Hi Stef,

On Sat, Sep 19, 2020 at 1:17 AM Stéphane Rollandin <lecteur at zogotounga.net>
wrote:

> >      if you play the example you’ll see that the first version works
> fine.  The second version, which adds MixedSound yo create stereo doesn’t.
> That proves that the issue is in MixedSound.  Please just try the two
> examples.
>
> Right. What I can see If I do
>
> | 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;
>                         yourself.
> (SampledSound samples: sound monoSamples samplingRate: sound
> originalSamplingRate) edit
>
> in the muO image I pointed to in my previous message, is a phasing
> problem leading to periodic glitches (the attached image is directly
> taken from the muO editor)
>

[image: image.png]

Interesting!!  I don't see this in my data, but I do see evidence of an
off-by-one error in misdown.  Here's the start, first zero crossing, and
end of the mono sound (the original samples sound buffer)

 { samples first: 8. samples copyFrom: 70 to: 77. samples last: 8 }
{a SoundBuffer(4 19 42 75 117 166 222 285) .
 a SoundBuffer(-1003 -682 -347 0 356 720 1088 1457) .
 a SoundBuffer(221 222 213 196 170 136 96 50)}

So these look fine and smooth.

But here's the corresponding data from the computeSamplesForSeconds: result
of the MixedSound:
{ self first: 16. self copyFrom: 70 * 2 to: 77 * 2 + 1. self last: 16 }
 {a SoundBuffer(4 4 4 4 18 18 41 41 41 41 74 74 116 116 165 165) .
  a SoundBuffer(-2712 -2712 -2712 -2836 -2836 -2940 -2940 -2940 -2940 -3022
-3022 -3084 -3084 -3124 -3124 -3214) .
  a SoundBuffer(212 212 212 212 196 196 169 169 169 169 136 136 96 96 49
49)}

The data *should* start with a SoundBuffer(4 4 18 18...
The data ends well.  But the first crossing is completely wrong.

Strange, because it sounds ok...

Let me count the crossings using:
| sign crossings |
crossings := 0.
sign := self first sign.
self do:
[:each|
each sign = sign negated ifTrue:
[crossings := crossings + 1.
sign := each sign]].
crossings

Both give 438 as expected.  Strange.  Why is there no crossing between 140
and 154 in the mixed down sound?


Ah, ok, the sample rate has changed:


| sign crossings ncrossings |
ncrossings := 0.
crossings := OrderedCollection new.
sign := self first sign.
self doWithIndex:
[:each :idx|
each sign = sign negated ifTrue:
[crossings add: idx - 1 -> idx.
ncrossings := ncrossings + 1.
sign := each sign]].
{ crossings first: 4. ncrossings } {an OrderedCollection(100->101 202->203
302->303 404->405) . 438}


So everything is fine *except for* the extra sample at the beginning.
That's clearly an error, right?

I'm looking at this..
>
> Stef
>

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