An SPX file is a Speex audio file saved within an Ogg Vorbis container. Speex is an open source patent-free audio format designed for speech compression. It supports variable bitrate (VBR) encoding and several features not found in other audio codecs. Some examples include embedded encoding, intensity stereo encoding, and voice activity detection.

WavPack lossless audio compression. Note that, when converting .wav to this format and back again, the RIFF header is not necessarily preserved losslessly (though the audio is).