bhr1439;377315 Wrote: > Hi, I'm the original poster on this thread. Thanks for the thoughtful > comments, everyone. > > First off, I appreciate Phil Leigh's insights; he pointed out two > potential mechanisms that could potentially generate an audible > difference, reminding me that that both paths start with the optical > disc. That is > > path A: optical disc --> Nakamachi CD player optical pickup subsystem > --> decoding and error correction (single pass)--> synchronous > bitstreams --> S/PDIF waveform encoding --> TacT 2.1S processor --> > Mark Levinson 360S DAC > > path B: optical disc --> computer CD-ROM drive optical pickup subystem > --> decoding and error correction (with optical drive retry, if needed) > --> harddrive --> S/PDIF waveform encoding --> TacT 2.1S processor --> > Mark Levinson 360S DAC > > Path B will likely generate the more accurate data, as it can retry > reading bad data, wheras it's typical for a CD player to "press on > regardless" and use tricks such as interpolation to bridge over known > bad data. Different data means different audio, and it's reasonable to > think that more accurate data will correspond to a more appealing aural > impression. > > As a previous poster suggested, recording and comparing S/PDIF data > should be able to confirm or reject the hypothesis path B data being a > more reliable representation of the music. What I would expect to see > is rock solid repeatability in the S/PDIF stream originating in the > server, and run-to-run variability in the datastream originating from > the CD player. Now, if only I had an S/PDIF recorder... > > Another point Phil makes is that path A has potential for a noisier > S/PDIF signal, due to EMI from the CD player's electromechanical > components. Noisier S/PDIF signal can result in increased jitter in > the recovered data clock, and increased DAC clock jitter is known to > make for a less pleasing aural experience. > > JezA strongly suggests that I try taking my TacT processor out of the > path and seeing if that makes a difference. That's a reasonable > troubleshooting experiment, and I will try that as opportunity permits. > I don't expect a difference, though. That's because I'm using the Tact > processor in digital-in / digital-out mode and there never is any D/A > conversion occurring inside the box. True, there is clock recovery > happening as part of the conversion from S/PDIF waveform back to > digital data stream for processing, but I do not expect that jitter is > affecting the integrity of the bit stream content (i.e., I do not > expect misclocking of data and changed data words -- this would be > HIGHLY audible as impulsive pops in the audio when it is converted to > analog downstream). Also, the Mark Levinson 360S employs a FIFO buffer > and locally generated clock that obviates the S/PDIF waveform (generated > at the output of the TacT) as a source of clock jitter. > > So, no smoking gun yet that confirms or refute my impression, but at > least there's a plausible (to me) hypothesis on what's going on. > > --Steve
Steve - as a small aside the high-quality ASRC chips in the TACT are indeed doing a D-A-D process internally in order to change the sample rate and bit depth in realtime to 24-bit/184kHz for the internal DRC process. You can find in-depth discussions of the mechanics and implications of these chips elsewhere (Google). This is basically where the jitter-sensitivity comes in; even though it seems to be an entirely digital process...it isn't. Changing the TACT PSU and using adequate 1.5m spdif cables (the length is important) all help. But this is off-topic. The issue I thought we were discussing can be restated as "Do transports sound different - and why could the SB transport be "better" than a CD mech?". The TACT is a red herring in this discussion!. -- 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
