In synchronism with the frequency fm, any components of the mixed signal that are related to sin fx and cos fx, where fx =|fi fr |, provided that fx is substantially equal to or less than fb /2, are filtered to provide {HEAD ~ a filtered signal} alternating at {TAIL ~ the frequency fm} between values related to sin fx and cos fx  
In synchronism with the frequency fm , any components of the mixed signal that are related to sin fx and cos fx , where fx = |fi fr | , provided that fx is substantially equal to or less than fb /2 , are filtered to provide { HEAD ~ a filtered signal } alternating at { TAIL ~ the frequency fm } between values related to sin fx and cos fx
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