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51 lines
2.6 KiB
Plaintext
51 lines
2.6 KiB
Plaintext
SoX Resampler Library Copyright (c) 2007-12 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 be fast (e.g. multi-channel resampling can utilise multiple
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CPU-cores), high-quality (i.e. bit-perfect up to 32-bits, for occupied-
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bandwidths up to 98%¹), and to allow any rational or irrational resampling
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ratio. Phase-response, preserved bandwidth, aliasing, and rejection level
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parameters are all configurable; alternatively, simple `preset'
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configurations may be selected.
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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 any commonly-
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used sample format or buffering scheme: clients may use either floating-
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point or integer sample formats, and, in the case of multiple channels,
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either channel-interleaved, or split channels. The API is currently
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documented in the header file `soxr.h' and by example code in the 'examples'
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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. For details
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of that API, see http://www.mega-nerd.com/SRC/api.html. Note however, that
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libsoxr does not provide a full emulation of libsamplerate; in particular,
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`vari-speeding' is not supported.
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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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The resampler 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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it combines Julius O. Smith's `Bandlimited Interpolation' technique
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(https://ccrma.stanford.edu/~jos/resample/resample.pdf) with FFT-based
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over-sampling.
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Its use of FFTs means that, for real-time resampling, libsoxr may have a
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higher latency than non-FFT based resamplers. E.g. when using the `High
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Quality' configuration to resample between 44100Hz and 48kHz, the latency is
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around 1000 output samples, i.e. roughly 20 ms.
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¹ Note that no practical resampler can be bit-perfect to 100% bandwidth.
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