SoX Resampler Library Copyright (c) 2007-18 robs@users.sourceforge.net
The SoX Resampler library `libsoxr' performs one-dimensional sample-rate
conversion -- it may be used, for example, to resample PCM-encoded audio.
For higher-dimensional resampling, such as for visual-image processing, you
should look elsewhere.
It aims to give fast¹ and very high quality² results for any constant
(rational or irrational) resampling ratio. Phase-response, preserved
bandwidth, aliasing, and rejection level parameters are all configurable;
alternatively, simple `preset' configurations may be selected. A
variable-rate resampling mode of operation is also included.
The resampler is currently available either as part of `libsox' (the audio
file-format and effect library), or stand-alone as `libsoxr' (this package).
The interfaces to libsox and libsoxr are slightly different, with that of
libsoxr designed specifically for resampling. An application requiring
support for other effects, or for reading-from or writing-to audio files or
devices, should use libsox (or other libraries such as libsndfile or
libavformat).
Libsoxr provides a simple API that allows interfacing using the most
commonly-used sample formats and buffering schemes: sample-formats may be
either floating-point or integer, and multiple channels either interleaved
or split in separate buffers. The API is documented in the header file
`soxr.h', together with sample code found in the 'examples' directory.
For compatibility with the popular `libsamplerate' library, the header file
`soxr-lsr.h' is provided and may be used as an alternative API.³ Note
however, that libsoxr does not provide a full emulation of libsamplerate
and that using this approach, only a sub-set of libsoxr's features are
available.
The design was inspired by Laurent De Soras' paper `The Quest For The
Perfect Resampler', http://ldesoras.free.fr/doc/articles/resampler-en.pdf;
in essence, it combines Julius O. Smith's `Bandlimited Interpolation'
technique (https://ccrma.stanford.edu/~jos/resample/resample.pdf) with FFT-
based over-sampling.
Note that for real-time resampling, libsoxr may have a higher latency
than non-FFT based resamplers. For example, when using the `High Quality'
configuration to resample between 44100Hz and 48000Hz, the latency is
around 1000 output samples, i.e. roughly 20ms (though passband and FFT-
size configuration parameters may be used to reduce this figure).
For build and installation instructions, see the file `INSTALL'; for
copyright and licensing information, see the file `LICENCE'.
For support and new versions, see https://soxr.sourceforge.net
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¹ For example, multi-channel resampling can utilise multiple CPU-cores.
² Bit-perfect within practical occupied-bandwidth limits.
³ For details of that API, see http://www.mega-nerd.com/SRC/api.html.
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