|Advanced Audio Recording|
Comparison between 48kHz,96kHz,192kHz and 384kHz sample frequency
In recent years higher samplerates like 96kHz and more are used for modern audio recording. This article shows some technical background, why this is the case. Please also read the article: Do we need 96kHz ?
The advantage of higher sampling frequencies
From the theory the current 48kHz frequency seems to be sufficient since it can represent up to 24kHz which is the half of the sample rate and meets the so called nyquist's critaria. Using an appropriate reconstruction filter, all frequencies below this border might be correctly restored. Practically this required an ideal anti aliasing filter which does not exist and cannot be constructed neither in analog nor in digital domains. This leads to the conclusion that some headroom is necessary to reduce the amount of frequencies close to nyquist's frequency to avoid the negative impact of mirror frequencies. Please see this article of the comparison 48kHz/96kHz for details and a general discussion.
Here I like to extend the comparison to 384kHz which is currently the highest known frequency for audio signal represenation. To understand the impact on the sound quality a closer look at the filtering techniques is usefull.
In digital domain, filters are often realized by FIR filters which strongly vary in complexity and size and therefore demand more or less calculation power. The subsequent image shows 4 different versions of audio filters (high cut) and their edge frequency:
As the image shows, the ripple in the stop band and the deviation in the pass band as well as the steepne it self depend on the number of the TAPs of the used filter. The more TAPs the more precission can be expected from the filter. Also a higher sample rate requires a larger number of TAPs already.
With a higher frequency and increased number of TAPs relativly more number of dots are available to define the ideal filter curve given by the theoratical equations. The more "dots" the higher the precision.
Higher frequencies make it possible to operate with different edge frequencies and though obtain a better separation of the stop band and the pass band the same time.
|© 2004 J.S.|