[LAD] AMS to Ingen: VC to PCM

[Gabriel Beddingfield]

On 09/25/2011 05:10 AM, Fons Adriaensen wrote:
> On Sun, Sep 25, 2011 at 09:52:23AM +0100, Aurélien Leblond wrote:
>
>> I'm porting the AMS internal modules to LV2 plugins to be used in Ingen.
>>
>> Small problem is, AMS uses VC (even the output of the VCOs that
>> produce sound) when Ingen uses PCM...
>
> ?? You seem to be confusing some things.
[snip]
>
> 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
[snip]
>
> 3. Input ports corresponding to GUI widgets. These are control rate,
>     read once per block. They can be int or float. For continuous values
[snip]

And I think part of the confusion is that LV2 calls #3 a "control port", 
and doesn't currently have anything like #2.

On 09/25/2011 03:52 AM, Aurélien Leblond wrote:
 > So far, my research seems to lead that a simple multiplication by 16
 > of the VC output should convert it to PCM, and vice-versa.
 > That doesn't seem right though, as I would think the sample rate
 > should be involved in this conversion!

If your the same dude I met on IRC doing this exact same thing... you 
misunderstood what was said about 16.  I was saying that[1] I've heard 
that sometimes people implement CV ports at 1/16th the audio sample 
rate.  However it's simpler to just stick with the audio sample rate.

Also, in old-style analog synths the CV signal correspends to 1 
Volt/octave and has a range (0.0, +inf).[2]  In contrast, floating point 
audio has a range of [-1.0, 1.0].  There is no relationship between a 
control voltage signal (e.g. the position of a fader) and a PCM audio 
signal.

-gabriel

[1] ...based on my understanding of some discussions here
[2] http://en.wikipedia.org/wiki/CV/Gate