By "frequency data", do you mean FFT data? If so, you can use BASS_ChannelGetData to get that from the "decoding channel" that you created with the BASS_STREAM_DECODE flag. To process an entire file, you might do something like this...
decoder=BASS_StreamCreateFile(FALSE, filename, 0, 0, BASS_STREAM_DECODE); // create a decoding channel for a file
while (BASS_ChannelIsActive(decoder)) { // not at the end yet
float fft[256];
BASS_ChannelGetData(decoder, fft, BASS_DATA_FFT512); // perform a 512 sample FFT
// do something with the FFT data in the "fft" array here
}
Please see the BASS_ChannelGetData documentation for details on that.
