Thanks for the information Matthew. The samples are stored in 24 bit contains and the audio uses two channels - thus the block alignment is 6. We're using WAVEFORMATEX as the pFormat parameter in the call to IsFormatSupported(). We set the structure up as follows: wFormatTag = 1 (WAVE_FORMAT_PCM) nChannels = 2 nSamplesPerSec = 48000 nAvgBytesPErSec = 288000 nBlockAlign = 6 wBitsPerSample = 24 cbSize = 0 Thanks so much for the help!