The WAVEFORMATEX structure is a Win32 structure which is used to describe the format of a sound.
The structure definition contained in the DirectSound section of the DirectX SDK is:

typedef struct
{
WORD wFormatTag;
WORD nChannels;
DWORD nSamplesPerSec;
DWORD nAvgBytesPerSec;
WORD nBlockAlign;
WORD wBitsPerSample;
WORD cbSize;
} WAVEFORMATEX;