shorten reduces the size of waveform files (such as audio) using Huffman
coding of prediction residuals and optional additional quantisation. In
lossless mode the amount of compression obtained depends on the nature
of the waveform. Those composing of low frequencies and low amplitudes
give the best compression, which may be 2:1 or better. Lossy compression
operates by specifying a minimum acceptable segmental signal to noise
ratio or a maximum bit rate. Lossy compression operates by zeroing the
lower order bits of the waveform, so retaining waveform shape.