Columns Retired Columns & Blogs |
Redbook CD audio has sample rate of 44.1 kilo samples per second. There should be no content above the noise floor above 44.1/2= 22.05_kHz, else that content would mirror about that 22.05_kHz frequency in an ugly sounding manner. Because of that most everything above 20_kHz is filtered out (its ultrasonic anyways, above the range of very good youthful hearing) and there is nothing above the noise floor above 22.05_kHz.
Two samples provide perfect definition of frequency, and ten samples provide very good description of phase. So 44.1_ksps is adequate to perfectly describe frequency up to 22.05_kHz, and provides very good description of phase up to 4.41_kHz.
"High Resolution" digital audio has higher sample rate, and tends to include more ultrasonic content above the range of normal youthful hearing. 96_ksps in the ideal would allow content to 48_kHz, but practicable filters reduce that by 10%-20% without damaging the audible portion of the spectrum. Good definition of phase is provided to 9.6_kHz, ten samples.
A problem is that many amplifiers are not as well controlled at higher frequencies, creating more nonlinear distortion products on that higher frequency input content, and those nonlinear distortion products can cause intermodulations in the audible range.
There can be benefit to limiting frequency of the input signal entering the amplifier. Redbook CD audio does that. Higher sample rate PCM digital audio limits it at higher frequencies, but too high for some amplifiers.
Be careful what you ask for.