adamdea;579176 Wrote: > 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 an equivalent effect will > apply 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 the ADC had limited precision (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' > data 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" fed 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..
OK - I'll try. 1) Quantization error ALWAYS ONLY occurs in the lowest level - it is an error in the lowest bit - actually strictly speaking it's in the lowest half-bit(!) because 50% of the time the value chosen is correct... Let me put it another way. It doesn't matter what the sample value is, the error can only be +/- 1 bit. So the error in 12 vs 12.5 vs 13 is identical to the error in 1 vs 1.5. vs 2... You really need to be happy you understand this - as it is fundamental. 2) There's no concept of "LIMITED" PRECISION in a DAC. It has a precision, defined by how many bits it can handle. Period. You can argue its analogue side has a "resolution" defined as how high the noise floor is. 3) When redbook (16-bit) is converted to 24-bit, 8 bits of silence are added. Not 8 random bits. 4) in your 4 examples: 1: a true 24-bit ADC ( that doesn't exist) records music using all 24 bits. A 24-bit DAC will faithfully TRY and replay that. However if its analogue noise floor is effectively equivalent to 3 bits, you won't be able to hear anything but noise if you try and play a signal that only requires 3 bits or less of level. 2: exactly as per 1, except now signals using less than 4 bits are just noise 3: 4 bits of noise are recorded along with the music. A different 4 bits of noise appear at the analogue output of the DAC 4: The music is in the 17 bits (I'm assuming you are talking about an imaginary ADC with only 17 bits?). Converting this to 24-bit puts silence into the lowest 7 bits. Played back you hear 17 bits of music. Conclusions: 1) Stop reading Stereophile, it is just confusing you 2) If all of this still bothers you, just use an external DAC. You may not hear much difference. -- 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
