Since we are dicussing MixedSound, I have a proposal, currently 
implemented in muO, for a better panning, by using a -4.5 dB pan law as 
explained here:
http://www.cs.cmu.edu/~music/icm-online/readings/panlaws/index.html


So I propose in MixedSound

add: aSound pan: leftRightPan volume: volume
	"Add the given sound with the given left-right pan, where 0.0 is full 
left, 1.0 is full right, and 0.5 is centered. The loudness of the sound 
will be scaled by volume, which ranges from 0 to 1.0."

	|  vol |

	vol := (volume max: 0.0) min: 1.0.
	sounds := sounds copyWith: aSound.

	(self class panValuesFor: leftRightPan) allIn: [:leftPan :rightPan |
		leftVols := leftVols copyWith: (leftPan * vol) rounded.
		rightVols := rightVols copyWith: (rightPan * vol) rounded]


where, on the class side, we have

panValuesFor: aPos

	"aPos ranges from 0.0 to 1.0 (Squeak convention)"

	^  (MusicMachine db45PanAt: (aPos * 2) - 1) collect: [:ea |
		((ea * ScaleFactor) rounded max: 0) min: ScaleFactor]


The MusicMachine class is in muO, so it would have to be refactored 
here. The code is

db45PanAt: pNumber

	"pNumber ranges from -1 (45 degrees left) to 1 (45 degrees right)"

	"Uses -4.5 dB pan law
ref: http://www.cs.cmu.edu/~music/icm-online/readings/panlaws/index.html"

	| theta |

	theta := (pNumber + 1) * Float pi / 4.

	^ {
		"left" (theta cos * (Float halfPi - theta) / Float halfPi) sqrt.
		"right" (theta sin * theta / Float halfPi) sqrt
	}


Stef