libfresample/comparison.txt at master · depp/libfresample · GitHub

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Comparison and resources
========================

Comparisons of resamplers
-------------------------

Resampling comparisons: http://src.infinitewave.ca/

Tests designed by Alexey Lukin, who is associated with iZotope and
RightMark.

Note the highest quality converters, according to this test:

      Adobe Audition 5.5 and CS6
      Awave Studio 10.3
      eac3to (SSRC)
      FinalCD 0.12
      IRCAM SuperVP (160dB SNR)
      iZotope 64 bit SRC Steep, No Alias
  [1] iZotope 64 bit SRC Intermed. Phase
      iZotope RX Adv 2 (High Steepness)
      libfsrc (alpha)
  [2] r8brain Free
  [3] r8brain Pro Minimum Phase
      Signalyst (Sinc)
      Sound Sculptor Pro 3.0.2
      SoX 14.4 VHQ Linear Phase
  [3] SoX 14.4 VHQ Intermediate Phase
  [3] SoX 14.4 VHQ Minimum Phase
      Wave Editor 1.4.6 (Steep No Aliasing)

All converters in the list show linear phase, with the following
exceptions:

  [1] mostly linear phase filter, up to around 15 kHz
  [2] linear phase filter, but inverted output
  [3] not linear phase filter (pronounced impulse response asymmetry)

The above comparison has the drawback that it is visual.  Invisible
artifacts might be audible, and visible artifacts might be inaudible.
In particular, the graphs might show artifacts which are masked by the
signal, at least to the human ear.  The author of the test also claims
that the effect of ringing is "smearing of the stereo image and
reducing the clarity of bass", but I am skeptical.

As an example, the "Secret Rabbit Code 0.1.3 (Best Sinc)" has visible
artifacts, but it appears to be harmonics below -150 dB, which are
almost certainly inaudioble.  "Secret Rabbit Code 0.1.2 (Best Sinc)"
shows nasty looking artifacts, but the harmonics are below -100 dB.
The filters which score the best appear somewhat overdesigned.  For
example, libfsrc has a transition band that looks to be about 200-300
Hz wide, which one might call "unreasonably sharp".

RightMark
---------

RightMark: http://audio.rightmark.org/

RightMark is used for testing audio quality and correctness, but I'm
not sure if it can be used to test a program's sample rate conversion.
It's commercial, and only available for Windows.

libfsrc
-------

libfsrc: http://libfsrc.sourceforge.net/ (GPL)

This appears to be a very high quality resampler, which uses a
different (more sophisticated) filter design technique than windowing.
It's GPL, but not release quality yet.

SoX
---

SoX: http://sox.sourceforge.net/ (GPL)

SoX is also GPL, and includes a high quality resampler.  I'm not sure
what algorithm SoX uses.

Secret Rabbit Code
------------------

Secret Rabbit Code: http://www.mega-nerd.com/SRC/ (GPL)

Secret Rabbit Code includes a program for testing sample rate
conversion, which calculates bandwidth and SNR.