Input/output sample correlation is achieved through the use of first and second correlation tags appended to input and output buffers, respectively. As an output buffer of output samples is prepared, the first correlation tag identifies one of tie output samples in that buffer. As input samples are input and placed into an input buffer, a second correlation tag is appended to the input buffer which identifies the input sample that is input at the time the output sample identified by the first correlation tag is output. Accordingly, a correlation between input and output samples can be used in an echo cancellation operation or the like.