cadence census item 4: doppler velocity operand sample-and-held at 28Hz (gotcha 32) [T2 mechanism / T3 perceptual]. worldLinearVelocity is a raw per-render-frame position derivative; at ~59fps its gait-aliasing noise reached the doppler divisor directly. Fix is consumer-side only per the census: the relative WORLD velocity held per AudioLocation on a 28Hz wall clock; head-frame transform + geometry stay live per call; the mech4 producer untouched. BT_AUD_DOPPLER_HZ override (=0 per-call) + [doppler] receipt under BT_AUD_DOPPLER_LOG (cents/v/d/h/hm2). Measured: clock proven live (55% of calls held vs 0% in control), operand total-variation 67.8 -> 54.2 u/s-per-s (-20%) with std preserved (real stride oscillation kept). T3 flag: cents jitter only -11% on the solo rig because the loud sources ride the player's own entity at d~1 where live near-field geometry dominates -- the nearby-walking-mech warble needs an ear A/B or a 2-node rig. Bonus finding (pre-existing, receipt-exposed, NOT touched): sources linked to child entities of a moving mech read relative v = full ground speed (child worldLinearVelocity=0) -> cents ~ -200 on self-sounds; new census row.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016bw71WVsccjwW7uKRg4aWD

engine/MUNGA/AUDLOC.cpp

@@ -1,3 +1,5 @@
+#include <cstdlib>			// (BT411) getenv -- the 28Hz doppler-operand clock (cadence census item 4)
+#include <map>				// (BT411) per-instance sample-and-hold registry
 #include "munga.h"
 #pragma hdrstop
 
@@ -442,6 +444,45 @@ void
 	);
 	Check(&relative_velocity_temp);
 
+	//
+	// (BT411 cadence census item 4, gotcha 32) 28 Hz SAMPLE-AND-HOLD on the
+	// doppler velocity operand: worldLinearVelocity is a raw per-render-frame
+	// position derivative (the mech4 producer feeds other consumers and is
+	// NOT touched); at ~59 fps its gait-aliasing noise reaches this divisor
+	// directly and warbles dopplerCents per stride.  The pod computed this
+	// once per 28 Hz frame.  Hold the RELATIVE WORLD velocity per instance
+	// on a 28 Hz wall clock; the head-frame transform below stays live per
+	// call (geometry is smooth -- only the noisy operand is clocked).
+	// BT_AUD_DOPPLER_HZ=<hz> overrides (=0 restores per-call sampling).
+	//
+	int dopplerFresh = -1;			// receipt: -1 legacy / 1 sampled / 0 held
+	{
+		static Scalar s_dopHz = -2.0f;
+		if (s_dopHz < -1.0f)
+		{
+			const char *hz = getenv("BT_AUD_DOPPLER_HZ");
+			s_dopHz = (hz != 0 && *hz != '\0') ? (Scalar)atof(hz) : 28.0f;
+		}
+		if (s_dopHz > 0.0f)
+		{
+			struct DopplerHold { DWORD nextMs; Vector3D held; };
+			static std::map<const void *, DopplerHold> s_dopHold;
+			DopplerHold &h = s_dopHold[this];
+			const DWORD now = GetTickCount();
+			if (h.nextMs == 0 || (long)(now - h.nextMs) >= 0)
+			{
+				h.held   = relative_velocity_temp;
+				h.nextMs = now + (DWORD)(1000.0f / s_dopHz);
+				dopplerFresh = 1;
+			}
+			else
+			{
+				relative_velocity_temp = h.held;
+				dopplerFresh = 0;
+			}
+		}
+	}
+
 	relative_velocity.MultiplyByInverse(
 		relative_velocity_temp,
 		head_entity->localToWorld
@@ -473,6 +514,19 @@ void
 		{
 			dopplerCents = cents;
 		}
+
+		// (BT411) doppler receipt -- jitter A/B for the 28Hz operand clock.
+		// hm2 = |held relative WORLD velocity|^2 (the clocked operand itself,
+		// geometry-free); h = 1 fresh sample / 0 held / -1 legacy per-call.
+		if (getenv("BT_AUD_DOPPLER_LOG")) { static int s_dl = 0; if (s_dl++ < 6000)
+			DEBUG_STREAM << "[doppler] t=" << (GetTickCount() % 1000000)
+				<< " this=" << (void *)this
+				<< " cents=" << dopplerCents
+				<< " v=" << speed_of_source
+				<< " d=" << distanceToSource
+				<< " h=" << dopplerFresh
+				<< " hm2=" << relative_velocity_temp.LengthSquared()
+				<< "\n" << std::flush; }
 	}
 	else
 	{