Mix: clamp clip-FX gain and send-level automation (fixes #884)

A shared session or an MCP clip.effects_set could store clip-FX gain or a
send-level automation point far above any fader (up to the +200 dB cap in
db_to_gain). Clamp clip-FX gain to the slider's +24 dB, send-level lanes to
+12 dB, and every loaded automation point to its AutoParam range on sanitize.

Co-Authored-By: opencode beam-free <noreply@opencode.ai>
Co-Authored-By: MiniMax M3 <noreply@minimax.io>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/clip_more.rs

@@ -196,8 +196,14 @@ fn unloop(e: &mut Engine, p: &Value) -> Result<Value> {
 fn effects_set(e: &mut Engine, p: &Value) -> Result<Value> {
     let ids = clip_ids_param(e, p);
     let params = p.get("params").and_then(Value::as_object).ok_or_else(|| bad("clip.effects_set", "`params` must be an object of numbers"))?;
-    let vals: Vec<(String, f64)> =
-        params.iter().filter_map(|(k, v)| v.as_f64().filter(|x| x.is_finite()).map(|x| (k.chars().take(64).collect(), x))).collect();
+    let vals: Vec<(String, f64)> = params
+        .iter()
+        .filter_map(|(k, v)| v.as_f64().filter(|x| x.is_finite()).map(|x| (k.chars().take(64).collect(), x)))
+        .map(|(k, v)| {
+            let v = if k == "gain" { v.clamp(f64::from(soundcraft_dsp::MIN_DB), f64::from(soundcraft_mix::CLIP_FX_MAX_GAIN_DB)) } else { v };
+            (k, v)
+        })
+        .collect();
     let s = e.session_mut();
     for c in &ids {
         for (k, v) in &vals {
@@ -316,6 +322,13 @@ mod tests {
         (Engine::new(s), t, ids)
     }
 
+    #[test]
+    fn effects_set_caps_gain() {
+        let (mut e, _t, ids) = engine_with(&[(0, 100, 0)]);
+        e.execute("clip.effects_set", &json!({"clip": ids[0].0, "params": {"gain": 500.0}})).unwrap();
+        assert_eq!(e.session().edit.values.get(&format!("clip_fx.{}.gain", ids[0].0)).copied(), Some(24.0));
+    }
+
     #[test]
     fn unloop_removes_copies() {
         let (mut e, t, ids) = engine_with(&[(0, 100, 0), (100, 100, 0), (200, 100, 0), (300, 100, 50)]);

crates/mix/src/lib.rs

@@ -76,6 +76,11 @@ pub fn main_channels(s: &Session) -> usize {
 /// (insert slots use their index).
 pub const INSTRUMENT_SLOT: usize = usize::MAX;
 
+/// Top of the clip effects gain slider; a stored or wired gain is clamped to it (#884).
+pub const CLIP_FX_MAX_GAIN_DB: f32 = 24.0;
+/// Top of a send fader, the same +12 dB `AutoParam::SendLevel` ranges up to (#884).
+pub const SEND_LEVEL_MAX_DB: f32 = 12.0;
+
 /// Hosted third-party plugin ids (CLAP or VST3): created off the audio thread in realtime use.
 pub fn is_third_party(id: &str) -> bool {
     id.starts_with(soundcraft_clap_host::ID_PREFIX)
@@ -1279,7 +1284,7 @@ impl ClipFx {
                     c.set_param(p, v);
                 }
             } else if k == "gain" {
-                self.gain_db = v;
+                self.gain_db = if v.is_nan() { 0.0 } else { v.clamp(soundcraft_dsp::MIN_DB, CLIP_FX_MAX_GAIN_DB) };
             }
         }
     }
@@ -1967,7 +1972,7 @@ fn send_level(t: &Track, i: usize, base: f32, pos: Samples) -> f32 {
         && let Some(l) = t.lane(&AutoParam::SendLevel(u8::try_from(i).unwrap_or(0)))
         && !l.points.is_empty()
     {
-        return l.value_at(pos, base);
+        return l.value_at(pos, base).clamp(soundcraft_dsp::MIN_DB, SEND_LEVEL_MAX_DB);
     }
     base
 }

crates/model/src/session.rs

@@ -626,6 +626,8 @@ impl Session {
             }
             for l in &mut t.automation {
                 l.points.retain(|p| p.value.is_finite());
+                let (lo, hi, _) = l.param.range();
+                l.points.iter_mut().for_each(|p| p.value = p.value.clamp(lo, hi));
                 l.points.iter_mut().for_each(|p| bound(&mut p.at));
                 l.points.sort_by_key(|p| p.at);
             }