Disable the automatic stereo-forcing heuristic for multichannel ALSA ... - #558
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Disable the automatic stereo-forcing heuristic for multichannel ALSA ...#558diamondsea11 wants to merge 1 commit into
diamondsea11 wants to merge 1 commit into
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…devices ShouldForceStereoChannels() collapses a device to stereo based on inspecting its ALSA channel map -- the function's own comment already describes it as "high-risk code, because it attempts to anticipate hypothetical device configurations with no actual testing." On genuinely multichannel interfaces (more than 2 real channels, not a legacy device reporting a bogus channel count) this heuristic misfires and forces the device down to 2 channels it does not actually need collapsing. This disables the heuristic unconditionally for channelsMax > 2, rather than attempting to refine it. The original channel-map-inspection logic is left in place below the new early return -- intentionally not deleted, so the exact conditions it was trying to detect remain visible for whoever decides its long-term fate. The channelsMax <= 2 fast path above is untouched. Test status, stated plainly rather than implied: there is no isolated unit test for this function, and writing one that means anything would need either real device channel-map fixtures or refactoring the function to take mock channel-map data instead of live snd_pcm_t/hw_params handles. Flagging this rather than claiming coverage that does not exist. Extracted as a single, minimal change from the diamondsea11/pipedal fork (feature/multipath-v1) for independent review, per the maintainer's request in rerdavies#555 to evaluate fork changes one topic at a time rather than as one combined diff. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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All four extracted branches are now open as drafts against rerdavies/pipedal: rerdavies#558 ALSA multichannel, rerdavies#559 S24_LE scaling, rerdavies#560 JUCE sidechain group fallback, rerdavies#561 LV2 category patching. All target main, which is what the branches were cut from; retargeting to dev is offered in each PR body. rerdavies#558 already existed as a non-draft and was converted, with its auto-populated commit-message body replaced by one written for review. Each PR body states the provenance Robin asked about in rerdavies#555 (not a developer, AI-implemented from descriptions) so he can calibrate review effort, and states verification honestly per PR -- only rerdavies#561 has actually been compiled. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Extracted from the
diamondsea11/pipedalfork as one self-contained change, per your request in #555 to review fork work one topic at a time rather than as a single large diff.What this does
ShouldForceStereoChannels()inspects a device's ALSA channel map and collapses it to stereo when the map looks like a legacy or surround configuration. On genuinely multichannel interfaces (more than 2 real channels, not a legacy driver reporting a bogus count) that heuristic misfires and forces the device down to 2 channels it does not need collapsing to.This adds an unconditional early return for
channelsMax > 2, disabling the heuristic rather than trying to refine it.Diff is one line. The original channel-map logic is deliberately left in place below the new return, not deleted, so the conditions it was trying to detect stay visible for whoever decides its long-term fate. The
channelsMax <= 2fast path above is untouched.Your own comment on that function already reads:
so this may be a change you'd rather make differently — happy to follow your lead on that.
Test status
There is no isolated unit test for this function, and I have not added one. Writing a meaningful test needs either real device channel-map fixtures or refactoring the function to accept mock channel-map data instead of live
snd_pcm_t/hw_paramshandles. Flagging that rather than implying coverage that doesn't exist.Verified in practice only on the hardware I have here (RME Babyface Pro FS, 4 in / 4 out), where the heuristic was the thing preventing all four channels from being available.
Provenance
As discussed in #555: I'm not a developer, and this code is AI-implemented from my descriptions. Please review it as such. I've kept the change as small as I could specifically so that reviewing it is cheap.
Targeting
mainsince that's what the branch is based on — happy to retarget todevif you'd prefer.