bhr1439;375769 Wrote: > I had read claims in Stereophile and (I think) The Absolute Sound that > music sourced from a hard drive sounds better than music sourced off a > CD player. I was skeptical of these claims, and am skeptical of my own > ears, which seems to confirm the fact. > > As soon as I started listening to music served by my new SB Duet > system, I detected a certain more lively and engaging aspect to the > music. I did an A/B comparison to assure myself levels are matched > (they are), and on close A/B listening, I cannot identify any > difference. Yet, the fact remains that my impression of music played > back via SB is more favorable, and this is not a subtle impression, it > is a definite emotional "wow". > > Here are the two different music paths: > > path A: Nakamichi MB-10 CD player digital out --> Tact 2.1S digital > processor --> Mark Levinson 360S DAC > > path B: Netgear ReadyNAS Duo --> SB Receiver digital output --> Tact > 2.1S digital processor --> Mark Levinson 360S DAC > > I cannot pin down any good reason why path B, with the Squeezebox, > should sound better. Both paths use the same, very high quality DAC. > Up to there, bits is bits, one would think. > > The audio mags claim music servers sound better because lack of jitter > on hard drive playback; that doesn't make sense for two reasons. First > the Levinson DAC has sophisticated dejitter circuitry, but more > fundamentally, the problem with jitter arises with the nature of clock > recovery from the S-PDIF waveform content. Both path A and path B use > S/PDIF digital signal to transfer the music data. > > The other potential reason is the effect of error correction on CD > playback. This would imply that the cheapie CD-ROM drive in my laptop > computer does a better job of reading music data (i.e., lower raw error > rate) than my CD player, giving rise to fewer uncorrectable errors > (uncorrectable errors cause the software to "fake it" by throwing the > data out and interpolating across the gap). > > Anybody know of comparisons in raw error rate in playback on CD player > vs playback on a computer CD-ROM drive? > > --Steve
Steve, When a normal redbook CD drive reads a disc it gets "one bite at the cherry" for each sector as the disc spins (yes I know there are a few that go beyond this but they are exceptional), whereas EAC or whatever take as many goes as they need to get the right bits from the disc without having to resort to any form of interpolation. However, I don't think this is the big difference...it is however what passes as the "science" behind the many treatments (cryogenic treatment of discs, mats, green pens etc) that claim to improve the readability of discs. This is despite the fact that a CD-ROM mech can reliably read 99.999% of discs without error! If these treatments are doing anything, I don't believe it is to do with "the bits" - I think it is that they may make it easier for the drive to read "the bits". Easier in this context means that the transport has to work less hard, the various servos and motors do less work and therefore... The above can easily be proven. None of the available commercial transport/disk treatments produce any difference in the bits ripped by a CD/DVD ROM mech via EAC etc. On the other hand, many people claim to hear improvements in replay quality from such treatments - why? I believe that the big difference is that the transport mechs of CD players inject electrical noise into the circuitry that then finds its way into the SPDIF stream or internal DAC and hinders the ability of the DAC to recover the clock with total accuracy (aka "transport-induced jitter"). This is a non-issue when ripping to hard disk as there is no D/A conversion, no clock and hence no TIJ. In summary: 1) looking at recovered bits is relatively pointless - the bits should always be perfect, either because they have been ripped with 100% accuracy or because the CD player is reading them in real-time with equivalent accuracy. The reality is that ripping has a slight advantage here in that the bits will ALWAYS be the same when read from the hard disk, whereas each time a CD player reads the disk it MAY get slightly different results. For hard disk replay, assuming an accurate rip, we should stop thinking about "the bits" in the same way that we don't worry about what our computers are doing with their "bits" - if something is wrong we will find out pretty quickly! 2) Differences in transport-related audio replay quality are not primarily connected to the bit-recovery process, but to the D/A process. With an external DAC connected via SPDIF, the SPDIF mechanism itself is susceptible to noise that interferes with the ability of the DAC to do its job. We can look at reducing this noise at source, or at making the DAC immune to the noise... or both. 3) Comparing hard disk replay to CD replay is in some ways about as far from comparing "eggs with eggs" as you can get. Up to the point where the SPDIF stream is sent (externally) or the bitstream is presented to the DAC (internally) the HD replay process is entirely deterministic and repeatable - just like a computer is. After those two points we enter the analogue domain and all bets are off!. CD replay has the added (random) complications of possible real-time read errors/corrections and transport-induced jitter... The only conceivable way that TIJ could exist in an SB-type product would be if the ethernet/wi-fi interface and/or the CPU generated "noise" that affected the DAC processing or the SPDIF signal generation... This noise could be directly induced or indirectly introduced via modulation of the supply lines... Jitter on the SPDIF stream can be dealt with to some extent by the downstream DAC circuitry. However, it would be better if this jitter was not there inthe first place. Unfortunately, SPDIF is inherently compromised in this respect and the termination/cabling etc means thats complete elimination of jitter entering an external DAC is almost certainly not possible. What we need is a better digital transport interface that doesn't embed the clock... If all transports were fitted with a clock-in and all DACS with a clock-out life would be so much easier! -- Phil Leigh You want to see the signal path BEFORE it gets onto a CD/vinyl...it ain't what you'd call minimal...SB3+Stontronics PSU - Altmann JISCO/UPCI - 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), Townsend Supertweeters, Kimber & Chord cables Outdoors: Boombox+Creative Sub (If I remember to turn it on...) ------------------------------------------------------------------------ Phil Leigh's Profile: http://forums.slimdevices.com/member.php?userid=85 View this thread: http://forums.slimdevices.com/showthread.php?t=57173 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/lists/listinfo/audiophiles
