[LAU] Distorted sound

[David Sumbler]

I am running Qtractor and QJackCtl on a Raspberry Pi 3B+, with sound
output through the headphone jack.

When I play a wav file using 'aplay' it sounds fine, but if I load it
into a track in Qtractor, it is very distorted.  A female voice sounds
like basso profundo (although the speed is correct) and is very
distorted.  It looks to me as if this is probably because the output of
Qtractor is not being directed through jackd.

QJackCtl seems to show that jack is running OK and speaking nicely to
Alsa, but there is one oddity.  The Qtractor Connections window shows,
in the Audio tab, the expected Qtractor output connected to System. 
Normally I would expect the QJackCtl Connect window to show the same in
its Audio tab, but in fact it shows nothing at all - neither Qtractor
nor System.  (Yet it is showing the expected Midi Through and Qtractor
on both sides of the Midi tab, cross connected as expected.)

The Messages tab of QJackCtl shows that jackd is running, but it
doesn't report anything extra when Qtractor is started.  Yet on my
Ubuntu machines, QJackCtl knows automatically when I start Qtractor.

Any ideas why QJackCtl doesn't seem to know what's trying to connect
through it?

David