Use an odd number of taps for PAL/NTSC LPFs #424
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FIRFilter is only intended to work with an odd number of taps -- with an even number of taps, the output is delayed by half a sample. Fixing this means ld-analyse's LPF mode is now aligned with the other two modes, and produces very (very!) slightly better output from ld-dropout-correct.
atsampson
added
enhancement
ld-decode-tools
simoninns
approved these changes
Jan 23, 2020
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I'd wondered why the LPF view in ld-analyse didn't quite line up with the other two views - it's because the filters had an even number of taps, so FIRFilter can't compensate for the leftover 0.5-sample delay.
Switch from 6 to 7 taps, and add an assert to FIRFilter to catch this in the future.
@simoninns - this might affect the DoD stuff you're working on; 5 taps would also work if you'd prefer that to 7.