From 34215fbd32054e101a1add65bb888df531a5a18f Mon Sep 17 00:00:00 2001
From: OmikronApex <r.kasparek@web.de>
Date: Sun, 12 Jul 2026 01:46:03 +0200
Subject: [PATCH] fix(static): request raw stereo audio for the loopback
 capture track
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Chromium treats a getDisplayMedia audio track as a voice call by
default: echo cancellation, noise suppression, auto gain control and
mono downmix. Music through that pipeline is the tester-reported
"tin can" sound on ASIO/exclusive outputs.

Request the raw path explicitly (EC/NS/AGC off, stereo, 48 kHz) —
all constraints are best-effort so unsupported ones degrade silently
instead of failing the capture. The [asio-diag] loopback line now
dumps track.getSettings() so logs prove which processing actually
applied.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
---
 static/js/juce-audio.js | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/static/js/juce-audio.js b/static/js/juce-audio.js
index 8122089..bf279a3 100644
--- a/static/js/juce-audio.js
+++ b/static/js/juce-audio.js
@@ -614,9 +614,22 @@ import { S } from './player-state.js';
     let _lbStream = null, _lbCtx = null, _lbTap = null, _lbPageMuted = false;
     let _loopbackUnavailable = false;   // sticky: probe once, then fall back
     async function _engageLoopback() {
+        // Chromium's default capture pipeline treats the audio track as a
+        // VOICE call: echo cancellation + noise suppression + AGC + mono
+        // downmix. On music that is the "tin can" sound (tester 2026-07-12).
+        // Request the raw stereo path explicitly — every constraint here is
+        // best-effort (ideal-valued), so unsupported ones degrade silently
+        // rather than failing the capture.
         const stream = await navigator.mediaDevices.getDisplayMedia({
             video: true,
-            audio: { suppressLocalAudioPlayback: true },
+            audio: {
+                suppressLocalAudioPlayback: true,
+                echoCancellation: false,
+                noiseSuppression: false,
+                autoGainControl: false,
+                channelCount: 2,
+                sampleRate: 48000,
+            },
         });
         for (const t of stream.getVideoTracks()) t.stop();   // required, unused
         const track = stream.getAudioTracks()[0];
@@ -637,8 +650,19 @@ import { S } from './player-state.js';
                 _lbPageMuted = (await api.setPageMuted(true)) === true;
             }
             if (window._asioDiagEnabled?.()) {
+                // Full track settings: shows whether the raw-audio constraints
+                // (no EC/NS/AGC, stereo) actually took — a track that still
+                // reports echoCancellation=true or channelCount=1 explains
+                // "tin can" quality reports directly from the log.
+                const s = track.getSettings?.() || {};
                 console.log('[asio-diag] loopback: suppressed=', suppressed,
-                    'pageMuted=', _lbPageMuted, 'rate=', _lbCtx.sampleRate);
+                    'pageMuted=', _lbPageMuted, 'rate=', _lbCtx.sampleRate,
+                    'track=', JSON.stringify({
+                        sampleRate: s.sampleRate, channelCount: s.channelCount,
+                        echoCancellation: s.echoCancellation,
+                        noiseSuppression: s.noiseSuppression,
+                        autoGainControl: s.autoGainControl,
+                    }));
             }
             await api.setRendererBus(true, 1.0);
             tap.active = true;