Sound has stopped working after today's update

I had an alert to do an update today from the software-updater so I went ahead as usual and did the update.

As a result I now find that I get now sound out of my speakers. This is true on this machine and on another machine that has the same Ubuntu version (but slightly different hardware & different speakers).

In the pavucontrol when music or video is playing I have checked that nothing is muted. And I used alsamixer to turn off any muting there. And in fact there is only one sound output device (my speakers) and the sound is being shown since the indicator that shows decibels shows continual movement.

So actually, I don't think this is a bug in pavucontrol but in the sound system generally, but the bug report tool only lets you specify an actual package.

$ lsb_release -rd
Description: Ubuntu 16.04.4 LTS
Release: 16.04
$ apt-cache policy pavucontrol
pavucontrol:
  Installed: 3.0-3build1
  Candidate: 3.0-3build1
  Version table:
 *** 3.0-3build1 500
        500 http://gb.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: pavucontrol 3.0-3build1
ProcVersionSignature: Ubuntu 4.4.0-121.145-generic 4.4.117
Uname: Linux 4.4.0-121-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.16
Architecture: amd64
CurrentDesktop: XFCE
Date: Wed Apr 25 20:13:27 2018
InstallationDate: Installed on 2015-11-05 (902 days ago)
InstallationMedia: Xubuntu 14.04.3 LTS "Trusty Tahr" - Beta amd64 (20150805)
ProcEnviron:
 LANGUAGE=en_GB:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: pavucontrol
UpgradeStatus: No upgrade log present (probably fresh install)