Saturday, November 08, 2008


Dither is an intentionally applied form of noise, used to randomize quantization error, thereby preventing large-scale patterns such as contouring that are more objectionable than uncorrelated noise. Dither is routinely used in processing of both digital audio and digital video data, and is often one of the last stages of audio production to compact disc.

Found this in a technical paper when I was doing some research on Dither.It gives us an idea how our brain uses the sense organs and distorts information.

Our brains are quite good at ignoring unimportant things. For example, you walk into someone's house and you smell a new smell - the way that house smells. After 5 minutes you don't smell it anymore. The smell hasn't gone away - your brain just ignores it when it realizes that it's a constant. The same is true of analog tape noise. If you're like most people you pay attention to the music, you stop hearing the noise after a couple of minutes. Your brain is able to do this all by itself because the noise is unrelated to the signal. It's a constant, unrelated sound that never changes with the music and is therefore unrelated - the brain decides that it doesn't change so it's not worth tracking. Distortion is something different. Distortion, like noise, is typically comprised entirely of unwanted material (I'm not talking about guitar distortion effects or the distortion of a vintage microphone here...). Unlike noise, however, distortion products modulate with the signal. Consequently the brain thinks that this is important material because it's trackable, and therefore you're always paying attention.

1 comment:

Samhita said...

cool comparison. two dollars here. buy whichever chacolate u like.

LSB quivers in most ADCs. Dithering increases the statistical moments close to realistic measurement of repetitive/predictable or patterns of limited spectrum; but it's not panacia. the model/distribution of LSB noise and the dither noise should be complementary. though LF applications use PSNR generators (+DAC) those can be subtraced in post processing, the high samplerate ADCs use built-in reverse biased diodes, a near perfect source of white noise.

Distortion- that's actually a trick used by ramya on me! she can mutter hours of apparently juicy stuff with no juice in it- end of the conversation i suddenly realize- she didn't convey anything. ur example falters here. it is not my brain which tracks the distortion induced by her, it is she, like a PLL who tracks my response. But her PLL is kind enough to stop the moment i seek back my existance.

(hope she is reading it ;-) )

back to serious talk- amplitude distortion is least dangerous compared to phase distortion / jitter/ timing errors in digital circuits. and even on analog audio.. the vertical distortion matters only when the logarithm scale there are spikes apart from the signal