# Can someone please explain the difference between sound frequency and, say, beats per second?

I'm sure this is a monumentally stupid question buy I'm just stumped. I'm not sure how sound frequency is different than beats per sec from a physics perspective. Humans can hear down to 20HZ which is 20 compression waves per second isnt it? But when I tap something at 20 beats per second I'm also creating 20 compression waves per second. Clearly I can hear 20 beats per second and it only becomes more distinguishable as I go lower, so I'm clearly wrong on my interpretation, I'm just not sure how. I know I could tap a 440 Hz tuning fork, allow it to ring for 500ms, do that 20 times per second, and I'd have 20 cycles per sec samples of a 440 cycles per second sound, but if they're both compression waves, what's going on?

• Re, "I'm not sure how sound frequency is different than beats per sec from a physics perspective." Why do you think it is different? The Earth's atmosphere is capable of transmitting so-called "infrasound" signals, where the frequency is expressed in seconds per cycle instead of the other way around, over distances of many miles. Just because your ears are not equipped to perceive infrasound does not mean that the physical principles that underlie it are any different from the physical principles that underlie the sounds that you are able to hear. Commented Aug 2, 2019 at 13:01
• P.S., Any periodic signal can be mathematically decomposed into a sum of sinusoids of different frequencies. Your ears are equipped to actually do that--they contain thousands tiny receptors, each of which resonates with a different frequency. If a sound continuously stimulates some combination of those receptors, then you perceive it as a continuous combination of tones. If the sound contains frequencies lower than any that your ears are equipped to perceive as distinct tones, then you perceive that as the sound changing over time. Commented Aug 2, 2019 at 13:09