When Spi runs on a RPi …
How much of the memory ( SD ) is used ?
The reason I ask …
I switched to USB boot … And it seemed to
hamper the sound … Sort of hollow , plus
static on pieces that were fine with the SD …
This was on a 3B+ so type 2 USB …
Seems OK with 4B ( type 3 )
Of course it could be my imagination …
@hitsware - I cannot say for certain whether it is this particular issue or not, but here is something that may be relevant:
The article talks about a setting that can be changed to stop a Pi constantly polling for the presence of an SD card, which may help you.
@ethancrawford
Thank You …
So … During playing a synth piece …
Does data go back and forth to memory
( SD or USB ) ?
ALSO !
Has there been any changes to the code …
( RPi repository to .deb ) that would change
the sound ? … The ’ piano ’ synth seems different ?
Maybe my Wife hit me in the head with a baseball
bat while I slept ?
As far as the :piano synth, it was modified a little while ago:
! FWIW !
AND
I find it gratifying … 
( .deb version on RPi 4 ( usb boot ) )
Pulled out the usb stick while playing a piece .
The screen disappeared , BUT , the music
played on without a hitch !