To give hope to others in a similar mess, I have hopefully SOLVED my no-sound problem by scouring several threads on the same subject,and removing pulseaudio
For good measure, in VLC
according to other advice, I went to Tools-Preferences-Audio and asked specifically for ALSA and the exact audio device (rather than 'default') from its drop-down list. This dialogue has two views, Simple/All; be sure to look at both
and all scroll-hidden options.
Since other Linux distributions seem to cope with no hassle, this seems to be alas the Achilles Heel of LinuxMint - at least the Debian flavour. There are many postings on the subject, and some of the suggested remedies are very technical. This one was the easiest. I was about to praise up this LinuxMint Debian/XFCE distribution as the best I have met for years; but this issue has dampened my entheusiasm. Since it is a well-know weakness, why cannot LinuxMint do at least as well as others in this field? All-round, they do better!
Best of luck Lewis Smith