Phil Leigh;579158 Wrote: > OK - bear in mind what I said before, the mid-point is 7 (not 8, my > mistake). > > silence = 7 = 0111 > > > > In the UK, BBC FM radio in the late 60's through the 70's actually used > a 13-bit digital system to relay the signal between transmitters. The > sound quality in peoples homes was judged to be superb, despite the > 13-bit digital link. > > > Precision and resolution are two ways of looking at the same thing. > More bits = greater precision (less quanitization error) and greater > resolution (better SNR and DR). Resolution in this context simply means > the range between the loudest sound and the quietest sound that can be > captured. The number of bits determines this. > > > Anyway, analogue systems do not have infinite anything. That is a myth. > They clearly have limited resolution (SNR and DR). We could debate the > term "precision" in an analogue context. > > Information theory tells us what is required to accurately sample an > analogue signal. > > > Correct. In an ADC. QN does not affect DAC's directly. > > > > What is meant by "resolution" here is really confusing. > > A 24-bit DAC (all 24-bit DAC's) can only really reproduce "21-bits" of > analogue signal AT BEST because the bottom 3 bits of both the ADC and > DAC are measuring signals that are so tiny they are buried by thermal > component noise > (nothing to do with QN!). > > > The digital part of the DAC has 24-bit resolution. The analogue side of > the DAC has a "resolution" defined by the quietest sound you can hear > that is not noise. This has almost nothing to do with the digital side > and is largely governed by the componentry and circuit design of the > analogue side of the ADC+DAC - including the power supply > arrangements. > > Better, more expensive ADC+DAC's have less noise and can "resolve" up > to 21-bits. > > What does this mean in practice? > 1) Lots of tests indicate that no-one can hear anything beyond the 19th > bit in normal circumstances... remember that even the 16th bit is > incredibly low level... (-96dB) > 2) This has no bearing whatsoever on anything other than "what is the > quietest non-noise signal that can be reproduced"? > 3) The DAC in the Touch is good but can be outperformed by external > DAC's
This is really helpful and clear. I follow all of this until we get to point number 2. I have been wondering how I could get to whether I understand what you mean by this. If we had recorded in 21 bit samples rather than 17 bit samples we would reduce quntisation noise at all levels- the quantisation error in your 4 bit example does not occur at the lowest volume level. The limited precision of the DAC will produce a greater error than with a higher precision DAC at all amplitude levels (although the error will be lower relative to that amplitude at higher levls than it is at lower levels). I see that the DAC can't itself produce quantisation noise becasue it doesn't quantise. But I keep thinking that this will be the case with a 24 bit dac with 21 bit or 17 bit resolution too ie that if their outputs were compared there would be an equivalent effect as though that error were being made in the ADC (albeit with dither) The DAC surely only has the same number of meaningful outputs as if the ADC had had 21 bit or 17 bit precision? I am trying to get my mind round how the limited "resolution" at the DAC output compares with a limited adc bit depth which is then converted into a 24 bit word (as I understand happens when redbook cds information is sent to a 24 bit DAC.) Presumably the 16 bit word has 8 arbitrary digits placed after it. Isn't the output of the DAC with 16 bit "resolution" feed 24 bit precision data going to be indistinguishable from the output of a 24 bit dac fed that upconverted data. Perhaps this could be illustrated by comparing 1 (imaginary) ADC with 24 bit resolution and the 24 bit dac DAC with 21 bit "resolution" 2 same ADC but DAC has only 20 bit "resolution" 3 now ADC also has only 20 bit resolution and DAC has 20 bit "resolution". 4 now ADC is 17 bit but result is upconverted to 24 bit and played through 24 bit DAC with 20 bit resolution.. -- adamdea ------------------------------------------------------------------------ adamdea's Profile: http://forums.slimdevices.com/member.php?userid=37603 View this thread: http://forums.slimdevices.com/showthread.php?t=82050 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
