diff --git a/src/AquariumSynth.Dsl/FaustExport.cs b/src/AquariumSynth.Dsl/FaustExport.cs
index 7d22001..c059146 100644
--- a/src/AquariumSynth.Dsl/FaustExport.cs
+++ b/src/AquariumSynth.Dsl/FaustExport.cs
@@ -124,7 +124,7 @@ public static class FaustEmitter
         source.AppendLine($"{name}_colored = ({name}_osc * (1.0 - {noiseMix}) + no.noise * {noiseMix});");
         source.AppendLine($"{name}_driven = ma.tanh({name}_colored * (1.0 + {driveExpression} * 12.0)) / ma.tanh(1.0 + {driveExpression} * 12.0);");
         source.AppendLine($"{name}_folded = {name}_driven * (1.0 - {foldExpression}) + fold({name}_driven * (1.0 + {foldExpression} * 3.5)) * {foldExpression};");
-        source.AppendLine($"{name}_filtered = {name}_folded : {lowpass} : fi.highpass(1, max(20.0, {hpf} * 8000.0));");
+        source.AppendLine($"{name}_filtered = {name}_folded : {lowpass} : fi.highpass(1, max(5.0, ({hpf}) * ({hpf}) * 7000.0));");
         if (voice.Phaser.OffsetSeconds != 0 || voice.Phaser.RampSecondsPerSecond != 0)
         {
             var delay = $"min(2047.0, max(0.0, abs({F(voice.Phaser.OffsetSeconds)} + {F(voice.Phaser.RampSecondsPerSecond)} * age) * ma.SR))";
diff --git a/state/evidence.jsonl b/state/evidence.jsonl
index ec6a6ad..0ac2192 100644
--- a/state/evidence.jsonl
+++ b/state/evidence.jsonl
@@ -1,3 +1,4 @@
 {"kind":"migration","lesson":"The C# repo must own reusable authoring, analysis, preset, scoring, and Faust-generation behavior; only the Rust renderer/runtime and experimental compiler branch are intentionally left behind.","source":"user direction and migration pass through commit 3246672"}
 {"kind":"realtime","lesson":"Runtime-facing audio code must avoid unbounded operations: allocation, locks, I/O, console output, OS calls, and context switches do not belong in audio callbacks.","source":"PortAudio callback documentation"}
 {"kind":"dsp_graph","lesson":"Treat patch scripts as deterministic dataflow graphs with explicit rate and block semantics; terse syntax is acceptable only when lowering remains inspectable.","source":"Pure Data block/subpatch model and Faust block-diagram model"}
+{"kind":"sfxr_parity","lesson":"SFXR normalized filter values are not linear cutoff frequencies. In Faust export, small SFXR high-pass values must remain very low; mapping hpf directly to thousands of Hz removes the body of pickup, jump, powerup, and blip presets while still leaving them audible enough for weak tests to pass.","source":"Aquarium engine native Faust parity test against C# SFXR reference renderer"}