seanadams;419572 Wrote: > Huh? No you couldn't. The whole point of the DAC being in word clock > mode is that the source is going to give you the bits at whatever rate > the _DAC_ is running. > > > > Well, actually I'd consider it optimal to not deal with s/pdif and word > clocking at all... this is what Transporter does by itself. > > > > I don't understand this at all. > > > > Driving the platter isn't the problem, and it doesn't work the way > people might imagine from their experience with turntables or tapes. In > a CD player, the clock drives the PCM output and this _pulls_ data from > the platter via a buffer. The distinction being that the mechanical > parts are NOT part of the timing path (as they are with analog media). > So it's not nearly as bad as a lot of people think - jitter is nothing > at all like wow/flutter - it happens on a time scale a billion times > smaller.
On the "word clock not matching" thing, I was thinking "sample rate converter" chip in-line. Then it doesn't matter too much if there's a mismatch - that was going to be the case anyhow if the word clock was not being used. So the thing about the 4 DACs is a patent owned by Wadia. It's in their 9xx series devices. What they teach is to have 4 DAC chips per differential half of a balanced signal - so that's 8 DAC chips per audio channel; a stereo pair has 16 DAC chips. The DAC chips are all connected at their current outputs, so the output current is 4x a single DAC chip and the I/V converter then has to take this into account - simple enough. Now the trick is that since there are 4 DAC chips in parallel, you don't fire off samples to all 4 of them at the same time, you fire off a sample to DAC0 at phase 0, then you fire off a sample to DAC1 at 90 degrees, etc. Of course you've already upsampled to at least a factor of 4 and dithered and...... to obtain 4 different output streams per channel. If you're really good I guess you even correlate the dither between + and - of a phase / channel so that the dithering is differentially rejected. Shoot, maybe that's a patent in its own right somewhere. Maybe Wadia has that one too. I'm just a hobbyist so I could make my own system like this and although strictly I'm not allowed to, the harm to the patent owner is nil - I'm not going to buy an audio system that expensive ever. Plus the barrier to entry is extremely high as one needs custom hardware (read: FPGAs) to duplicate something so complex. It would take hundreds of hours to duplicate the setup. (and guess who designs FPGAs for a living - :-) ) I don't know the patent number, if you search, you'll probably find it. Interesting stuff about the transport / clock source, I wondered if the output data was taken from a FIFO. So what the word clock to the Transporter is, is exactly the same thing except the DAC is external and the clock loop is a bit bigger. The key is, the jitter is held to nearly 0 and is not a function of S/PDIF or cables or the transport or.... (in this setup a $10 transport sounds the same as a $50,000 transport and anyone who tells you they can hear a difference is a liar - all the transport has to do is get the correct bits to the DAC; the DAC controls ALL of the jitter at the I output of the DAC chips). With a $2000 Transporter that delivers 96/24, I wouldn't want to be selling high end transports any more. I guess they'll always have a place, but I think in 20 years most of us will use our laptop with an external HDD to play our music from - well for the digital music anyhow. So Sean, please do tell if you can - what, if any, is the plan for a 192 kHz sample rate capable machine along the lines of the Transporter? Also - is there any plan for a "real" transport-only device that has no DACs inside? Probably very small market and it makes no sense for you to make such a beast but on the flip side, those with external DACS are paying a lot of cash for a lot of stuff they don't use. Cheers guys. I'm enjoying this. -- wayne325 ------------------------------------------------------------------------ wayne325's Profile: http://forums.slimdevices.com/member.php?userid=29916 View this thread: http://forums.slimdevices.com/showthread.php?t=62747 _______________________________________________ audiophiles mailing list audiophiles@lists.slimdevices.com http://lists.slimdevices.com/mailman/listinfo/audiophiles
