The VOC format is an old sound format developed by Creative Labs. It is based on small blocks of sound data, each with their own properties. ZDoom only supports two of the eight "codecs" defined by the format: codec 0 (8-bit unsigned PCM) and codec 4 (16-bit signed PCM); the ADPCM, A-law and μ-law codecs are not supported but they were very seldom used. ZDoom also requires that all sound blocks use the same sample rate.
This format is supported for sound, but not for music.