Adds null test to artifact.

config.yaml

@@ -38,6 +38,27 @@ artifact_detection:
     energy_variation:
       enabled: true
       threshold_db: 6.0  # Energy change threshold in dB between consecutive windows (detects level changes)
+    null_test:
+      enabled: true
+      # Align Ch2 (DUT) to Ch1 (Loopback), subtract, detect bursts in residual
+      max_lag_ms: 500.0          # Maximum expected delay between channels for alignment search
+      window_ms: 5.0             # Short-time RMS window length for burst detection
+      threshold_factor: 6.0      # Flag windows where residual RMS exceeds baseline × this factor
+      min_burst_ms: 0.5          # Minimum burst duration to report (filters out single-sample spikes)
+      sample_slip_detection: true
+      sample_slip_window_ms: 50.0  # Correlation window for xcorr-based lag tracking (fallback only)
+      # Sync marker: one chirp burst at the start and one at the end of the played signal.
+      # Marker-based alignment is immune to periodic-signal ambiguity (e.g. pure sine).
+      # Sample slip detection compares the lag at the start marker vs. the end marker.
+      marker_duration_sec: 0.05      # Length of each chirp marker burst
+      marker_first_offset_sec: 0.5   # Offset from signal start (and from signal end) for markers
+      marker_f0: 200.0           # Marker chirp start frequency (Hz)
+      marker_f1: 16000.0         # Marker chirp end frequency (Hz) — wider BW = sharper correlation peak
+      marker_amplitude: 0.7      # Marker amplitude (mixed on top of test tone)
+      # Sample slip threshold: only report if inter-marker lag deviates from median by >= this many samples.
+      # Rule of thumb: peak timing precision ≈ 1 / (marker_f1 - marker_f0) * sample_rate
+      # With 200-16000 Hz BW at 44100 Hz: precision ≈ 3 samples → min_slip_samples = 5 gives good margin.
+      min_slip_samples: 5
 
 latency:
   max_std_dev_ms: 1.0  # Maximum allowed std deviation; test fails if exceeded