Lock-to-clock always on (remove option); service audio hardcoded to Opus live config

Ed, 2026-07-17. The bigger half of the service crackle fix: raw PCM sounded hideous;
Opus at the live-jamming frame with Small packets and lock-to-clock sounds right.

Lock to audio clock (TightLatencyMode) is now ALWAYS ON and no longer a user option:
- Removed the checkbox from the main window and the service dialog. Nobody ever runs
  with it off -- off just adds delay.
- Main app forces the sender tight at startup; Profile.TightLatencyMode defaults true
  and is kept only for file compatibility. Load/SaveTightLatencyMode accessors removed.

Service audio profile is now fixed and unconfigurable:
- Removed the "Audio profile" tab from the service config dialog entirely (two tabs
  left: Connectivity, Audio send).
- The service FORCES Opus + 2.5 ms frame (120 samples) + Small packets + lock-to-clock
  at runtime in ServiceSendHost.ApplyProfile, ignoring whatever the profile carries, so
  a stale/hand-edited profile can never put it back on a bad codec. SaveToProfile writes
  the same fixed values.

Robustness: ApplyProfile now swallows a capture Start() failure (with lock-to-clock
always on the WASAPI lane is push-mode, which opens the device synchronously and throws
if it is invalid/gone) -- presence stays up and the device-watcher/self-heal re-open when
a device is available, instead of the exception crashing the service loop.

Self-test "Service sender parity" rewritten to prove the service overrides a PCM profile
to Opus/120. Gate: 39/39.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/RemSound.App/MainForm.cs

@@ -289,7 +289,6 @@ public sealed class MainForm : Form
     private readonly AccessibleCheckBox continuousTuneAsioBox = new() { Text = "Continuous auto-tune ASIO latency", AutoSize = true };
     private readonly ListBox smoothnessBox = new() { Width = 420, Height = 200, IntegralHeight = false, AccessibleName = "Buffer smoothness (Alt+B)" };
     private readonly ListBox artefactBox = new() { Width = 420, Height = 60, IntegralHeight = false, AccessibleName = "Artefact sound type (Alt+A) — controls how audio gaps sound" };
-    private readonly AccessibleCheckBox tightLatencyBox = new() { AutoSize = true };
     // Priority mode (per profile). Sits as the first control on the Audio profile tab,
     // ungrouped above the two GroupBoxes, so it's the first thing focus lands on when the
     // user Tabs into the tab. Toggling marks the profile dirty (the setting lives in
@@ -1122,12 +1121,10 @@ public sealed class MainForm : Form
         // The receiver-side hook was removed in the 2026-05-06 cleanup since the resampler is
         // no longer in the receive path. The dialog checkbox label still says "Lock to audio
         // clock" but only affects the sender now.
-        var initialTightLatency = settings.LoadTightLatencyMode();
-        sender.SetTightLatency(initialTightLatency);
-        // Log it so post-test analysis can correlate clicks with tight-latency state without
-        // having to infer from sender-engine restarts. Includes the audio mode because what
-        // "tight" means is mode-dependent (per-callback ASIO emission vs. WASAPI push-mode).
-        logFile.Event($"tight latency at startup: {(initialTightLatency ? "on" : "off")} (audio mode={settings.LoadAudioMode()})");
+        // Lock to audio clock is always on now (no longer a user option) — put the sender into
+        // tight-latency mode unconditionally.
+        sender.SetTightLatency(true);
+        logFile.Event($"tight latency at startup: on (always) (audio mode={settings.LoadAudioMode()})");
 
         // Priority mode (per-profile). Applies every PerformanceMode lever on first launch
         // under this profile so the OS doesn't start coasting before the user has tabbed
@@ -4630,40 +4627,10 @@ public sealed class MainForm : Form
         panel.Controls.Add(codecAndSendLabel, 0, 0);
         panel.Controls.Add(codecRowPanel, 1, 0);
 
-        // === Row 1: Tight latency (sender-side, mode-dependent label) ===
-        // Mnemonic was Alt+K until v1.5 (2026-05-15) when the Record menu took Alt+K at
-        // the menu-bar level. Replaced with Alt+D — the D in "au&dio" is naturally part of
-        // the word, no explicit "(Alt+...)" hint needed. Free on the Audio profile tab
-        // (no other Audio-profile control uses D).
-        var currentAudioModeForLabel = settings.LoadAudioMode();
-        var tightLatencyText = currentAudioModeForLabel switch
-        {
-            AudioMode.WasapiOnly      => "Lock to au&dio clock, WASAPI sender",
-            AudioMode.BothIndependent => "Lock to au&dio clock, WASAPI + ASIO senders",
-            _                         => "Lock to au&dio clock",
-        };
-        var tightLatencyAccessible = currentAudioModeForLabel switch
-        {
-            AudioMode.WasapiOnly      => "Lock to audio clock (Alt+D) — sender uses the WASAPI capture event for timing instead of a Stopwatch tick. Tightens delay; brief clicks possible if the link can't keep up.",
-            AudioMode.BothIndependent => "Lock to audio clock (Alt+D) — both lanes tighten independently. WASAPI lane uses push-mode (single source); ASIO lane emits per callback. Brief clicks possible on either if the link can't keep up.",
-            _                         => "Lock to audio clock (Alt+D) — sender-side timing tighten.",
-        };
-        tightLatencyBox.Text = tightLatencyText;
-        tightLatencyBox.AccessibleName = tightLatencyAccessible;
-        tightLatencyBox.Checked = settings.LoadTightLatencyMode();
-        tightLatencyBox.CheckedChanged += (_, _) =>
-        {
-            settings.SaveTightLatencyMode(tightLatencyBox.Checked);
-            sender.SetTightLatency(tightLatencyBox.Checked);
-            logFile.Event($"tight latency changed to {(tightLatencyBox.Checked ? "on" : "off")} (audio mode={settings.LoadAudioMode()})");
-            MarkProfileDirty();
-        };
-        var tightLatencyLabel = new Label { Text = tightLatencyText, AutoSize = true, Anchor = AnchorStyles.Left };
-        tightLatencyLabel.Click += (_, _) => tightLatencyBox.Focus();
-        var tightLatencyContainer = new FlowLayoutPanel { AutoSize = true, Dock = DockStyle.Fill };
-        tightLatencyContainer.Controls.Add(tightLatencyBox);
-        panel.Controls.Add(tightLatencyLabel, 0, 1);
-        panel.Controls.Add(tightLatencyContainer, 1, 1);
+        // "Lock to audio clock" (sender uses the WASAPI capture event for timing instead of a Stopwatch
+        // tick) is now ALWAYS ON and is no longer a user option (Ed, 2026-07-17: nobody ever runs with it
+        // off — off just adds delay). The sender is put into tight-latency mode unconditionally at startup;
+        // the old per-profile checkbox is gone.
 
         group.Controls.Add(panel);
     }
@@ -9493,8 +9460,8 @@ public sealed class MainForm : Form
             // EffectiveOpusFrameSamples is samples-per-channel at 48 kHz; ÷ 48 → ms, ÷ 2 → half-frame.
             return EffectiveOpusFrameSamples(item.Codec, item.OpusFrameSamples, rate) / 96.0;
         }
-        // PCM
-        if (settings.LoadTightLatencyMode() && settings.LoadAudioMode() == AudioMode.AsioOnly)
+        // PCM. Lock to audio clock is always on now, so ASIO-only means per-callback emission.
+        if (settings.LoadAudioMode() == AudioMode.AsioOnly)
         {
             return 0.5; // per-callback ASIO send → ~one ASIO buffer, hard to know without driver introspection
         }

src/RemSound.App/SelfTest.cs

@@ -806,12 +806,15 @@ internal static class SelfTest
     /// divergences found auditing the service against the main app.</summary>
     private static string? ServiceSenderParity()
     {
+        // The profile deliberately carries the WRONG audio transport (raw PCM, broadcast frame, Standard
+        // rate) to prove the service IGNORES it and forces its known-good live config (Opus, 2.5 ms frame,
+        // Small packets, lock-to-clock) — the fix for the crackly-service report (Ed, 2026-07-17).
         var profile = new Profile
         {
             Title = "parity",
-            Codec = AudioTransportCodec.Opus,
-            OpusFrameSamplesPerChannel = 960,   // broadcast
-            SendRate = SendRate.Tight,          // "Small" — should halve the Opus frame to 480
+            Codec = AudioTransportCodec.Pcm,
+            OpusFrameSamplesPerChannel = 960,
+            SendRate = SendRate.Standard,
             WasapiSendMode = "devices",
         };
         profile.SelectedWasapiSendOutputs.Add("fake-device-id");     // a source so ApplyProfile proceeds
@@ -820,17 +823,20 @@ internal static class SelfTest
         profile.Password = RemSoundCrypto.Obfuscate(pw);
 
         using var host = new ServiceSendHost(() => profile);
-        Check(host.ApplyProfile(profile), "ApplyProfile should proceed with a source + peer + password");
+        // ApplyProfile sets the sender's crypto + codec BEFORE it opens the (fake) device; a device-open
+        // failure is now swallowed inside ApplyProfile, so this returns and the config is readable.
+        host.ApplyProfile(profile);
         var cfg = host.SenderConfigForTest;
 
         Check(cfg.Key is { Length: > 0 } && cfg.Key.SequenceEqual(RemSoundCrypto.DeriveKey(pw)),
             "the service must set the audio key = DeriveKey(password)");
         Check(cfg.Fingerprint is { Length: > 0 } && cfg.Fingerprint.SequenceEqual(RemSoundCrypto.Fingerprint(pw)),
             "the service must set the audio FINGERPRINT = Fingerprint(password), or the peer rejects the stream");
-        Check(cfg.Codec == AudioTransportCodec.Opus, "codec must round-trip to the sender");
-        Check(cfg.Frame == MainForm.EffectiveOpusFrameSamples(AudioTransportCodec.Opus, 960, SendRate.Tight) && cfg.Frame == 480,
-            $"the Small send rate must halve the Opus frame like the main app (got {cfg.Frame})");
-        return "key + fingerprint + effective Opus frame match the main app";
+        Check(cfg.Codec == AudioTransportCodec.Opus,
+            $"the service must FORCE Opus regardless of the profile codec (got {cfg.Codec})");
+        Check(cfg.Frame == 120,
+            $"the service must force the 2.5 ms live Opus frame (120 samples), regardless of the profile (got {cfg.Frame})");
+        return "service forces Opus + 2.5ms frame + lock-to-clock regardless of profile; crypto matches";
     }
 
     /// <summary>The lock-screen service's app-yield token: while a hold is active the service must see an

src/RemSound.App/ServiceProfileDialog.cs

@@ -7,8 +7,9 @@ namespace RemSound.App;
 /// The "Configure RemSound service profile" dialog: a self-contained, modal editor for the send-only
 /// service profile, built to match the main window — same house controls, same layout rows, and the
 /// same screen-reader wiring on the lists (via <see cref="CheckedListAccessibility"/>), so it reads and
-/// behaves exactly like the real tabs. Tab order mirrors the main window: Connectivity, then Audio send,
-/// then Audio profile. Send-only and WASAPI-only: no receive controls, no ASIO, no "Send my audio"
+/// behaves exactly like the real tabs. Two tabs: Connectivity, then Audio send. The Audio profile tab
+/// was removed (2026-07-17) — codec/packet/lock-to-clock are fixed to known-good live values so nobody
+/// mis-tunes the service. Send-only and WASAPI-only: no receive controls, no ASIO, no "Send my audio"
 /// toggle. Edits a <see cref="Profile"/> clone; nothing is persisted until the caller acts on OK.
 /// </summary>
 internal sealed class ServiceProfileDialog : Form
@@ -37,10 +38,13 @@ internal sealed class ServiceProfileDialog : Form
     private readonly Label inputsStatus = new() { AutoSize = true, Text = "No input device selected." };
     private MnemonicLabel? sendModeLabel, outputsLabel, appsLabel, inputsLabel;
 
-    // --- Audio profile tab ---
-    private readonly ComboBox codecBox = new() { DropDownStyle = ComboBoxStyle.DropDownList, Width = 360, AccessibleName = "Audio codec (Alt+C)" };
-    private readonly ListBox sendRateBox = new() { Width = 360, Height = 40, IntegralHeight = false, AccessibleName = "Packet size (Alt+P)" };
-    private readonly AccessibleCheckBox tightLatencyBox = new() { AutoSize = true };
+    // No "Audio profile" tab: the service always sends Opus at the live-jamming frame (2.5 ms), Small
+    // packets, and locked to the audio clock — the settings Ed found sound good. They're forced in
+    // SaveToProfile below and again at runtime in ServiceSendHost, so there's nothing to misconfigure
+    // (Ed, 2026-07-17: removed the tab; nobody should be touching these).
+    private const AudioTransportCodec ServiceCodec = AudioTransportCodec.Opus;
+    private const int ServiceOpusFrameSamples = 120;      // 2.5 ms at 48 kHz — live latency
+    private const SendRate ServiceSendRate = SendRate.Tight; // "Small" packets
 
     // --- Button row ---
     private readonly Button saveButton = new() { Text = "&Save and Close", AutoSize = true, DialogResult = DialogResult.OK };
@@ -69,10 +73,10 @@ internal sealed class ServiceProfileDialog : Form
         AccessibleName = "Configure RemSound service profile";
         if (Theme.AppIcon is { } icon) Icon = icon;
 
-        // Tabs in the main window's order: Connectivity, Audio send, Audio profile.
+        // Two tabs only now: Connectivity and Audio send. The Audio profile tab was removed — the codec,
+        // packet size and lock-to-clock are fixed to known-good live-jamming values (see fields above).
         BuildConnectivityTab();
         BuildAudioSendTab();
-        BuildAudioProfileTab();
         BuildButtonRow();
 
         LoadFromProfile();
@@ -168,33 +172,6 @@ internal sealed class ServiceProfileDialog : Form
         tabs.TabPages.Add(page);
     }
 
-    private void BuildAudioProfileTab()
-    {
-        var page = new TabPage("Audio profile");
-        var panel = NewPanel();
-
-        // Exact same codec choices, packet-size items and lock-to-clock label as the main window.
-        codecBox.Items.AddRange(new object[]
-        {
-            new CodecChoice("PCM 48K 24 bit — uncompressed", AudioTransportCodec.Pcm, 0),
-            new CodecChoice("Opus, broadcast quality — loss tolerant", AudioTransportCodec.Opus, 960),
-            new CodecChoice("Opus, live latency — for jamming and monitoring", AudioTransportCodec.Opus, 120),
-        });
-        sendRateBox.Items.Add("Standard (5 ms PCM, 10/20 ms Opus)");
-        sendRateBox.Items.Add("Small (2.5 ms PCM, 5/10 ms Opus, LAN only)");
-        tightLatencyBox.Text = "Lock to au&dio clock, WASAPI sender";
-        tightLatencyBox.AccessibleName = "Lock to audio clock (Alt+D) — sender uses the WASAPI capture event for timing instead of a Stopwatch tick. Tightens delay; brief clicks possible if the link can't keep up.";
-
-        FormLayoutRows.AddRow(panel, 0, "Audio &codec (Alt+C)", codecBox, c => c.Focus());
-        FormLayoutRows.AddRow(panel, 1, "&Packet size (Alt+P)", sendRateBox, c => c.Focus());
-        var tightWrap = new FlowLayoutPanel { AutoSize = true, Dock = DockStyle.Fill };
-        tightWrap.Controls.Add(tightLatencyBox);
-        panel.Controls.Add(tightWrap, 1, 2);
-
-        page.Controls.Add(panel);
-        tabs.TabPages.Add(page);
-    }
-
     private void BuildButtonRow()
     {
         var outer = new TableLayoutPanel { Dock = DockStyle.Fill, ColumnCount = 1, RowCount = 2 };
@@ -237,10 +214,6 @@ internal sealed class ServiceProfileDialog : Form
             sendAllAppsBox.Checked = working.SendAllApplications;
             PopulateAppsList();
 
-            SelectCodec();
-            sendRateBox.SelectedIndex = Math.Clamp((int)working.SendRate, 0, sendRateBox.Items.Count - 1);
-            tightLatencyBox.Checked = working.TightLatencyMode;
-
             peersList.Items.Clear();
             var allPeers = working.RememberedPeers.Concat(working.SelectedConnectedPeers)
                 .Where(p => !string.IsNullOrWhiteSpace(p)).Distinct(StringComparer.OrdinalIgnoreCase).ToList();
@@ -263,9 +236,12 @@ internal sealed class ServiceProfileDialog : Form
         working.SendAllApplications = sendAllAppsBox.Checked;
         working.SelectedSendApplications = appsList.CheckedItems.OfType<AppRow>().Select(a => a.ProcessName).Distinct().ToList();
 
-        if (codecBox.SelectedItem is CodecChoice c) { working.Codec = c.Codec; working.OpusFrameSamplesPerChannel = c.OpusFrameSamples; }
-        working.SendRate = (SendRate)Math.Max(0, sendRateBox.SelectedIndex);
-        working.TightLatencyMode = tightLatencyBox.Checked;
+        // Audio profile is fixed for the service (no tab): Opus live-jamming frame, Small packets, locked
+        // to the audio clock. These are also re-forced at runtime in ServiceSendHost.
+        working.Codec = ServiceCodec;
+        working.OpusFrameSamplesPerChannel = ServiceOpusFrameSamples;
+        working.SendRate = ServiceSendRate;
+        working.TightLatencyMode = true;
 
         // Ticked peers are the ones the service sends to; keep every listed peer as remembered.
         working.SelectedConnectedPeers = peersList.CheckedItems.OfType<string>().Distinct().ToList();
@@ -303,14 +279,6 @@ internal sealed class ServiceProfileDialog : Form
         }
     }
 
-    private void SelectCodec()
-    {
-        foreach (var item in codecBox.Items.OfType<CodecChoice>())
-            if (item.Codec == working.Codec && (working.Codec == AudioTransportCodec.Pcm || item.OpusFrameSamples == working.OpusFrameSamplesPerChannel))
-            { codecBox.SelectedItem = item; return; }
-        if (codecBox.Items.Count > 0) codecBox.SelectedIndex = 0;
-    }
-
     private void ApplySendModeVisibility()
     {
         var supported = ProcessLoopbackCapture.IsSupported;

src/RemSound.App/ServiceSendHost.cs

@@ -311,19 +311,30 @@ public sealed class ServiceSendHost : IDisposable
             var plainPassword = string.IsNullOrEmpty(profile.Password) ? "" : RemSoundCrypto.Deobfuscate(profile.Password);
             sender.AudioKey = string.IsNullOrEmpty(plainPassword) ? null : RemSoundCrypto.DeriveKey(plainPassword);
             sender.AudioFingerprint = string.IsNullOrEmpty(plainPassword) ? null : RemSoundCrypto.Fingerprint(plainPassword);
-            // Opus frame size follows the send rate the same way the main app does (the "Small" rate
-            // halves the Opus frame) — otherwise the service would encode at a different frame than the
-            // main app would for the identical profile.
-            sender.ConfigureCodec(profile.Codec, MainForm.EffectiveOpusFrameSamples(profile.Codec, profile.OpusFrameSamplesPerChannel, profile.SendRate));
-            sender.SetSendRate(profile.SendRate);
-            sender.SetTightLatency(profile.TightLatencyMode);
+            // The service's audio transport is FIXED to the known-good live-jamming config, regardless of
+            // what the profile carries (the config dialog no longer exposes these — Ed, 2026-07-17). Raw
+            // PCM sounded hideous over the service; Opus at the 2.5 ms live frame with Small packets and
+            // lock-to-clock is what sounds right. Forcing it here means a stale or hand-edited profile can
+            // never put the service back on a bad codec.
+            const AudioTransportCodec serviceCodec = AudioTransportCodec.Opus;
+            const int serviceOpusFrameSamples = 120; // 2.5 ms at 48 kHz
+            const SendRate serviceSendRate = SendRate.Tight; // "Small" packets
+            sender.ConfigureCodec(serviceCodec, MainForm.EffectiveOpusFrameSamples(serviceCodec, serviceOpusFrameSamples, serviceSendRate));
+            sender.SetSendRate(serviceSendRate);
+            sender.SetTightLatency(true); // lock to audio clock — always on
             // Arm the full set to begin with (nothing is known-dead yet); RefreshSendArming then prunes any
             // peer the heartbeat can't reach and re-arms it when it recovers.
             allEndpoints = endpoints.ToArray();
             armedSignature = null;
             sender.SetReceivers(endpoints);
             sender.Configure(specs);
-            sender.Start();
+            // A device-open failure at Start must NOT throw out of the service loop. With lock-to-clock
+            // always on, the WASAPI lane uses push-mode, which opens the endpoint synchronously and throws
+            // (e.g. ArgumentException) if the device id is invalid or the device has vanished. Swallow it:
+            // presence still comes up, and the device-change watcher / self-heal re-open the capture when a
+            // good device appears. Without this guard a disappeared device would crash the whole service.
+            try { sender.Start(); }
+            catch (Exception ex) { log?.Invoke($"service: capture start failed ({ex.GetType().Name}: {ex.Message}) — presence up; will re-open when a device is available"); }
             SwapMeterDevices(specs); // endpoint-meter readers for the deaf-capture detector
             // Instant self-heal trigger: session-created notification on the default render device.
             // Recreated per apply so it re-points at the current default after a device change.

src/RemSound.Core/Profile.cs

@@ -107,7 +107,11 @@ public sealed class Profile
     [JsonPropertyName("OpusFrameMilliseconds")]
     public int OpusFrameSamplesPerChannel { get; set; } = 480;
     public int SendRateRaw { get; set; } = (int)SendRate.Standard;
-    public bool TightLatencyMode { get; set; }
+    /// <summary>"Lock to audio clock" — sender uses the WASAPI capture event for timing. As of 2026-07-17
+    /// this is ALWAYS ON and no longer user-configurable (the app forces it true at startup and the
+    /// service forces it per stream); the field is kept only for profile-file backward compatibility.
+    /// Defaults true so any freshly created profile reflects the real behaviour.</summary>
+    public bool TightLatencyMode { get; set; } = true;
     /// <summary>True if this profile asks Windows to keep the RemSound process in
     /// high-priority mode while it's running — CPU scheduling, power management, memory
     /// priority, working-set lock, and MMCSS thread priority all elevated. Off by default;

src/RemSound.Core/RemSoundSettingsStore.cs

@@ -279,21 +279,9 @@ public sealed class RemSoundSettingsStore
         Save(s);
     }
 
-    /// <summary>Tight-latency mode toggle. Sender-side only as of 2026-05-06 (the receiver no
-    /// longer has a resampler to bypass). In WasapiOnly + single source mode the sender swaps
-    /// from the timer-driven MixingEngine to the audio-clock-locked PushModeWasapiBackend; in
-    /// AsioOnly + PCM mode the sender emits one packet per ASIO callback instead of accumulating
-    /// to the chosen frame size. Saves a few ms of send-side latency at the cost of brief
-    /// clicks if the link can't keep up. Off by default.</summary>
-    public bool LoadTightLatencyMode(bool defaultValue = false) =>
-        Try(() => Load()?.TightLatencyMode) ?? defaultValue;
-
-    public void SaveTightLatencyMode(bool value)
-    {
-        var s = Load() ?? new Settings();
-        s.TightLatencyMode = value;
-        Save(s);
-    }
+    // Tight-latency mode ("Lock to audio clock") is ALWAYS ON as of 2026-07-17 — no longer a user option,
+    // so the Load/Save accessors were removed. The app forces the sender tight at startup and the service
+    // per stream. The Settings cache still round-trips Profile.TightLatencyMode for file compatibility.
 
     /// <summary>Priority mode for the current profile. When true, the App's
     /// <c>PerformanceMode</c> helper drives every Win32 lever that elevates a process's