adamdea wrote: > Noise level, Julf. Provided that the half lsb is spectrally flat by > dithering of otherwise the only effect of quantisation is to add an > error equivalent to spectrally-flat noise. This is quantisation 101. >
Modern audio ADCs (of sigma-delta design) generally noise shape the quantization error, in effect turning it into dither without adding any additional noise: http://www.ti.com/lit/an/slyt423/slyt423.pdf page 16: "Multi-order modulators shape the quantization noise to even higher frequencies than do the lower-order modulators." > > So the question is whether this noise will when added to the noise in > the signal pre-quantisation, produce a noticeable increase. > There is no such question that is relevant to the vast majority of audio DACs because they use Sigma-Delta technology to turn the quantization error signal into dither by shaping it in the time domain. > > Incidentally if anyone thinks I'm going off piste here I can quote from > a basic text > http://www.dspguide.com/ch3/1.htm > "First we will look at the effects of quantization. Any one sample in > the digitized signal can have a maximum error of ±? LSB (Least > Significant Bit, jargon for the distance between adjacent quantization > levels). Figure (d) shows the quantization error for this particular > example, found by subtracting (b) from (c), with the appropriate > conversions. In other words, the digital output (c), is equivalent to > the continuous input (b), plus a quantization error (d). An important > feature of this analysis is that the quantization error appears very > much like random noise. > The cited text does not seem to be updated to describe the vast majority of ADCs that are used in audio which are Sigma-Delta designs. This adds more complexity, and if included right up front might make an introductory text in DSP technology overly complex for newbies. If one measures real world gear on a test bench, this is what one typically finds. ------------------------------------------------------------------------ arnyk's Profile: http://forums.slimdevices.com/member.php?userid=64365 View this thread: http://forums.slimdevices.com/showthread.php?t=105717
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