pacman829 wrote:Anything above 48khz is beyond the average person's hearing range, and not perceptible to most human beings , as stated by the nyquist theorem
Uh... this is not what the Nyquist Theorem states.
Lets start with the range of normal human hearing, which is generally conceded to start rolling off at about 18KHz, and for most people goes off the cliff at about 20KHz. That is related to the distribution of sensory hairs inside the inner ear (cochlea).
The Nyquist Theorem is a principle of Sampling Theory, which states, in simple terms, that any wavetrain can be reconstructed if it is sampled at a minimum rate of 2x the frequency of the highest resident
harmonic.
Harmonic content stems from Fourier Transform - the sampling strategy relies on a summed-wave-construction model based on the mathematical premise that any complex waveform is a summation of a fundamental single-frequency sine wave and the odd and even harmonics that best-fits the original. For example, "tone" at 1 KHz is a pure single-frequency sine wave that would need only to be sampled at 2KHz in order to satisfy Nyquist. However, a square wave at 1KHz contains odd harmonics largely significant out to the fifth, but if you wanted to be exhaustive, there are a few per cent at the 7th. In practice, this means that the Nyquist threshold for a 1 KHz
square wave is actually about 14KHz, for an exceptional degree of precision.
For engineering purposes, the rule of thumb is to go for 2x 20KHz plus something, and the original music/CD sampling rate of 44.1 was born. It is obviously still in use, but one has to realize that it is limited in its
bandwidth, and therefore, low-pass filtering must be applied to any input waveform sampled at that rate -- the defect otherwise introduced is called "aliasing". This also applies to sampling video, or any continuous wavetrain.
48KHz has been the standard sampling frequency for video production since CCIR601 and
serial digital interface, because it works with all frame rates.
96KHz is overkill for stereo, but has some advantages in HD. Bit depth is another topic.
JP Owens, B.Sc.E.E