[Lmuse-user] Pan (mono tracks) vs. balance (stereo tracks): Both incorrect in MusE?

[Tim E. R. <ter...@ro...>]

Hey.
I'm working in the audio mixing engine again.

I'm finally adding sample-accurate track controllers
 such as volume and pan. The code also demonstrates the place 
 to inject sample-accurate faders and cross-faders when we 
 get around to adding them.

I've noticed that we do possibly incorrect things with the pan control.

Our pan knob goes from -1.0 to 1.0.
The pan formula we use is:

  vol_L = _volume * (1.0 - _pan);
  vol_R = _volume * (1.0 + _pan);

 where _volume is the volume fader value, _pan is
 the pan knob value. vol_L and vol_R are the factors 
 that are applied to (multiplied by) the audio data values. 
In the case of a mono track, this is how much of the signal is
 applied to the L and R right outputs. In the case of a stereo
 track, this is how much of each of the L and R signals are
 applied.
 
You can see that for a mono track, when 'pan' is in the center,
 100% of the signal is applied to the L and R, and when the knob is 
 turned to full L or R, it actually *increases* the L or R to twice the 
 value, +3dB (power), while decreasing the other channel to zero of course.

According to places like wikipedia, when pan is at center, the L and R
 outputs should be, depending on the chosen Pan Law [1], around 
 3dB to 6dB *lower* than when pan is at full L or R. 
4.5dB is a common compromise between the 3dB and 6dB.

So we're apparently doing this wrong by increasing the values
 *above* 0dB at pan extremities.

The situation for stereo tracks is apparently even worse.
In the case of stereo tracks the 'pan' knob should really be called
 a 'balance' control. And we are therefore not computing balance 
 correctly, according to [2]. We are applying these vol_L and vol_R 
 factors to the two channels, which is wrong - it needs to operate
 like a balance control.

Anyone have any objections to me attempting to fix this?

Also, I'm reading about mixers and Pre Fader Listening buttons trying 
 to understand if our button is working correctly, and if it might be 
 desirable to embellish the mixer strips with an extra pre/post button
 or two, or some other small handy button goodies.
Apparently PFL is used in conjunction with monitor buses, but
 in MusE tracks are so generalized that we don't have a 'monitor' bus. 
But we have 'Aux' tracks using aux 'buses', if you want to call them that.
Someone a long time ago added a 'monitor' buffer to our Audio Output tracks, 
 but it is totally unused and I'm thinking of removing it - but maybe not? 
Can we utilize this, and how do you think a 'monitor' feature in general 
 should work, behave, and appear in MusE, if at all, or are Aux tracks good 
 enough and just stick to making them better with a few pre/post buttons 
 and so on?

I know it might be desirable to allow effects after the fader so that
 for example reverb 'tails' will still sound, but for now until such features 
 are added I'm reasoning that such operations should be done with the 
 (reverb) plugin's level controls and the track volume fader really should 
 cut off *all* sound as it does now, after all it is a /track/ fader...

Cheers.
Tim.

[1] 
http://en.wikipedia.org/wiki/Pan_law
[2]
 http://www.rane.com/par-b.html#balance