[sdiy] SSM2164 VCAs

[Scott Juskiw]

With regards to the lin/log argument for VCAs, I don't think it's a  
good idea to assume that straight line envelopes should always feed  
log VCAs. I believe you should do what "sounds" best. Particularly  
with log VCAs, there are instances where 10db/volt works well, and  
other instances where 20 db/volt works well, or something in between.  
I built some VCAs that support both linear and log inputs at the same  
time which I find quite handy when I want to get really picky about  
envelope shape. Scroll down to the bottom of this page and listen to  
the two panning examples. One is 100% linear input, the other is 100%  
log input (with 16db/volt response IIRC).

http://www.tellun.com/motm/diy/tln132/TLN-132.html

In both cases a triangle wave (very linear 0-5 volts) is used to  
modulate the VCA amplitude. The results are quite different for the  
linear and log cases. If I was using this in a recording I'd probably  
use a mixture of 80% linear with 20% log.

On 8-Jun-09, at 10:25 PM, David G. Dixon wrote:

> Thanks Dave, Aaron and Tim for their excellent advice and links.  It  
> would
> appear that the Irwin-Gallo-Lamm-Bareille axis is all I need to go  
> forth and
> amplify!  It's interesting that the Irwin method of linearizing the  
> 2164
> appears to be very similar to the Sims method for linearizing the  
> 13700....
>
> To answer Tim's concern, I was going to put in switches to have the  
> option
> of linear or log response, for the very reasons you alluded to (analog
> envelopes should feed linear VCAs, and triangles (such as my lovely  
> triple
> LFO) should feed log VCAs).
>
> Now I've got to go and study (and possibly simulate) both Sims' and  
> Irwin's
> schemes to convince myself that I really understand what the heck is  
> going
> on there, and to determine whether it's strictly necessary for VCA
> applications and therefore justifies doubling the IC requirements.
>
> Cheers,
> Dave