Since {HEAD ~ only four parameters} are needed to specify {TAIL ~ the input signal}, the signal is easy to construct, and it thus practical for use in high density disk drive applications 
are needed to specify
Since { HEAD ~ only four parameters } are needed to specify { TAIL ~ the input signal } , the signal is easy to construct , and it thus practical for use in high density disk drive applications
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH