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