What's the dither all about?
The second analogy is a little cleaner (pun intended). Imagine that you have a bathtub full of bubble bath. The bubbles represent the upper 16-bits of your 24-bit audio information and tower above the underlying water which represents the lower 8-bits of your signal. However, in the lower water portion there resides some audio information. You agitate that water which causes that audio information to form into bubbles which raise up into the same level as the upper 16-bits. The new bubbles bring with them some of the water that was in the lower portion but join the upper echelon nonetheless. The agitation is analogous to adding dither noise. The bubbles that form bring with it some of the noise caused by the agitation but contain primarily audio information. When you convert to 16-bit, you simply cut (drain) out the lower 8-bit (the water) and the remaining 16-bits represent your final signal. This analogy works well because as you cut out the lower 8-bits of information the overall level of the bubbles lowers significantly which is analogous to the change in dynamic range between 24-bit and 16-bit. However, all the audio information is retained within the new dynamic range.
Glad to have cleaned up that controversy!
The result is smoother sounding... The ear can separate out the noise and hear only the audio signal.
So the question may remain as to why adding noise sounds better? In essence, when we add broadband
dither noise, it fills in the space between interval steps mentioned above. It has the effect of
spreading the many quantization errors across the audio spectrum. The result is smoother sounding -
the errors remain but are obscured by the dither noise. The ear can separate out the noise and hear
only the audio signal.
Copyright 2008 by James McCanna and licensed to Rain Recording. All rights reserved.
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