Chad 2026.06.21 ntscfixes#1048
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… offset The old shift33 constant (83° in radians, treated as output samples by apply_offsets) had a unit mismatch that made the math opaque and produced ~139° median burst phase instead of the correct ~147°. Replaced with a direct formula: fsc_phase_deg=122.5 converted to input samples via the subcarrier period. Includes investigation notes documenting what was ruled out (filter phase, comb filter, sinc interpolation, burst locking damping, outlinelen rounding, etc). Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
…row audio notch Three changes to eliminate ~10° differential phase between burst (0 IRE) and 70 IRE color bar measurements: - Split RF BPF into independent HP order 2 / LP order 3 (was single BPF order 4), reducing sideband asymmetry on the low-frequency skirt - Generalize post-demod group delay equalizer for NTSC (IEC 60857 9.1.7) in addition to PAL (IEC 60856 9.1.6), correcting LPF undershoot across the chroma band - Narrow NTSC audio notch width from 350 kHz to 200 kHz (matching PAL), cutting the notch filters' group delay contribution to differential phase - Recalibrate fsc_phase_deg from 122.5° to 117.25° for the new filter chain Result on he010 color bar disc (30 frames): DP reduced from ~10° to 0.7°, with Phase (70 IRE bar) at 147.7° and MedPhase (burst) at 147.0°. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Checklist
Description
Adapt dp11's filtering improvements to NTSC.
Motivation
Fixes color phase at different amplitudes.
Related Issues
Changes Made
Testing
pytest --output-on-failure)Screenshots (if applicable)
Additional Notes
The color decoder should detect the reduced amplitude (which was never quite full anyway) and boost decoding accordingly.