misnomer.
> >
> >2. Control in/out ports. These are technically identical to
> >   audio ports (full sample rate), but the signals carried
> >   on them are normally not meant to be audio. How they are
> >   interpreted depends on the module and the particular port.
> >   Frequency control inputs can be linear or log, in the latter
> >   case that means 1/octave. Gain controls can be linear or log,
> >   there is AFAIK no fixed conversion factor for the latter. For
> >   example the VCA module uses 80dB/1 in exponential mode, but
> >   other gain controls may be different.
> >
> >   Control ports are audio rate, but most modules/plugins subsample
> >   some or most of them. They either just use the first value in a
> >   block, or recompute internal paramters based on the last value
> >   in a block and then interpolate them linearly.
> >
> >   Since control signals are (at least officially) at audio rate,
> >   LADPSPA plugins designed to be used in AMS (e.g. mine) will
> >   declare their control inputs as audio inputs.
> Thanks, I think it makes things way clearer!
> What's confusing me so far is that I ported the VCO2 module, but with
> exactly the same setup, the VCO2 LV2 in Ingen sounds out of tune
> compared to the one in AMS. I thought it was due to some kind of
> needed convertion, but maybe I'll go back to my code to double check I
> didn't make any mistakes!

The note builtin in Ingen uses Hz for frequency. Anything else is
completely insane :)

There is a converter plugin in 'omins' which I need to port to LV2 as
well one of these days...


More information about the Linux-audio-dev mailing list