Feedforward active noise cancellation in headphones operates against one of the tightest physical latency ceilings in commercial computing: with sound traveling through air at 343 m/s, an acoustic disturbance takes approximately 44 microseconds to physically traverse the 15 mm gap between an exterior microphone and the ear canal. Sampling, ADC conversion, DSP phase inversion, and speaker diaphragm actuation must complete entirely within that 40-microsecond window before the pressure wavefront passes the eardrum. wikipedia.org