[sdiy] Panning (again)

Tue Dec 22 15:59:17 CET 2020

(Hi Mark, nice to see you here!)
Based on my experience, Mark is right.  Douglas Self outlines the problem well.  As I remember the desired control curve isn't really based on an easily realized control law so linear or exponential responses don't really do it by themselves.
I'm mostly considered this in the context of crossfader design.
I've done a mastering grade 4x crossfader (for Salt Mastering) based on the THAT part and app note.  Worked well enough for that application.
For the Moog Matriarch I remember using a much simpler diode based piece-wise control signal for the x2164 for some volume control VCAs and another crossfader (maybe it was the wet/dry mix?).  That worked well for that circuit.
In pickier applications one could certainly go deep with this, probably better to use a LUT if you had a spare DAC channel laying around.
Ben
    On Tuesday, December 22, 2020, 05:19:16 AM EST, mark verbos <markverbos at gmail.com> wrote:  

 Douglas Self wrote pretty extensively about this in “Small Signal Audio Design” (very recommended), though mostly not voltage controlled.If you want to really go down the rabbit hole, start with a goal of using just a pair of VCAs to do level and panning on a mixer channel. Then ask yourself if you want to use exponential or linear VCAs. Then let the games begin. Serge did us the service of designing this type of thing for both kinds of VCAs (in his case a discrete Blackmer cell and a CA3280), so his circuits are a good jumping off point. That Corp makes an evaluation board for their THAT2162, which is a bit like half of a 2164 (exponential), they have a circuit that allows you to adjust the pan curve.
I worked with Michael Zähl on the "CV channel” for the AM1 high end mixing board. Since everything is voltage controlled, it has a LOT of VCAs. He became so specific about the curve of not just the panning, but the level control that he ended up adding a transistor pair logging circuit in the control path of each VCA to tweak the curve. And each of those has to be trimmed.
Mark

On Dec 16, 2020, at 12:17 AM, Tom Wiltshire <tom at electricdruid.net> wrote:

There’s a load of similar and useful circuits here, including dry/wet mixing:

http://www.geofex.com/Article_Folders/panner.pdf

==================
       Electric Druid
Synth & Stompbox DIY
==================

On 15 Dec 2020, at 19:35, Didier Leplae via Synth-diy <synth-diy at synth-diy.org> wrote:

Is there a simple way to do a similar circuit but reversed, like for a dry/wet pot? 

On Dec 15, 2020, at 12:38 PM, David G Dixon <dixon at mail.ubc.ca> wrote:

Hey Team, I've been thinking about this panning thing, and I came up with the following very simple pot-based panning circuit: <SimplePanner.png> The gain responses of this circuit are shown below, and compared with sin and cos responses: <PanPlot.png> I believe that I can create a voltage-controlled version of this simple pot panning circuit fairly easily by replacing the pot with a pair of modified Irwin 2164 circuits.  I did this for the Morphing LFO. Would this response suffice as an "equal power" panner?_______________________________________________
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