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From: Ariff Abdullah <ariff@FreeBSD.org>
Date: Sun, 5 Jul 2009 18:15:06 +0000 (UTC)
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Subject: cvs commit: src/sys/dev/sound/pcm feeder_rate.c src/sys/tools/sound
 feeder_rate_mkfilter.awk
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ariff       2009-07-05 18:15:06 UTC

  FreeBSD src repository

  Modified files:
    sys/dev/sound/pcm    feeder_rate.c 
    sys/tools/sound      feeder_rate_mkfilter.awk 
  Log:
  SVN rev 195378 on 2009-07-05 18:15:06Z by ariff
  
  - Increase dynamic range of filter coefficients from 28bit to 30bit.
    This cause dramatic effect in overall precision and conversion quality
    by pushing down most aliasing artifacts around -180 dB.
  
    Spectrogram analysis/comparison:
  
          http://people.freebsd.org/~ariff/z_comparison/z_28vs30/
  
  - Guard against possible 64bit overflow during accumulation process by
    slightly normalize and saturate sample and coefficient multiplication,
    possible during extreme 32bit downsampling (eg. 380KHz -> 8KHz) with
    custom preset that require more than ~7000 taps filter (which is
    overkill).
  
  - Add knobs through FEEDER_RATE_PRESETS to set dynamic range of filter
    coefficients/accumulator and prefered polynomial interpolator:
  
          COEFFICIENT_BIT:X
          (where 1 <= X <= 30, default: 30)
  
          ACCUMULATOR_BIT:X
          (where 32 <= X <=64, default: 58)
  
          INTERPOLATOR:I
          (where I = ZOH, LINEAR, QUADRATIC, HERMITE, BSPLINE,
                     OPT32X, OPT16X, OPT8X, OPT4X, OPT2X)
  
  Approved by:    re (kib)
  
  Revision  Changes    Path
  1.27      +10 -10    src/sys/dev/sound/pcm/feeder_rate.c
  1.4       +110 -3    src/sys/tools/sound/feeder_rate_mkfilter.awk