The SoX Resampler library `libsoxr'

It performs one-dimensional sample-rate conversion,
may be used, for example, to resample PCM-encoded audio.

This library aims to give fast and high quality 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.      An
experimental, variable-rate resampling mode of operation is also included.

WWW: http://sourceforge.net/p/soxr/