"Hein ten Horn" wrote in message
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So take another example: 25000 Hz and 25006 Hz.
Again, constructive and destructive interference produce 6 Hz
amplitude variations in the air.
But, as we can't hear ultrasonic frequencies, we will not produce
a 25003 Hz perception in our brain. So ther's nothing to hear,
no tone and consequently, no beat.
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If one looks at an oscilloscope of the audio converted to voltage, one still
can see the 6Hz variations on the 25003 Hz and still refers to those as tone
and beat. These exist in mathematically formulation of the resulting
waveforms not just as something in the brain.