Pan/EQ: add a per-peer volume slider (before pan)

Ed's request — an individual level fader per peer, sitting just before the pan control on the
Pan and EQ tab. New PeerShaping.Volume (0..1, default 1.0 = 100% = transparent), always applied
(no master switch — unity does nothing). It folds into PeerDspChain's L/R gain alongside pan
(gainL = panL*vol, gainR = panR*vol), so it's another per-sample multiply, zero added latency,
and multiplies with the global volume (per-peer fader -> mix -> master). Slider is 0-100%,
saved per profile, announces "Volume: N percent". Shaped recording captures it; raw (bypass)
recording doesn't. Held for next release.

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

src/RemSound.App/MainForm.cs

@@ -157,6 +157,7 @@ public sealed class MainForm : Form
     private readonly AccessibleCheckBox enableEqForPeersBox = new() { Text = "Enable &EQ for peers (Alt+E)", AccessibleName = "Enable EQ for peers", AutoSize = true };
     private readonly AccessibleCheckBox enablePanForPeersBox = new() { Text = "Enable &pan for peers (Alt+P)", AccessibleName = "Enable pan for peers", AutoSize = true };
     private readonly ListBox panEqPeerList = new() { Width = 430, Height = 90, AccessibleName = "Peer to shape" };
+    private readonly TrackBar volumeSlider = new() { Minimum = 0, Maximum = 100, Value = 100, SmallChange = 1, LargeChange = 10, TickFrequency = 25, Width = 320 };
     private readonly TrackBar panSlider = new() { Minimum = 0, Maximum = 100, Value = 50, SmallChange = 1, LargeChange = 10, TickFrequency = 25, Width = 320 };
     private readonly Button resetPeerEqButton = new() { Text = "Set peer E&Q to default (Alt+Q)", AutoSize = true, AccessibleName = "Set peer EQ to default" };
     private readonly ListBox eqModeList = new() { Width = 320, Height = 40, IntegralHeight = false, AccessibleName = "EQ mode" };
@@ -3144,12 +3145,13 @@ public sealed class MainForm : Form
     /// and is saved per profile. See <see cref="PeerDspChain"/> / <see cref="PeerShaping"/>.</summary>
     private void BuildPanEqTab()
     {
-        var panel = new TableLayoutPanel { Dock = DockStyle.Fill, Padding = new Padding(12), ColumnCount = 1, RowCount = 8, AutoScroll = true };
+        var panel = new TableLayoutPanel { Dock = DockStyle.Fill, Padding = new Padding(12), ColumnCount = 1, RowCount = 9, AutoScroll = true };
         panel.ColumnStyles.Add(new ColumnStyle(SizeType.Percent, 100));
 
         enableEqForPeersBox.CheckedChanged += (_, _) => { if (!loadingPanEqControls) { MarkProfileDirty(); ApplyAllPeerShaping(); } };
         enablePanForPeersBox.CheckedChanged += (_, _) => { if (!loadingPanEqControls) { MarkProfileDirty(); ApplyAllPeerShaping(); } };
         panEqPeerList.SelectedIndexChanged += (_, _) => OnPanEqPeerSelected();
+        volumeSlider.ValueChanged += (_, _) => OnVolumeChanged();
         panSlider.ValueChanged += (_, _) => OnPanChanged();
         resetPeerEqButton.Click += (_, _) => OnResetPeerEq();
         eqModeList.Items.Add("3 band basic EQ");
@@ -3157,9 +3159,13 @@ public sealed class MainForm : Form
         eqModeList.SelectedIndexChanged += (_, _) => OnEqModeChanged();
 
         var peerLabel = new MnemonicLabel { Text = "Peer to shape (Alt+&U)", AutoSize = true, MnemonicTarget = panEqPeerList };
+        var volumeLabel = new MnemonicLabel { Text = "Vo&lume (Alt+L)", AutoSize = true, MnemonicTarget = volumeSlider };
         var panLabel = new MnemonicLabel { Text = "Pa&n (Alt+N)", AutoSize = true, MnemonicTarget = panSlider };
         var modeLabel = new MnemonicLabel { Text = "EQ &mode (Alt+M)", AutoSize = true, MnemonicTarget = eqModeList };
 
+        var volumeRow = new FlowLayoutPanel { AutoSize = true, WrapContents = false, Margin = new Padding(0) };
+        volumeRow.Controls.Add(volumeLabel);
+        volumeRow.Controls.Add(volumeSlider);
         var panRow = new FlowLayoutPanel { AutoSize = true, WrapContents = false, Margin = new Padding(0) };
         panRow.Controls.Add(panLabel);
         panRow.Controls.Add(panSlider);
@@ -3171,10 +3177,11 @@ public sealed class MainForm : Form
         panel.Controls.Add(enablePanForPeersBox, 0, 1);
         panel.Controls.Add(peerLabel, 0, 2);
         panel.Controls.Add(panEqPeerList, 0, 3);
-        panel.Controls.Add(panRow, 0, 4);
+        panel.Controls.Add(volumeRow, 0, 4);
-        panel.Controls.Add(resetPeerEqButton, 0, 5);
+        panel.Controls.Add(panRow, 0, 5);
-        panel.Controls.Add(modeRow, 0, 6);
+        panel.Controls.Add(resetPeerEqButton, 0, 6);
-        panel.Controls.Add(eqBandsPanel, 0, 7);
+        panel.Controls.Add(modeRow, 0, 7);
+        panel.Controls.Add(eqBandsPanel, 0, 8);
         panEqTabPage.Controls.Add(panel);
 
         RefreshPanEqPeerList();
@@ -3243,10 +3250,13 @@ public sealed class MainForm : Form
         try
         {
             var s = GetOrCreateShaping(selectedShapingKey);
+            volumeSlider.Value = Math.Clamp((int)Math.Round(s.Volume * 100f), 0, 100);
+            UpdateVolumeAccessibleName();
             panSlider.Value = Math.Clamp((int)Math.Round(s.Pan * 50f) + 50, 0, 100);
             UpdatePanAccessibleName();
             eqModeList.SelectedIndex = s.EqMode == PeerEqMode.Advanced10Band ? 1 : 0;
             RebuildEqBandSliders();
+            volumeSlider.Enabled = enabled;
             panSlider.Enabled = enabled;
             resetPeerEqButton.Enabled = enabled;
             eqModeList.Enabled = enabled;
@@ -3279,6 +3289,17 @@ public sealed class MainForm : Form
         panSlider.AccessibleName = $"Pan: {desc}";
     }
 
+    private void OnVolumeChanged()
+    {
+        if (loadingPanEqControls || selectedShapingKey is null) return;
+        GetOrCreateShaping(selectedShapingKey).Volume = Math.Clamp(volumeSlider.Value / 100f, 0f, 1f);
+        UpdateVolumeAccessibleName();
+        ApplyPeerShaping(selectedShapingKey);
+        MarkProfileDirty();
+    }
+
+    private void UpdateVolumeAccessibleName() => volumeSlider.AccessibleName = $"Volume: {volumeSlider.Value} percent";
+
     private void OnEqModeChanged()
     {
         if (loadingPanEqControls || selectedShapingKey is null) return;

src/RemSound.Core/PeerShaping.cs

@@ -16,6 +16,10 @@ public sealed class PeerShaping
     /// <summary>-1 (full left) .. 0 (centre) .. +1 (full right).</summary>
     public float Pan { get; set; }
 
+    /// <summary>Per-peer playback level, 0..1 (1 = 100%, unity). An individual fader for this peer,
+    /// on top of the global volume. Always applied (no master switch); 100% is transparent.</summary>
+    public float Volume { get; set; } = 1f;
+
     /// <summary>Which EQ mode is currently active for this peer.</summary>
     public PeerEqMode EqMode { get; set; } = PeerEqMode.Simple3Band;
 

src/RemSound.Receiver/PeerDspChain.cs

@@ -14,39 +14,46 @@ namespace RemSound.Receiver;
 /// </summary>
 public sealed class PeerDspChain
 {
-    private readonly float panL;
+    // L/R output gains = pan (when enabled) folded together with the per-peer volume (always).
-    private readonly float panR;
+    private readonly float gainL;
-    private readonly bool hasPan;
+    private readonly float gainR;
+    private readonly bool hasGain;
     // Same coefficients on both channels, but each needs its own filter instance because a biquad
     // carries per-channel state. left.Length == right.Length always.
     private readonly BiQuadFilter[] left;
     private readonly BiQuadFilter[] right;
 
-    private PeerDspChain(float panL, float panR, bool hasPan, BiQuadFilter[] left, BiQuadFilter[] right)
+    private PeerDspChain(float gainL, float gainR, bool hasGain, BiQuadFilter[] left, BiQuadFilter[] right)
     {
-        this.panL = panL;
+        this.gainL = gainL;
-        this.panR = panR;
+        this.gainR = gainR;
-        this.hasPan = hasPan;
+        this.hasGain = hasGain;
         this.left = left;
         this.right = right;
     }
 
-    /// <summary>True when this chain would do nothing (pan off/centre and EQ off/flat). Build returns
+    /// <summary>True when this chain would do nothing (unity gain — pan off/centre, volume 100% — and
-    /// null in that case so an unshaped peer's <c>dsp</c> reference is null and it pays nothing.</summary>
+    /// EQ off/flat). Build returns null in that case so an unshaped peer's <c>dsp</c> reference is null
-    public bool IsNoOp => !hasPan && left.Length == 0;
+    /// and it pays nothing.</summary>
+    public bool IsNoOp => !hasGain && left.Length == 0;
 
     /// <summary>Builds a chain for one peer from its saved shaping and the profile's two master
     /// switches. Returns null if there's nothing to do — pan disabled or centred, and EQ disabled or
     /// completely flat. Runs on the UI thread; the result is swapped onto the audio thread atomically.</summary>
     public static PeerDspChain? Build(PeerShaping? shaping, bool applyPan, bool applyEq)
     {
+        // Pan (only when enabled) and the per-peer volume (always applied) fold into one L/R gain.
         // Pan is a balance control: it keeps the peer's stereo image (never sums to mono). Centre is
         // unity on both sides; panning toward one side attenuates the OPPOSITE channel, reaching zero
-        // at the extreme. So a stereo signal just leans left or right rather than collapsing.
+        // at the extreme. Volume then scales both sides. So a stereo signal leans left/right and sits
-        float pan = shaping is null ? 0f : Math.Clamp(shaping.Pan, -1f, 1f);
+        // at the level you set, without ever collapsing to mono.
-        bool hasPan = applyPan && pan != 0f;
+        float pan = applyPan && shaping is not null ? Math.Clamp(shaping.Pan, -1f, 1f) : 0f;
         float panL = pan > 0f ? 1f - pan : 1f;
         float panR = pan < 0f ? 1f + pan : 1f;
+        float vol = shaping is null ? 1f : Math.Clamp(shaping.Volume, 0f, 1f);
+        float gainL = panL * vol;
+        float gainR = panR * vol;
+        bool hasGain = gainL != 1f || gainR != 1f;
 
         var l = new List<BiQuadFilter>();
         var r = new List<BiQuadFilter>();
@@ -64,7 +71,7 @@ public sealed class PeerDspChain
             }
         }
 
-        var chain = new PeerDspChain(panL, panR, hasPan, [.. l], [.. r]);
+        var chain = new PeerDspChain(gainL, gainR, hasGain, [.. l], [.. r]);
         return chain.IsNoOp ? null : chain;
     }
 
@@ -101,12 +108,12 @@ public sealed class PeerDspChain
                 output[2 * f + 1] = sr;
             }
         }
-        if (hasPan)
+        if (hasGain)
         {
             for (int f = 0; f < frames; f++)
             {
-                output[2 * f] *= panL;
+                output[2 * f] *= gainL;
-                output[2 * f + 1] *= panR;
+                output[2 * f + 1] *= gainR;
             }
         }
     }