Add per-peer listener-side noise gate

Let a listener apply a noise gate to an individual peer's incoming
audio — "fix this person's noisy mic / background hum on my end" —
which is only possible because full-mesh P2P keeps every peer's stream
unmixed locally (server-mixed apps can't do per-listener per-peer DSP).

The DSP is the existing mic NoiseGate reused verbatim: it already
processes i16 frames at a fixed rate with hysteresis/attack/release/
hangover and takes the threshold per-frame. Wiring mirrors per-peer EQ:
- AppConfig.peer_gate map (threshold per peer id; absent/0 = off),
  persisted, never sent over the wire
- CoreCommand::SetPeerGate + Arc<Mutex<HashMap>> shared into the mixer
- a live HashMap<EndpointId, NoiseGate> in the mixer task, created
  lazily and dropped when disabled (no rebuild needed — threshold is
  passed per frame)
- Gate row (threshold slider, "Off" at zero) in each participant card
  next to Vol/Pan/EQ, persisting on release

The gate runs on the raw decoded frame: after the clean multitrack stem
tap (recordings stay ungated) but before volume/EQ, so the threshold
tracks the peer's true signal level regardless of our volume setting.
Same 0..METER_MAX scale as the mic gate.

+2 unit tests (config helper); +1 config back-compat assertion.

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

src/app/mod.rs

@@ -208,6 +208,7 @@ pub enum AppMessage {
     ClearHotkey(HotkeyAction),
     PeerVolumeChanged(EndpointId, f32),
     PeerPanChanged(EndpointId, f32),
+    PeerGateChanged(EndpointId, f32),
     PeerEqChanged(EndpointId, EqBand, f32),
     /// Toggle local mute of a peer (silence them just for us).
     TogglePeerMute(EndpointId),
@@ -478,6 +479,11 @@ impl Default for AppState {
                 let _ = controller.send(CoreCommand::SetPeerVolume(id, *volume));
             }
         }
+        for (peer, threshold) in &config.peer_gate {
+            if let Ok(id) = peer.parse::<EndpointId>() {
+                let _ = controller.send(CoreCommand::SetPeerGate(id, *threshold));
+            }
+        }
         let pixelpass_available =
             crate::screenshare::is_available(config.pixelpass_path.as_deref());
         let all_devices = enumerate_audio_devices();
@@ -761,6 +767,20 @@ fn set_peer_volume_config(config: &mut AppConfig, id: EndpointId, volume: f32) -
     volume
 }
 
+/// Store the per-peer listener noise-gate threshold, clamped to the slider
+/// range. `0.0` means the gate is off, so an at-zero entry is removed rather
+/// than stored. Returns the clamped value.
+fn set_peer_gate_config(config: &mut AppConfig, id: EndpointId, threshold: f32) -> f32 {
+    let threshold = threshold.clamp(0.0, METER_MAX);
+    let key = id.to_string();
+    if threshold <= 0.0 {
+        config.peer_gate.remove(&key);
+    } else {
+        config.peer_gate.insert(key, threshold);
+    }
+    threshold
+}
+
 fn peer_eq_settings(config: &AppConfig, id: &EndpointId) -> EqSettings {
     config
         .peer_eq
@@ -1062,6 +1082,10 @@ fn update(state: &mut AppState, message: AppMessage) -> Task<AppMessage> {
             let pan = set_peer_pan_config(&mut state.config, id, pan);
             let _ = state.controller.send(CoreCommand::SetPeerPan(id, pan));
         }
+        AppMessage::PeerGateChanged(id, threshold) => {
+            let threshold = set_peer_gate_config(&mut state.config, id, threshold);
+            let _ = state.controller.send(CoreCommand::SetPeerGate(id, threshold));
+        }
         AppMessage::PeerEqChanged(id, band, gain_db) => {
             let settings = set_peer_eq_config(&mut state.config, id, band, gain_db);
             let _ = state.controller.send(CoreCommand::SetPeerEq(id, settings));
@@ -3395,6 +3419,28 @@ fn view(state: &AppState) -> Element<'_, AppMessage> {
                 .align_y(iced::alignment::Vertical::Center),
             );
 
+            // Peer noise gate: suppress this peer's background noise on our end.
+            // Threshold is normalized RMS on the same 0..METER_MAX scale as the
+            // mic gate; 0 = off.
+            let current_gate = state.config.peer_gate.get(&peer_key).copied().unwrap_or(0.0);
+            let gate_label = if current_gate <= 0.0 {
+                "Off".to_string()
+            } else {
+                format!("{:.0}%", (current_gate / METER_MAX * 100.0).clamp(0.0, 100.0))
+            };
+            card_content = card_content.push(
+                row![
+                    text("Gate:").size(12).color(color_subtext),
+                    container(text(gate_label).size(11).color(color_subtext))
+                        .width(iced::Length::Fixed(58.0)),
+                    slider(0.0..=METER_MAX, current_gate, move |v| AppMessage::PeerGateChanged(peer_id_clone, v))
+                        .step(0.001)
+                        .on_release(AppMessage::PersistConfig),
+                ]
+                .spacing(8)
+                .align_y(iced::alignment::Vertical::Center),
+            );
+
             let eq = peer_eq_settings(&state.config, peer_id);
             let eq_row = |label: &'static str, band: EqBand, value: f32| -> Element<'_, AppMessage> {
                 row![
@@ -4924,10 +4970,28 @@ impl Program<AppMessage> for Icon {
 mod tests {
     use super::{
         format_duration, initial_window_position, reconnect_attempt_chime, reconnected_chime,
-        set_peer_volume_config, AppConfig, GateMeter, METER_MAX,
+        set_peer_gate_config, set_peer_volume_config, AppConfig, GateMeter, METER_MAX,
     };
     use iroh::SecretKey;
 
+    #[test]
+    fn peer_gate_persists_when_on_and_clears_when_off() {
+        let mut config = AppConfig::default();
+        let id = SecretKey::generate().public();
+
+        // A positive threshold is stored, clamped to the slider's METER_MAX ceiling.
+        let stored = set_peer_gate_config(&mut config, id, 0.05);
+        assert_eq!(stored, 0.05);
+        assert_eq!(config.peer_gate.get(&id.to_string()).copied(), Some(0.05));
+        assert_eq!(set_peer_gate_config(&mut config, id, 99.0), METER_MAX);
+
+        // Zero (or negative) means "gate off" — the entry is removed so the
+        // config doesn't carry a disabled gate.
+        let stored = set_peer_gate_config(&mut config, id, 0.0);
+        assert_eq!(stored, 0.0);
+        assert!(!config.peer_gate.contains_key(&id.to_string()));
+    }
+
     #[test]
     fn peer_volume_persists_non_unity_and_clears_at_unity() {
         let mut config = AppConfig::default();

src/config.rs

@@ -259,6 +259,11 @@ pub struct AppConfig {
     /// string. Local preference only; never sent to peers. Absent entry = unity.
     #[serde(default)]
     pub peer_volume: HashMap<String, f32>,
+    /// Per-peer listener-side noise-gate threshold (normalized RMS, `0.0` = off),
+    /// keyed by peer node id string. Local preference only; never sent to peers.
+    /// Absent entry = gate disabled (pass-through).
+    #[serde(default)]
+    pub peer_gate: HashMap<String, f32>,
     /// Focused app-local keyboard shortcuts.
     #[serde(default)]
     pub hotkeys: crate::hotkeys::HotkeyMap,
@@ -322,6 +327,7 @@ impl Default for AppConfig {
             peer_eq: HashMap::new(),
             peer_pan: HashMap::new(),
             peer_volume: HashMap::new(),
+            peer_gate: HashMap::new(),
             hotkeys: crate::hotkeys::HotkeyMap::default(),
             window_width: default_window_width(),
             window_height: default_window_height(),
@@ -463,6 +469,7 @@ mod tests {
         assert!(deserialized.peer_eq.is_empty());
         assert!(deserialized.peer_pan.is_empty());
         assert!(deserialized.peer_volume.is_empty());
+        assert!(deserialized.peer_gate.is_empty());
         assert_eq!(
             crate::hotkeys::format_binding(
                 deserialized

src/core/messages.rs

@@ -26,6 +26,10 @@ pub enum CoreCommand {
     SetPeerEq(EndpointId, crate::audio::eq::EqSettings),
     /// Listener-side per-peer pan. Local only; never leaves this app instance.
     SetPeerPan(EndpointId, f32),
+    /// Listener-side per-peer noise gate threshold (normalized RMS, `0.0` = off).
+    /// Applies the same smooth gate as the mic path to a peer's incoming audio,
+    /// to suppress their background noise on our end. Local only.
+    SetPeerGate(EndpointId, f32),
     /// Locally mute/unmute a peer: when muted, their audio is decoded (so levels
     /// still show) but not mixed into our output.
     SetPeerMuted(EndpointId, bool),

src/core/mod.rs

@@ -869,6 +869,8 @@ async fn run_core_loop(
     let peer_volumes = Arc::new(Mutex::new(HashMap::<EndpointId, f32>::new()));
     let peer_eq = Arc::new(Mutex::new(HashMap::<EndpointId, EqSettings>::new()));
     let peer_pan = Arc::new(Mutex::new(HashMap::<EndpointId, f32>::new()));
+    // Listener-side per-peer noise-gate thresholds (normalized RMS, 0.0 = off).
+    let peer_gate = Arc::new(Mutex::new(HashMap::<EndpointId, f32>::new()));
     // Peers locally muted by us: decoded for level metering but not mixed.
     let locally_muted = Arc::new(Mutex::new(HashSet::<EndpointId>::new()));
     let mut current_name = "Anonymous".to_string();
@@ -1397,6 +1399,7 @@ async fn run_core_loop(
                 let peer_volumes_mixer = peer_volumes.clone();
                 let peer_eq_mixer = peer_eq.clone();
                 let peer_pan_mixer = peer_pan.clone();
+                let peer_gate_mixer = peer_gate.clone();
                 let locally_muted_mixer = locally_muted.clone();
                 let output_gain_mixer = output_gain.clone();
                 let ui_tx_mixer = ui_tx.clone();
@@ -1413,6 +1416,11 @@ async fn run_core_loop(
                     // Per-peer EQ filter state. Settings are live-cloned each
                     // cycle; state is rebuilt only when a peer's EQ changes.
                     let mut peer_eqs: HashMap<EndpointId, Eq> = HashMap::new();
+                    // Per-peer noise-gate envelope state. The threshold is passed
+                    // per frame (live slider), so the gate is never rebuilt — only
+                    // created once per peer and dropped when the peer leaves.
+                    let mut peer_noise_gates: HashMap<EndpointId, crate::audio::gate::NoiseGate> =
+                        HashMap::new();
                     // When the ring is at/above target we have nothing to do; nap
                     // briefly and re-check. Short enough (relative to the ~60ms
                     // target and ~21ms device quantum) that we always refill well
@@ -1438,6 +1446,7 @@ async fn run_core_loop(
                         let current_volumes = peer_volumes_mixer.lock().await.clone();
                         let current_eq = peer_eq_mixer.lock().await.clone();
                         let current_pans = peer_pan_mixer.lock().await.clone();
+                        let current_gates = peer_gate_mixer.lock().await.clone();
                         let muted_peers = locally_muted_mixer.lock().await.clone();
                         let mut peer_frames: Vec<(Vec<i16>, f32)> = Vec::new();
                         let mut peers_seen = HashSet::new();
@@ -1463,6 +1472,26 @@ async fn run_core_loop(
                                     stems.push((peer_id, frame.clone()));
                                 }
 
+                                // Listener-side per-peer noise gate, applied to the
+                                // raw decoded frame (after the clean stem tap, before
+                                // volume/EQ) so the threshold tracks the peer's true
+                                // signal level regardless of our volume setting. The
+                                // gate's "should transmit" return is irrelevant here —
+                                // we only attenuate. Threshold 0 = off; the gate is
+                                // created lazily and dropped when disabled.
+                                let gate_threshold =
+                                    current_gates.get(&peer_id).copied().unwrap_or(0.0);
+                                if gate_threshold > 0.0 {
+                                    peer_noise_gates
+                                        .entry(peer_id)
+                                        .or_insert_with(|| {
+                                            crate::audio::gate::NoiseGate::new(48_000)
+                                        })
+                                        .process(&mut frame, gate_threshold);
+                                } else {
+                                    peer_noise_gates.remove(&peer_id);
+                                }
+
                                 let vol = current_volumes.get(&peer_id).copied().unwrap_or(1.0);
                                 apply_volume(&mut frame, vol);
 
@@ -1507,6 +1536,8 @@ async fn run_core_loop(
                             }
                         }
                         peer_eqs.retain(|id, _| peers_seen.contains(id) || current_eq.contains_key(id));
+                        peer_noise_gates
+                            .retain(|id, _| peers_seen.contains(id) || current_gates.contains_key(id));
 
                         // Lossless i32 sum, then the limiter applies the master
                         // output gain (in f32, so a boost past the ceiling is
@@ -1884,6 +1915,16 @@ async fn run_core_loop(
                 }
             }
 
+            CoreCommand::SetPeerGate(peer_id, threshold) => {
+                let threshold = threshold.clamp(0.0, 1.0);
+                let mut guard = peer_gate.lock().await;
+                if threshold <= 0.0 {
+                    guard.remove(&peer_id);
+                } else {
+                    guard.insert(peer_id, threshold);
+                }
+            }
+
             CoreCommand::SetPeerMuted(peer_id, muted) => {
                 let mut guard = locally_muted.lock().await;
                 if muted {