David T. Lewis uploaded a new version of Sound to project The Inbox:
http://source.squeak.org/inbox/Sound-dtl.67.mcz

==================== Summary ====================

Name: Sound-dtl.67
Author: dtl
Time: 10 December 2019, 10:51:04.985835 pm
UUID: ca970845-8428-41f9-b83c-f64a6cc732c1
Ancestors: Sound-eem.66

Sound mixing improvements by Stéphane Rollandin (spfa).
Allow adjusting volume of mixed sounds while playing. 
Original discussion at http://forum.world.st/Adjusting-the-volume-of-a-sound-as-it-s-playing-td5102562.html
Patches posted to squeak-dev at http://lists.squeakfoundation.org/pipermail/squeak-dev/2019-December/205440.html

=============== Diff against Sound-eem.66 ===============

Item was changed:
  ----- Method: AbstractSound>>loudness (in category 'volume') -----
  loudness
  	"Answer the current volume setting for this sound."
  
+ 	self hasVolumeEnvelope ifTrue: [^ self volumeEnvelope scale].
+ 
+ 	^ scaledVol asFloat / ScaleFactor!
- 	^ scaledVol asFloat / ScaleFactor asFloat!

Item was changed:
  ----- Method: MixedSound>>mixSampleCount:into:startingAt:leftVol:rightVol: (in category 'sound generation') -----
  mixSampleCount: n into: aSoundBuffer startingAt: startIndex leftVol: leftVol rightVol: rightVol
  	"Play a number of sounds concurrently. The level of each sound can be set independently for the left and right channels."
  
  	| snd left right |
  	1 to: sounds size do: [:i |
  		(soundDone at: i) ifFalse: [
  			snd := sounds at: i.
+ 			left := (leftVol * (leftVols at: i) * scaledVol / ScaleFactor) // ScaleFactor.
+ 			right := (rightVol * (rightVols at: i) * scaledVol / ScaleFactor) // ScaleFactor.
- 			left := (leftVol * (leftVols at: i)) // ScaleFactor.
- 			right := (rightVol * (rightVols at: i)) // ScaleFactor.
  			snd samplesRemaining > 0
  				ifTrue: [
  					snd mixSampleCount: n into: aSoundBuffer startingAt: startIndex leftVol: left rightVol: right]
  				ifFalse: [soundDone at: i put: true]]].
  !

Item was changed:
  ----- Method: RepeatingSound>>mixSampleCount:into:startingAt:leftVol:rightVol: (in category 'sound generation') -----
  mixSampleCount: n into: aSoundBuffer startingAt: startIndex leftVol: leftVol rightVol: rightVol
  	"Play a collection of sounds in sequence."
  	"(RepeatingSound new
  		setSound: FMSound majorScale
  		iterations: 2) play"
  
  	| i count samplesNeeded |
  	iteration <= 0 ifTrue: [^ self].
  	i := startIndex.
  	samplesNeeded := n.
  	[samplesNeeded > 0] whileTrue: [
  		count := sound samplesRemaining min: samplesNeeded.
  		count = 0 ifTrue: [
  			iterationCount == #forever
  				ifFalse: [
  					iteration := iteration - 1.
  					iteration <= 0 ifTrue: [^ self]].  "done"
  			sound reset.
  			count := sound samplesRemaining min: samplesNeeded.
  			count = 0 ifTrue: [^ self]].  "zero length sound"
  		sound mixSampleCount: count
  			into: aSoundBuffer
  			startingAt: i
+ 			leftVol: leftVol * scaledVol // ScaleFactor
+ 			rightVol: rightVol * scaledVol // ScaleFactor.
- 			leftVol: leftVol
- 			rightVol: rightVol.
  		i := i + count.
  		samplesNeeded := samplesNeeded - count].
  !

Item was changed:
  ----- Method: SequentialSound>>mixSampleCount:into:startingAt:leftVol:rightVol: (in category 'sound generation') -----
  mixSampleCount: n into: aSoundBuffer startingAt: startIndex leftVol: leftVol rightVol: rightVol
  	"Play a collection of sounds in sequence."
  	"PluckedSound chromaticScale play"
  
+ 	| finalIndex i snd remaining count leftScaledVol rightScaledVol |
- 	| finalIndex i snd remaining count |
  	currentIndex = 0 ifTrue: [^ self].  "already done"
+ 
+ 	leftScaledVol := leftVol * scaledVol /// ScaleFactor.
+ 	rightScaledVol := rightVol * scaledVol /// ScaleFactor.
+ 
  	finalIndex := (startIndex + n) - 1.
  	i := startIndex.
  	[i <= finalIndex] whileTrue: [
  		snd := (sounds at: currentIndex).
  		[(remaining := snd samplesRemaining) <= 0] whileTrue: [
  			"find next undone sound"
  			currentIndex < sounds size
  				ifTrue: [
  					currentIndex := currentIndex + 1.
  					snd := (sounds at: currentIndex)]
  				ifFalse: [
  					currentIndex := 0.
  					^ self]].  "no more sounds"
  		count := (finalIndex - i) + 1.
  		remaining < count ifTrue: [count := remaining].
+ 		snd mixSampleCount: count into: aSoundBuffer startingAt: i 
+ 			leftVol: leftScaledVol
+ 			rightVol: rightScaledVol.
- 		snd mixSampleCount: count into: aSoundBuffer startingAt: i leftVol: leftVol rightVol: rightVol.
  		i := i + count].
  !