High frequency limit

Perhaps the most commonly known aspect of the psychoacoustic model is that humans cannot hear frequencies above and below certain thresholds; in fact, most humans can only hear frequencies between 20 Hz and 20.5 kHz. So-called "silent" dog whistles[?] exploit this phenomenon by producing sounds at frequencies higher than those audible to humans but well within the range of a dog's hearing. Likewise, when compressing a digital signal, an acoustic engineer[?] can safely assume that any frequency beyond approximately 20.5 kHz will not have any effect on the perceived sound of the finished product, use a band-pass filter to cut everything outside this range. The sound can then be sampled at the stanard CD sample rate of 44.1 kHz, set somewhat higher than the calculated Nyquist-Shannon rate of 41 kHz to allow for the cut-off slope of a reasonable band-pass filter.