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hifi-decode: Do FFT in power of 2#204

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harrypm merged 4 commits intooyvindln:vhs_decodefrom
eshaz:hifi-decode-fft-power-of-2
Mar 23, 2025
Merged

hifi-decode: Do FFT in power of 2#204
harrypm merged 4 commits intooyvindln:vhs_decodefrom
eshaz:hifi-decode-fft-power-of-2

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@eshaz eshaz commented Mar 22, 2025 •
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Fixes

  • Disable integer division for overlap when input sample rate is not dividable by the output sample rate, i.e. --cxadc
  • Tune block overlap logic to be a bit more accurate.
  • Calculate peak gain only for audio that is written to the output file.

Enhancements

  • Update intermediate frequency audio sample rate so FFT operations operate on data chunks sized in a power of 2 for efficiency.

Benchmark

$ ffmpeg -i test.rf.flac -f s16le -acodec pcm_s16le - | \
~/git/vhs-decode/hifi-decode -n -t 32 -f 20 --overwrite --auto_fine_tune off --normalize - test.hifi.flac
Computer Specs 
$ lscpu
CPU(s):                   192
  On-line CPU(s) list:    0-191
Vendor ID:                GenuineIntel
  Model name:             Intel(R) Xeon(R) CPU E7-8890 v4 @ 2.20GHz
    CPU family:           6
    Model:                79
    Thread(s) per core:   2
    Core(s) per socket:   24
    Socket(s):            4
    Stepping:             1

Before Changes

- Decoding speed: 61733 kFrames/s (1.54x), 0 blocks enqueued
- Input position: 0:29:28.403
- Audio position: 0:29:28.403
- Audio buffer  : 0:00:00.000
- Wall time     : 0:19:05.831

Peak gain is 72.92%. Adjusting by 137.04%, please wait...
Progress [########################################] 100.00%

Decode finished, seconds elapsed: 1164
Decode finished successfully

After Changes

- Decoding speed: 76518 kFrames/s (1.91x), 0 blocks enqueued
- Input position: 0:29:28.403
- Audio position: 0:29:28.403
- Audio buffer  : 0:00:00.000
- Wall time     : 0:15:24.437

Peak gain is 71.56%. Adjusting by 139.65%, please wait...
Progress [########################################] 100.00%

Decode finished, seconds elapsed: 945
Decode finished successfully

@harrypm harrypm merged commit ee8b360 into oyvindln:vhs_decode Mar 23, 2025
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2 participants

@eshaz @harrypm