What is the difference between Linear Quantization and Non-linear Quantization?

Question

What is the difference between Linear Quantization and Non-linear Quantization ? I'm talking with regard to PCM samples. http://www.blurtit.com/q927781.html has an article about it but I'm looking for a more elaborate answer.

Answer 1

It's pretty simple really. With linear quantization every increment in the sampled value corresponds to a fixed size analogue increment. E.g. an 8 bit A-D or D-A with a 0 - 1 V analogue range has 1 / 256 = 3.9 mV per bit, regardless of the actual signal amplitude.

With non-linear quantization you normally have some sort of logarithmic encoding (e.g. µ-Law or A-law), so that the increment for small sample values is much smaller than the increment for large sample values. Ideally the step size should be roughly proportional to the sample size. This translates to a fixed S/N ratio (due to quantization noise), regardless of the signal amplitude. Another way of looking at this is that you can use fewer bits to get a given S/N ratio over the signal amplitude range of interest.