evdplancke;686296 Wrote: > Thank you for the advice. If I understand you well, if those 3 > conditions are not perfectly met,you admit implicitly that some kind of > noise can be transmitted from the source to the DAC output. > > However these consideration seems to be based on the assumption that > the noise is coming from external sources (ground noise from cables and > power supply) and not from the signal path. But considering that a > digital signal is a perfectly square wave + noise, we should also > consider that some of the noise from the signal path can also be > transferred to DAC output. Sources of this "added" noise are typically > jitter, temperature noise and any kind of signal interference caused by > PSU, CPU processing,... > Even with signal reshaping, the return path for this noise should be > isolated from DAC output. In the same logic, I don't know how > optocouplers work, but do they produce perfect square waves at their > electrical output as well? if not, they would also transfer the noise > from the signal path, even if they provide perfect galvanic isolation. > > I don't want to raise polemic, but from my point of view, there are so > many unanswered questions about handling of the noise in the > reconstruction of the analog signal that I can not admit the "bit > perfect" argument alone to conclude that a digital source noise has no > impact on analog output noise. > > And if I remember well Phil, you are the only one on this forum that > objectivated by quantitative measurements that tt3.0 mods have an > incidence on DAC output signal (weither it is audible or not is another > topic).
Several points to cover here: 1) It's not exactly that the noise entering the DAC makes it through to the output - more that it can interfere with the correct operation of the DAC, resulting in an increase in distortion - which is what jitter does. 2) Yes the noise is coming in from external electrical sources - not sure what you mean by "the signal path" - there is no signal path INTO the Touch. It takes in IP packets which are just data and have NO noise inside them - they are simply pure data from the source music files. This is the great benefit of an IP-based streaming approach. Assuming data integrity - which is a computer thing and can be 100% verified (not an audio/hi-fi thing which can't!) there is nothing that can go wrong until we get inside the Touch itself. 3) The digital OUTPUT from the Touch is an "analogue" signal and can have embedded noise. This noise can get there from the outside sources I listed plus it can be generated within the Touch itself. This noise will be very low-level compared to the (s/pdif) "signal". However, the DAC has to handle/reject this noise properly otherwise it will interfere with the reconstruction of the analogue signal by messing up the clock recovery. This is ALL it can do - it doesn't affect the bits in the bitstream - that would be easily detectable and it does NOT happen. So this noise CAN cause jitter (and thus distortion) if not handled well by the DAC. If this is the signal noise you refer to, then yes it is embedded in the s/pdif signal and will pass through galvanic isolators Different DAC's handle this input noise differently. Some are better than others. So, if you follow my advice (and it's not just me, It's been said by many others too!) you will minimise noise ENTERING the Touch. To minimise noise generated inside the Touch from entering the DAC there are 2 strategies: 1) ignore it and let the DAC handle it 2) use a device to "clean" the s/pdif signal between Touch and DAC In all cases, ensuring galvanic isolation between Touch and DAC is important to prevent all your hard work being accidentally undone by providing an alternative route for noise to pass between the two devices. Finally - yes, I did measure a change in the analogue outputs of a Touch with the TT mods. Iwas surprised by the results but I do not doubt them. I can see a scientific explanation of how they MIGHT make this change. Theoretically they might also make a difference to the "signal noise" on the disgital outputs, but as I've explained, to what extent this is audible depends entirely on the design and execution of your DAC. regards Phil -- 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/W7)+Teddy Pardo PSU - Audiolense 3.3/2.0+INGUZ DRC - MF M1 DAC - Linn 5103 - full Aktiv 5.1 system (6x LK140's, ESPEK/TRIKAN/KATAN/SEIZMIK 10.5), Pekin Tuner, Townsend Supertweeters,VdH Toslink,Kimber 8TC Speaker & Chord Signature Plus Interconnect cables Stax4070+SRM7/II phones 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=91322 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
