[squeak-dev] Sound mixing makes nasty noises

David T. Lewis lewis at mail.msen.com
Sat Dec 26 19:48:00 UTC 2020

On Fri, Dec 25, 2020 at 11:32:52AM -0800, tim Rowledge wrote:
>> On 2020-12-25, at 6:03 AM, Herbert K??nig <herbertkoenig at gmx.net> wrote:
>> Am 25.12.2020 um 14:54 schrieb K K Subbu:
>>> On 25/12/20 6:49 pm, Herbert K??nig wrote:
>>>> It would be cool if someone can implement Your suggestion on how to
>>>> write Squeak's audio output buffers to a file because then I could
>>>> discern if the whole mess gets created by Squeak or if the OS plays a
>>>> role too.
>>> You may use parec (sound capture to file) and paplay (file to sound
>>> output) to test the audio subsystem of the OS to rule out any audio
>>> driver or mixer configuration problems [1]. The corresponding ALSA
>>> utilities are arecord and aplay. The mixer is alsamixer.
>>> padsp acts as a relay between the older /dev/dsp (audio device under
>>> OSS) and the newer /dev/snd/* (audio i/o devices).
>>> [1] https://manpages.debian.org/testing/pulseaudio-utils/pacat.1.en.html
>>> HTH .. Subbu
>> Hey you seem to know Linux's audio stuff.
>> Thanks!
>> Herbert
> I'm glad a few people around here do - there seems to be a bewildering
> mix of things out there.
> Looking at the assorted C code for soundplugin, sqUnixSound, sqUnixSoundALSA
> & SsqUnixSoundPulseAudio I see a bunch of places where pointer types
> don't agree and just maybe there are some problems there. The worst potential
> for pointer issues is avoided in practice because we never actually pass any
> value for startIndex other than 0 (the '1' used in all the Smalltalk is
> pre-decremented in SoundPlugin>primitiveSoundPlaySamples)
> Both the ALSA & pulseaudio files appear to connect to the semaphore in a
> reasonable manner. Ther pulseaudio code is clearly long untouched and in
> need of a lot of tidying up and the addition of a number of new routines
> like sound_GetDefaultSoundPlayer - try using that prim and it just dumps
> you VM with extreme prejudice!
> I think one of the really puzzling things right now is how does my older
> Pi setup *not* make such terrible noises? The scratch image & vm involved
> are *identical* to the ones on the newer-but-still-alsa Pi.

Tim, I adapted your earlier code example as follows:

	volume := 0.30.
	{ 55 . 60 . 64 }
		collect: [ :e |
			FMSound new
				setPitch: (AbstractSound pitchForMIDIKey: e)
				dur: 5
				loudness: volume]
		thenDo: [:s |  s play. (Delay forSeconds: 1) wait ].

This plays a major triad, which makes it very easy to hear the clipping
distortion. On my Linux PC with pulse audio, I get audible clipping
distortion when volume in the snippet above is set to anything higher
than 0.30. Results are very similar regardless of the VM and the image
version. I tried Squeak 3.8, Squeak trunk, interpreter VM, Spur64 VM,
and SqueakJS on Chrome.

Maybe you can compare this on Raspbery Pi and see if you get the same


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