[LAD] panning thoughts

Ralf Mardorf ralf.mardorf at alice-dsl.net
Fri Nov 12 16:19:45 UTC 2010

On Fri, 2010-11-12 at 15:47 +0000, Rui Nuno Capela wrote:
> On 11/12/2010 03:08 PM, Eric Kampman wrote:
> > Thanks. I don't understand the square root though. The equation is even
> > more expensive processor-wise than the straight cos.
> > 
> the SQRT2 is a constant := sqrtf(2.0f), usually defined as M_SQRT2 in
> "math.h"
> qtractor computes the panning coefficients each turn they get changed.
> then it applies through regular gain to each steaming channel as usual.
> just const mul over a vector/block/buffer, whatever
> > Granted, you're quoting someone else, but maybe someone out there knows.
> i'm no expert but i'm sure Ralf quoted me :)

Hi Eric :)

you asked for the reason, why it's "wanted" to do this "cycles wasting"

So first me, than this particular Rui ;):

"On 01/25/2010 01:19 PM, Ralf Mardorf wrote:
>    * Panning for mono tracks, resp. balance for stereo tracks. The
>      "approximated equal-power effect" should cause nearly no
>      difference for the loudness of signals that are entirely to the
>      left or right, while other signals are in the centre, when
>      listening to a stereo mixing on mono. The relation of the signals
>      nearly should be kept. Is this right?

right. stereo panning in qtractor follows an "approximated equal-power"
trigonometric formula: L = SQRT2 * cos(pan * PI/2); R = SQRT2 * sin(pan
* PI/2), where pan value ranges from 0 (full-left) to 1 (full-right).

I still could nag a lot about some issues I don't like regarding to
Linux audio, especially regarding to MIDI ;), but I never noticed any
issue regarding to panning for any app. Qtractor does a good panning.

Resume: Audio engineers wish to have this loudness compensation, to
avoid fading after panning ;).

2 Cents,


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