Thanks Robin, although you over-explained lots of stuff (and sometimes you
misunderstood me), the trick that made it work well in this particular PC
was:
/usr/bin/jackd -R -P 70 -T -d alsa -n 3 -r 48000 -p 128 -d
I always used qjackctl... I prefer the mouse to the keyboard, I'm just
trying to figure out what stuff in Qjackctl I configured different from that
console command.
(I already had done the rest of the stuff - the linux-rt kernel, etc, etc -
)