[Audio Playback] right channel attenuated after random length of time

[Andrew Scott]

After playing sound for a while (minutes, not seconds), the right channel will become attenuated.

Restoring balance can be done by unplugging the headphones (from the built-in sound card) or disconnecting the external DAC and reconnecting it.

Balance can be restored by altering balance in pavucontrol, but if you balance by increasing the right side volume, it introduces a lot of distortion.

Same behavior observed using both the internal sound device as well as the Sound Blaster USB sound device, so it's in the mixing software somewhere.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: alsa-base 1.0.25+dfsg-0ubuntu5
ProcVersionSignature: Ubuntu 5.4.0-47.51-generic 5.4.55
Uname: Linux 5.4.0-47-generic x86_64
NonfreeKernelModules: nvidia_modeset nvidia
ApportVersion: 2.20.11-0ubuntu27.8
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Thu Sep 17 14:33:43 2020
InstallationDate: Installed on 2020-07-10 (69 days ago)
InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
PackageArchitecture: all
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: alsa-driver
Symptom: audio
Symptom_Card: SoundBlaster MP3+ - Sound Blaster MP3+
Symptom_PulseAudioLog:
 Sep 15 15:45:31 vmhost01 dbus-daemon[1765]: [system] Activating via systemd: service name='org.freedesktop.RealtimeKit1' unit='rtkit-daemon.service' requested by ':1.29' (uid=125 pid=2024 comm="/usr/bin/pulseaudio --daemonize=no --log-target=jo" label="unconfined")
 Sep 15 15:45:32 vmhost01 pulseaudio[2024]: No UCM verb is valid for hw:0
 Sep 15 15:45:33 vmhost01 pulseaudio[2024]: No UCM verb is valid for hw:2
 Sep 15 15:45:34 vmhost01 dbus-daemon[1765]: [system] Activating via systemd: service name='org.bluez' unit='dbus-org.bluez.service' requested by ':1.45' (uid=125 pid=2024 comm="/usr/bin/pulseaudio --daemonize=no --log-target=jo" label="unconfined")
 Sep 15 19:01:54 vmhost01 dbus-daemon[1765]: [system] Activating via systemd: service name='org.bluez' unit='dbus-org.bluez.service' requested by ':1.114' (uid=1000 pid=4820 comm="/usr/bin/pulseaudio --daemonize=no --log-target=jo" label="unconfined")
Symptom_Type: Sound works for a while, then breaks
Title: [USB-Audio - Sound Blaster MP3+, playback] fails after a while
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/16/2019
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 2901
dmi.board.asset.tag: Default string
dmi.board.name: ROG STRIX B450-F GAMING
dmi.board.vendor: ASUSTeK COMPUTER INC.
dmi.board.version: Rev 1.xx
dmi.chassis.asset.tag: Default string
dmi.chassis.type: 3
dmi.chassis.vendor: Default string
dmi.chassis.version: Default string
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr2901:bd10/16/2019:svnSystemmanufacturer:pnSystemProductName:pvrSystemVersion:rvnASUSTeKCOMPUTERINC.:rnROGSTRIXB450-FGAMING:rvrRev1.xx:cvnDefaultstring:ct3:cvrDefaultstring:
dmi.product.family: To be filled by O.E.M.
dmi.product.name: System Product Name
dmi.product.sku: SKU
dmi.product.version: System Version
dmi.sys.vendor: System manufacturer