Sample rate conversion library for audio data
http://www.mega-nerd.com/SRC/download.html

Secret Rabbit Code is a sample rate converter for audio. It is capable
of arbitrary and time varying conversions. It can downsample by a
factor of 12 and upsample by the same factor. The ratio of input and
output sample rates can be a real number. The conversion ratio can
also vary with time for speeding up and slowing down effects.