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