From 36d42933108104519da62cbd7373d5129bbc680f Mon Sep 17 00:00:00 2001
From: Zeyu Yang <40936154+zeyuyang42@users.noreply.github.com>
Date: Fri, 16 Oct 2026 21:19:54 +0200
Subject: [PATCH] core: crest factor outputs 0 on silence instead of NaN

peak / RMS with both at 0 is NaN, and the NaN rode into every object
downstream once the input went quiet. Report 0 like the spectral
features do with no energy. std::fabs instead of abs on a double.

Max: zerr.features~ cf no longer poisons zerr.envelopes~ on silence.
Pd: zerr_features~ cf, same. Notes added to max-v0.3.0.md and pd-next.md.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
---
 core/src/features/crestfactor.cpp | 6 ++++--
 docs/releases/max-v0.3.0.md       | 2 ++
 docs/releases/pd-next.md          | 2 ++
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/core/src/features/crestfactor.cpp b/core/src/features/crestfactor.cpp
index 48a9d00..8d67ee3 100644
--- a/core/src/features/crestfactor.cpp
+++ b/core/src/features/crestfactor.cpp
@@ -28,14 +28,16 @@ void CrestFactor::extract()
     for (int i = 0; i < x_size; ++i) {
         square_sum += x[i] * x[i];
 
-        peak_tmp = abs(x[i]);
+        peak_tmp = std::fabs(x[i]);
         peak_max = peak_tmp > peak_max ? peak_tmp : peak_max;
     }
 
     square_sum  = square_sum / x_size;
     square_root = std::sqrt(square_sum);
 
-    crr_y = peak_max / square_root;
+    // Silence: peak and RMS are both 0 and the ratio would be NaN, which then rides into
+    // every object downstream. Report 0, like the spectral features do with no energy.
+    crr_y = square_root > 0.0 ? peak_max / square_root : 0.0;
 }
 
 void CrestFactor::reset() { _reset_param(); }
diff --git a/docs/releases/max-v0.3.0.md b/docs/releases/max-v0.3.0.md
index a296be3..1963843 100644
--- a/docs/releases/max-v0.3.0.md
+++ b/docs/releases/max-v0.3.0.md
@@ -43,6 +43,8 @@ First release of Zerr* for Max, as a package for Max 9 on Apple Silicon (arm64,
   silently on the audio thread. (#30)
 - `zerr.combinator~` builds the core combinator for real; before #19 the mode argument was parsed
   and discarded. (#19)
+- `zerr.features~ cf` outputs 0 on silence instead of NaN (0/0), which used to poison every
+  object downstream once the input went quiet.
 
 ## Build and tooling
 
diff --git a/docs/releases/pd-next.md b/docs/releases/pd-next.md
index ec5e45b..c7067af 100644
--- a/docs/releases/pd-next.md
+++ b/docs/releases/pd-next.md
@@ -11,3 +11,5 @@ since 2026-10-15 only; everything earlier since `v0.2` still has to be enumerate
 - `zerr_features~` says why it refuses a block size instead of printing the two numbers:
   the block must be 1 to 2048 samples, the analysis window, and the sample rate non-zero (#43).
   The help patch documents the limit.
+- `zerr_features~ cf` outputs 0 on silence instead of NaN (0/0), which used to poison every
+  object downstream once the input went quiet.