For audio decoding, the butterfly unit determines combinations of components of a frequency domain vector to reduce the number of {HEAD ~ multiplies} required to transform to {TAIL ~ the time domain}  
required to transform to
For audio decoding , the butterfly unit determines combinations of components of a frequency domain vector to reduce the number of { HEAD ~ multiplies } required to transform to { TAIL ~ the time domain }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH