from usbd_audio.h:242
typedef struct
{
uint8_t bLength;
uint8_t bDescriptorType;
uint8_t bDescriptorSubtype;
uint8_t bFormatType;
uint8_t bNrChannels;
uint8_t bSubFrameSize;
uint8_t bBitResolution;
uint8_t bSamFreqType;
uint8_t tSamFreq2;
uint8_t tSamFreq1;
uint8_t tSamFreq0;
} USBD_SpeakerIIIFormatIfDescTypeDef;