adamdea;579122 Wrote: > Quote: > Originally Posted by adamdea > ... > ... > > There seem to be 7 reductions before your signal becomes 7s and 8s. I > cant see any way of reducing the a 15, 0 starting pair to get either 8 > or 7- I wonder whether this is because the crossing point is the same > as the median value (7.5). If so I am now baffled as to how one > expresses silence in this 4 bit word.(pehaps you ignore 0, leaving 15 > values and a happy median of 8).] > .
OK - bear in mind what I said before, the mid-point is 7 (not 8, my mistake). silence = 7 = 0111 adamdea;579122 Wrote: > > ...As to where this takes us > > 1.1 You have pointed out that in information theory terms i have been > confusing two terms "precision" and "resolution". These seem to > correspond with 2 problems > a. the quantisation noise cuased by the limited choice of sample > values > b. the inabilty to produce a sound quieter than the lowest value > (apparently over or above the crossing value.) > > 1.2 It seems that an analog sytem has limited resolution but not > limited precision. If we return to your post 33, you described radio 3 > as 13 bit. > I assume that you meant that it had a snr of 78 dB. I have been making > the point at various stages (although apparently without using the > correct terminology) that whilst a digital recoding may have 16 bit > resolution and 16 bit precision, analogue systems can have 13 bit > resolution and unlimited precision. OR have I got this wrong and was > the 13 bit radio limited in both resoltuion and precision? > . 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. adamdea;579122 Wrote: > > 1.3 I am assuming that if a sound gets quieter it not only gets closer > to the noise floor but the quantisation noise relative to signal > increases. > . Correct. In an ADC. QN does not affect DAC's directly. adamdea;579122 Wrote: > > II. My major concern was over the example of the 24 bit DAC which has > "only" 17 bit resolution. I think this means it can only resolve a > sound 102dB below peak. I am however confused as to what this means > about its precision. I understand that the DAC doesn't have to guess at > the values it is decoding, but isn't the output the same as if it were > reading a 17 bit recording with 7 random numbers on the end . Does this > not mean that not only does the noise floor increase but the > quantisation noise will increase (or a noise equal to the level of > quantisation noise which would have appeared if the recording had been > at 17 bits?) > > Anyway thank you for your patience. 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 -- Phil Leigh You want to see the signal path BEFORE it gets onto a CD/vinyl...it ain't what you'd call minimal... Touch(wired/XP) - TACT 2.2X (Linear PSU) + Good Vibrations S/W - MF Triplethreat(Audiocom full mods) - Linn 5103 - Aktiv 5.1 system (6x LK140's, ESPEK/TRIKAN/KATAN/SEIZMIK 10.5), Pekin Tuner, Townsend Supertweeters, Blue Jeans Digital,Kimber Speaker & Chord Interconnect cables Kitchen Boom, Outdoors: SB Radio, Harmony One remote for everything. ------------------------------------------------------------------------ Phil Leigh's Profile: http://forums.slimdevices.com/member.php?userid=85 View this thread: http://forums.slimdevices.com/showthread.php?t=82050 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
