** Description changed: When using an S/PDIF output connected to an external Dolby Digital decoder (Logitech Z906), Ubuntu's GNOME Sound Settings selects the S/PDIF device correctly but automatically changes the PipeWire audio profile from IEC958 AC3 5.1 passthrough to IEC958 stereo. This causes the external decoder to receive only stereo PCM instead of Dolby Digital 5.1. The correct 5.1 profile is available and works when selected manually through pavucontrol or pactl, but GNOME Sound Settings immediately overrides it. System Information Ubuntu version: Ubuntu 24.04 LTS Audio system: PipeWire with PulseAudio compatibility layer Session manager: WirePlumber 0.4.x Hardware: ASUS PRIME B450M-A motherboard AMD Family 17h/19h HD Audio Controller Realtek ALC887-VD codec S/PDIF output via motherboard S/PDIF bracket Logitech Z906 speaker system (Dolby Digital decoder) Hardware path Realtek ALC887-VD - | - | + | + | S/PDIF IEC958 output - | - | + | + | Logitech Z906 Dolby Digital decoder The hardware supports Dolby Digital 5.1 passthrough. Current behavior The card exposes these profiles: output:iec958-stereo output:iec958-ac3-surround-51 The AC3 profile works correctly. Running: pactl set-card-profile alsa_card.pci-0000_08_00.6 output:iec958-ac3-surround-51 results in: alsa_output.pci-0000_08_00.6.iec958-ac3-surround-51 with: Sample Specification: s32le 6ch 48000Hz The Logitech Z906 immediately detects and decodes 5.1 Dolby Digital correctly. However: Open Ubuntu Settings → Sound Select "Digital Output (S/PDIF)" The system changes the profile back to: output:iec958-stereo - Result: Sample Specification: s32le 2ch 48000Hz The Z906 receives stereo only. - Expected behavior: When selecting an S/PDIF output device, Ubuntu should preserve the user's selected profile. If the user previously selected: Digital Surround 5.1 (IEC958/AC3) Output then selecting that output device again should not silently change it to: Digital Stereo (IEC958) Output The profile should either: Be restored automatically, or Be exposed clearly in GNOME Sound Settings as a selectable option. Why this matters S/PDIF is different from normal analog output. For analog output: The PC performs channel separation. A 5.1 sink outputs six analog channels. For S/PDIF: The PC may need to send a compressed Dolby Digital/DTS stream. The external receiver performs decoding. A user with an external decoder expects: Stereo content → stereo Dolby Digital 5.1 content → 5.1 but currently Ubuntu forces the device into a stereo PCM profile unless advanced tools are used. - Workaround: The only working method is manually selecting: - output:iec958-ac3-surround-51 - using: - - pactl set-card-profile - - or pavucontrol. + using: pactl set-card-profile or pavucontrol. This is not reasonable for a normal desktop user. - Additional observation: GNOME Sound Settings appears to override PipeWire/WirePlumber's profile state instead of simply changing the active sink. The profile change can be observed with: pactl list cards | grep "Active Profile" Before selecting S/PDIF: Active Profile: output:iec958-ac3-surround-51 After selecting S/PDIF in GNOME Settings: Active Profile: output:iec958-stereo - Suggested fix Possible solutions: Make GNOME Sound Settings remember the last selected profile per device. Expose IEC958 AC3 passthrough profiles in the normal Sound settings UI. Do not automatically downgrade an explicitly selected passthrough profile to stereo. Allow WirePlumber's restored profile preference to take priority over GNOME's device selection logic. - - Severity: + Severity: Medium. The hardware works and the feature exists, but the default desktop UI prevents normal users from using supported hardware capabilities without command-line tools. - - ProblemType: Bug - DistroRelease: Ubuntu 24.04 - Package: alsa-base 1.0.25+dfsg-0ubuntu7 - ProcVersionSignature: Ubuntu 7.0.0-28.28~24.04.1-generic 7.0.12 - Uname: Linux 7.0.0-28-generic x86_64 - ApportVersion: 2.28.2-0ubuntu0.1 - Architecture: amd64 - AudioDevicesInUse: - USER PID ACCESS COMMAND - /dev/snd/controlC1: roger 3176 F.... wireplumber - /dev/snd/controlC0: roger 3176 F.... wireplumber - /dev/snd/seq: roger 3171 F.... pipewire - CasperMD5CheckResult: pass - CurrentDesktop: ubuntu:GNOME - Date: Thu Jul 23 12:40:39 2026 - InstallationDate: Installed on 2024-11-03 (627 days ago) - InstallationMedia: Ubuntu 24.04.1 LTS "Noble Numbat" - Release amd64 (20240827.1) - MachineType: Acer Swift SF315-41 - PackageArchitecture: all - SourcePackage: alsa-driver - Symptom: audio - UpgradeStatus: No upgrade log present (probably fresh install) - dmi.bios.date: 10/25/2018 - dmi.bios.release: 2.12 - dmi.bios.vendor: Insyde Corp. - dmi.bios.version: V2.12 - dmi.board.asset.tag: Type2 - Board Asset Tag - dmi.board.name: Becks_RR - dmi.board.vendor: RR - dmi.board.version: V2.12 - dmi.chassis.type: 10 - dmi.chassis.vendor: Acer - dmi.chassis.version: Chassis Version - dmi.ec.firmware.release: 1.4 - dmi.modalias: dmi:bvnInsydeCorp.:bvrV2.12:bd10/25/2018:br2.12:efr1.4:svnAcer:pnSwiftSF315-41:pvrV2.12:rvnRR:rnBecks_RR:rvrV2.12:cvnAcer:ct10:cvrChassisVersion:sku0000000000000000:pfaSwift3: - dmi.product.family: Swift 3 - dmi.product.name: Swift SF315-41 - dmi.product.sku: 0000000000000000 - dmi.product.version: V2.12 - dmi.sys.vendor: Acer
** Attachment removed: "AlsaInfo.txt" https://bugs.launchpad.net/ubuntu/+bug/2161617/+attachment/5985739/+files/AlsaInfo.txt ** Attachment removed: "CurrentDmesg.txt" https://bugs.launchpad.net/ubuntu/+bug/2161617/+attachment/5985740/+files/CurrentDmesg.txt ** Attachment removed: "Dependencies.txt" https://bugs.launchpad.net/ubuntu/+bug/2161617/+attachment/5985741/+files/Dependencies.txt ** Attachment removed: "ProcCpuinfoMinimal.txt" https://bugs.launchpad.net/ubuntu/+bug/2161617/+attachment/5985742/+files/ProcCpuinfoMinimal.txt ** Attachment removed: "ProcEnviron.txt" https://bugs.launchpad.net/ubuntu/+bug/2161617/+attachment/5985743/+files/ProcEnviron.txt ** Description changed: When using an S/PDIF output connected to an external Dolby Digital decoder (Logitech Z906), Ubuntu's GNOME Sound Settings selects the S/PDIF device correctly but automatically changes the PipeWire audio profile from IEC958 AC3 5.1 passthrough to IEC958 stereo. This causes the external decoder to receive only stereo PCM instead of Dolby Digital 5.1. The correct 5.1 profile is available and works when selected manually through pavucontrol or pactl, but GNOME Sound Settings immediately overrides it. System Information Ubuntu version: Ubuntu 24.04 LTS Audio system: PipeWire with PulseAudio compatibility layer Session manager: WirePlumber 0.4.x Hardware: ASUS PRIME B450M-A motherboard AMD Family 17h/19h HD Audio Controller Realtek ALC887-VD codec S/PDIF output via motherboard S/PDIF bracket Logitech Z906 speaker system (Dolby Digital decoder) Hardware path Realtek ALC887-VD | | S/PDIF IEC958 output | | Logitech Z906 Dolby Digital decoder The hardware supports Dolby Digital 5.1 passthrough. - Current behavior + + Current behavior: The card exposes these profiles: output:iec958-stereo output:iec958-ac3-surround-51 The AC3 profile works correctly. Running: - - pactl set-card-profile alsa_card.pci-0000_08_00.6 - output:iec958-ac3-surround-51 - + pactl set-card-profile alsa_card.pci-0000_08_00.6 output:iec958-ac3-surround-51 results in: - alsa_output.pci-0000_08_00.6.iec958-ac3-surround-51 - with: - Sample Specification: s32le 6ch 48000Hz The Logitech Z906 immediately detects and decodes 5.1 Dolby Digital correctly. However: Open Ubuntu Settings → Sound Select "Digital Output (S/PDIF)" The system changes the profile back to: output:iec958-stereo + Result: Sample Specification: s32le 2ch 48000Hz + The Z906 receives stereo only. - The Z906 receives stereo only. Expected behavior: When selecting an S/PDIF output device, Ubuntu should preserve the user's selected profile. - If the user previously selected: - - Digital Surround 5.1 (IEC958/AC3) Output - - then selecting that output device again should not silently change it - to: - - Digital Stereo (IEC958) Output + If the user previously selected: Digital Surround 5.1 (IEC958/AC3) Output + then selecting that output device again should not silently change it to: Digital Stereo (IEC958) Output The profile should either: Be restored automatically, or Be exposed clearly in GNOME Sound Settings as a selectable option. Why this matters S/PDIF is different from normal analog output. For analog output: The PC performs channel separation. A 5.1 sink outputs six analog channels. For S/PDIF: The PC may need to send a compressed Dolby Digital/DTS stream. The external receiver performs decoding. A user with an external decoder expects: Stereo content → stereo Dolby Digital 5.1 content → 5.1 but currently Ubuntu forces the device into a stereo PCM profile unless advanced tools are used. + Workaround: The only working method is manually selecting: output:iec958-ac3-surround-51 using: pactl set-card-profile or pavucontrol. This is not reasonable for a normal desktop user. Additional observation: GNOME Sound Settings appears to override PipeWire/WirePlumber's profile state instead of simply changing the active sink. The profile change can be observed with: pactl list cards | grep "Active Profile" Before selecting S/PDIF: Active Profile: output:iec958-ac3-surround-51 After selecting S/PDIF in GNOME Settings: Active Profile: output:iec958-stereo - Possible solutions: Make GNOME Sound Settings remember the last selected profile per device. Expose IEC958 AC3 passthrough profiles in the normal Sound settings UI. Do not automatically downgrade an explicitly selected passthrough profile to stereo. Allow WirePlumber's restored profile preference to take priority over GNOME's device selection logic. Severity: Medium. The hardware works and the feature exists, but the default desktop UI prevents normal users from using supported hardware capabilities without command-line tools. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/2161617 Title: Selecting S/PDIF Digital Output in GNOME Sound Settings automatically switches IEC958 AC3 5.1 profile back to stereo To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+bug/2161617/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
