Synchronous Reclocking Idea

[Nerull]

Alrighty. I have an idea about synchronous reclocking my DAC. Firstly, I use an AD1896 to asynchronously reclock (24.576 MHz) and feed that to a 74HC74 flip-flop for reclocking the s/pdif line in my cd player. Is it feasible if I connect the two using a coaxial cable (to prevent interference) or is that not a sound plan? If so, how would I go about doing so (making the two synchronous)?

Thanks!

~Tom

[A 8]

Perhaps you want to read that again and then think about how you can change it so that the lesser gifted of us can understand what it is you're trying to get to.

[Garbz]

The CDplayer's S/PDIF is being reclocked via a D-Type Flipflop circuit directly from the master clock and then fed directly to the back to reduce it's jitter.

The CDplayer's internal clock is sent to a separate jack on the back of the player.

Both S/PDIF and clock are then fed into the DAC. The S/PDIF to the receiver, the clock to the AD1896 to be resampled to the systemclock required by the DAC. Thus bypassing all the jitter induced in clock recovery.

http://www.tnt-audio.com/clinica/diginterf2_e.html Normal configuration + Clock circuit.

[igdrassil]

Yet another way to do it (and a better one, I admit) is to have a clock generator in a DAC module (somehere closer to reclock). Then you fed clock (through RS485 line or something speedy and balanced) into CD player.

In a pro audio equipment there is yet another modification of this technique. You can adapt both of yours DAC and CD transport to be a "master"-"slave" pair.
DAC is acting like a master device, providing clock for transport unit, as a CD transport (slave) has no internal generator.
Use two spdif lines - one from DAC to CD - clock one, and CD->DAC - data one.
Advantage of the "pro" technique - you can use pro- equipment with any of your transport or DAC. Yet another advantage - you may use any kind of frequency dividers/multipliers on the CD side because of good syncronous reclock on the DAC side.

I'm planning to use such way to connect external 24bit/96kHz DAC/ADC module to my Envy sound card. The only difference there will be no spdif - balanced ECL lines rulez forever.

PS: 74hc stuff sucks. Better use 74abt574 instead of 74hc74.

[Nerull]

Sorry! Garbz is correct. Must not have been thinking last night...

[rfbrw]

Originally posted by igdrassil

In a pro audio equipment there is yet another modification of this technique. You can adapt both of yours DAC and CD transport to be a "master"-"slave" pair.
DAC is acting like a master device, providing clock for transport unit, as a CD transport (slave) has no internal generator.
Use two spdif lines - one from DAC to CD - clock one, and CD->DAC - data one.
Advantage of the "pro" technique - you can use pro- equipment with any of your transport or DAC. Yet another advantage - you may use any kind of frequency dividers/multipliers on the CD side because of good syncronous reclock on the DAC side.

That is not quite correct. In the pro arena everything is slaved to a Sync Pulse Generator like the Isochrone OCX or Tektronix SPG600

[A 8]

[rfbrw]

[Garbz]

A 8 Incase you're lost we're talking about how to interconnect digital equipment without any loss of jitter. In consumer equipment this presents a great problem. In pro equipment there is a separate and dedicated clock external to all devices which everything else is synched to.

igdrassil your technique is the same as Nerull's only that the DAC is acting as the master instead of the CD. As long as the clock line is carefully transmitted it wouldn't make much of a difference to jitter characteristics would it? Afterall as mentioned by rfbrw in pro gear the clock is external to everything.

Also can you elaborate why the 74HC series does not make for a good reclocking device? Is it propegation delay or what? I know one is CMOS the otherone BiCMOS but what does this mean to the S/PDIF line?

[igdrassil]

External clocks are used in a studios.
I mentioned pro- (or prosumer if you like) devices as an example. They can be used as a master-slave pair. Or they both can be externally synched with clock clock generators.
Anyway, you can modify your digital source for a "slave" job adding spdif reciever and some clock dividing circuitry (to convert mck from spdif to a frequency you need in a CD player).
Also it is indeed better to place clock in a DAC module, near to reclock. In that case jitter of a cd->dac (data) and dac->cd (clock) lines are no matter to discuss.
When clock is on the CD side, jitter of the clock line became sufficient.