In {HEAD ~ synchronism} with the frequency fm, {TAIL ~ 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 a filtered signal alternating at the frequency fm between values related to sin fx and cos fx  
In { HEAD ~ synchronism } with the frequency fm , { TAIL ~ 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 a filtered signal alternating at the frequency fm between values related to sin fx and cos fx
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