Well nothing to do with sound ever seems as simple as one would like. 

Remember, the waggling keyboard thing makes horrific scratchy noises BUT it doesn't do that on a Mac running exactly the same Smalltalk code, so I got suspicious.

I now have three Pi setups that make completely different sounds.

1) an old Pi-top CEED with a Pi 3 and a May 2017 OS, 
a)with the as-provided NuScratch. This makes perfectly ok sounds under the piano-waggle regime, event though the volume is 100%. 
b) same Pi-top but using a newer (but still 2017 vintage) Squeak system, where the sound seems fine.
Both cases are using the old release of alsa.

2) my main daily use Pi4 with the last non-pulse version of OS. 
a) using the supplied NuScratch it makes barely audible noises that are terrible when actually audible. Even the cat meow is terrible!
b) using an early-this-year Squeak VM there is just no sound at all

3) a fresh Pi4 with the release candidate OS Simon pointed me to.
a) in as-supplied NuScratch with a pulse audio sound lib added the sound is bad unless the internal volume is turned way down, when there are still nasty scratchy-glitches
b) in a new system the sound is still bad but much nearer to ok with the internal volume reduced.

As mentioned, the Mac runs the exact same Smalltalk image just fine. I don't have Windows so I can't  opine on that option. Other than "Eww, Windows?"

The obvious thing to dig into now is what changes have been made to the lowest-level unix sound stuff since 2016. Anybody got ideas? Could it even be changes to the unix libraries in the pulse/alsa world?

tim
--
tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
Strange OpCodes: MET: Misread and Eat Tape