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Bronze Member Username: Rick_rPost Number: 18 Registered: Mar-08 | Putting together a new hi-fi system and looking into more expensive ("good") CD players. I have a Sony DVD/CD player ($120?) that has a digital output that I've got plugged into my receiver which has a DAC. I'm assuming all the bits get read, error corrected, and sent down to the cable pretty much the way they got put on the disk (native CD sample rate and word size - 44.1 KHz?/24 bit?) My question is, prior to the DAC (in the receiver in this case), why would there be any variation in the sound quality of CD players. I can certainly see that the DAC and everything after the DAC would matter. But for fun, if I had say a Bryston BP-25-DAC pre-amp (DAC in the pre-amp), why wouldn't any old CD player with a digital output work the same? I saw a write up on the Bryston BCD-1 CD player in Hi-Fi+ magazine (issue 56 - Feb/08?) which has both analog and digital outputs. They talked some about 'hand selected crystals' and using the same clock to drive the transport and the DAC to reduce jitter. Say you had the BP-25-DAC, would you be better off using the BCD-1's DAC (analog from CD to preamp) or the BP-25's DAC (digital from CD to pre-amp). Perhaps a question for Bryston? More engineering stuff --- In theory (Nyquist critera), to get perfect 20KHz bandwidth signal, you only need discrete samples at 40KHz (2x base bandwidth) through a low pass filter. With digital, granted there's some quantization error in the samples, but at 24 bits, its gonna be pretty small if the ADC is doing its job. Assuming I can't hear above 20KHz and CDs sample at 44KHz, What's the bit with 96Khz oversampling and 192KHz up sampling?. Maybe this is getting too techy - but I'm curious about where the extra dollars play into the sound quality of the CD player and whether the digital interface allows the dollars to be spent in the pre-amp instead of the CD player. |
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Bronze Member Username: LamcamStanton, Ca Usa Post Number: 50 Registered: Nov-07 | I want to know too! |
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Bronze Member Username: Rick_rPost Number: 22 Registered: Mar-08 | I see there is a 'DAC and CD Transports' forum that might have been a better place to post this question. But looking around on my own, here's some info: From "The Absolute Sound" - March 2008 - Review of Esoteric G-ORb Rubidium Master Clock Generator has the sidebars "A Short History of Jitter" and "What Exactly is Jitter and Why does it Matter". Can't find a link yet (just out), but.... "Once an audio signal had been digitized, the conventional wisdom held, it was immune to degradation. If the bits were the same, the sound was the same. ... in the mid-1980's cirtical listeners reported hearing differences where none should have existed... It was an easy matter to prove the bit streams were identical ... with an October, 1991, AES paper title "Is the AES/IBU/SPDIF Interface Flawed?" by Malcom Hawksford and Chris Dunn... laid out in precise .. detail how the digital interface can introduce analog-like variablity in sound quality while preserving the bit-for bit accuracy... jitter is now accepted as a source of degradation in digital-audio recording and reproduction". "...in PCM encoded audio, an analog waveform is sampled at regular intervals (44,100 times per second in the case of CD) ... each snapshot is a 16 bit binary word that represents the analog waveform's amplitude ... If the clock controlling when the samples are converted to analog isn't a perfectly precise and stable frequency, ... timing error in the clock translates directly to an amplitude error in the reconstructed signal ... it turns out that the ear/brain is surprisingly sensitive to thse timing errors ... Keith Johnson... once told ... he could hear the difference between 8 and 15 picoseconds of clock jitter... The classic sonic signature of gitter is now well known and document: loss of space and depth; softening of the bass; hardening of timbre; a glassy sound on initial transients (most noticable on the leading edge of upper-register piano attacks); a metalic sheen overlaying the treble; and an overall flattening of the soundstage and homogenization of instrumental images within the stage... Jitter's deleterious effects aren't confined to D/A conversion, jitter in the A/D clock is just as sonically harmful... That's one reason why CDs remastered from analog tapes using modern A/D converts sound better." The product being reviewed is an atomic clock with a +/-0.05 parts per billion timing precision that can be used to provide a timing reference for the digital-to-analog conversion process. It can be used with Esoteric (and other) transports and processors that accept an external clock signal. Reviewer says he could really hear the difference - expanded the sounstage in all directions, instruments seemed to light up ... etc. And, it only costs $15,000. |
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Bronze Member Username: Rick_rPost Number: 23 Registered: Mar-08 | Perhaps, a more detailed reference on CD clock jitter: www.tnt-audio.com/clinica/jitter1_e.html This part 3 of a 5 part article, the references to the other pieces are hyperlinked at the end of each page. |