tns: fix inverted adaptive TNS order for low-bitrate encoders (D4)#108
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tns: fix inverted adaptive TNS order for low-bitrate encoders (D4)#108nschimme wants to merge 3 commits into
nschimme wants to merge 3 commits into
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- Refactored bmask() in quantize.c into a one-pass loop with energy floors. - Ported spectral whitening and adaptive thresholds to tns.c. - Optimized autocorrelation and added safety clamping for TNS coefficients. - Enabled TNS by default and adjusted PNS levels. - Reworked all comments to match a professional signal engineering style. - Added TNS_TUNING.md documenting parameter derivations.
At voip rates (<96 kbps/ch), the old 3-tier table assigned order 12, the highest analysis cost. Correct to order 8 at <96 kbps and 12 at >=96 kbps — matching the CPU budget constraint where lower bitrates can afford less filter precision. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Summary
tnsMaxOrderLongassignment inTnsInit: at voip bitrates (<96 kbps/ch) the encoder now uses order 8 instead of order 12, reducing autocorrelation and Levinson-Durbin costMotivation
This is the D4 arm from the TNS Phase D investigation. Local benchmark on 449 files (TCD-VOIP + music_low, 16 kbps):
D4 fixes C_24_ECHO_FA (+0.183 vs base, was −0.224) and reduces encode time by reducing filter order at voip rates.
Test plan
🤖 Generated with Claude Code