Hi Levente, Hi Stef,

On Sat, Sep 19, 2020 at 4:47 AM Levente Uzonyi <leves at caesar.elte.hu> wrote:

> Hi Eliot,
>
> On Fri, 18 Sep 2020, Eliot Miranda wrote:
>
> > Hi All,
> >
> >      the SampledSound>>#mixSampleCount:into:startingAt:leftVol:rightVol:
> method looks to be badly broken.  I don't understand the index scaling
> (yet) so I thought I'd throw this out there and see if anyone can spot when
> and
> > why this broke.
> >
> > Here's a simple example that generates a second long A below middle C
> (220Hz), smoothing start and stop, and then plays it, so far so good:
> >
> > | samples sineTable sound |
> > "1 second of A below middle C (220Hz). 16000 / 220 is 72.72 recurring"
> > sineTable := SoundPlayer sineTable: 73.
> > sineTable doWithIndex: "And let's not deafen anyone..."
> > [:sample :index| sineTable at: index put: sample // 4].
> > samples := SoundBuffer new: 16000.
> > 1 to: samples size by: sineTable size do:
> > [:i| samples replaceFrom: i to: (i + sineTable size - 1 min: 16000)
> with: sineTable startingAt: 1].
> > 1 to: 146 do: "smooth start and end of the sound"
> > [:i|
> > samples at: i put: ((samples at: i) * i / 146) asInteger.
> > samples at: 16001 - i put: ((samples at: 16001 - i) * i / 146)
> asInteger].
> > (SampledSound samples: samples samplingRate: 16000) play
> >
> > Now let's create a stereo sound image and try and play that:
> >
> > | samples sineTable sound |
> > "1 second of A below middle C (220Hz). 16000 / 220 is 72.72 recurring"
> > sineTable := SoundPlayer sineTable: 73.
> > sineTable doWithIndex:
> > [:sample :index| sineTable at: index put: sample // 4].
> > samples := SoundBuffer new: 16000.
> > 1 to: samples size by: sineTable size do:
> > [:i| samples replaceFrom: i to: (i + sineTable size - 1 min: 16000)
> with: sineTable startingAt: 1].
> > 1 to: 146 do:
> > [:i|
> > samples at: i put: ((samples at: i) * i / 146) asInteger.
> > samples at: 16001 - i put: ((samples at: 16001 - i) * i / 146)
> asInteger].
> > sound := SampledSound samples: samples samplingRate: 16000.
> > sound := MixedSound new
> > add: sound pan: 0.25;
> > add: sound pan: 0.75;
>
> If you replace the above line with
>
> > add: sound copy pan: 0.75;
>
> then the produced sound should be okay. Sound objects have state, and if
> you pass the same object twice, the state will be messed up.
>

Thank you!  This has cost me a day.  I'd say that it fails the principle of
least astonishment.  I'm going to see if I can add a check to add:pan: or
the mixdown step that would warn of this requirement.

Levente
>
> > yourself.
> > sound play
> >
> > Eek!!
> >
> > You can examine the mixing without hurting your ears by replacing
> >     "sound play"
> > with
> >     "sound computeSamplesForSeconds: sound duration"
> > which invokes the mixing directly.
> >
> > Any help making sense of this gratefully received.  Some comments around
> the
> >
> > scaledIndex := scaledIndex + scaledIncrement.
> > scaledIndex >= ScaledIndexOverflow ifTrue: [
> > overflow := scaledIndex >> IncrementFractionBits.
> > indexHighBits := indexHighBits + overflow.
> > scaledIndex := scaledIndex - (overflow << IncrementFractionBits)].
> >
> > in SampledSound>>#mixSampleCount:into:startingAt:leftVol:rightVol: would
> be most welcome.
> >
> > And if you simply comment out the primitive teh Smaklltalk code produces
> garbage also, so the problem does not seem to be Slang but the algorithm
> itself.
> >
> > _,,,^..^,,,_
> > best, Eliot
> >
> >
>


-- 
_,,,^..^,,,_
best, Eliot
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