How can I tell if I need a better clock for my DAC?

is it safe to assume that the   manufacturer has dealt with this in making the one-box unit, making the transport section and DAC function together in a way that keeps jitter to a minimum?

Certainly not.  If this were the case, I would not have modded CD players for 10 years and got paid handsomely for that.  I don't mod anymore.

Steve N.

Empirical Audio

What you can do at home is listen.  If you hear a good track on another friends system that has superb focus, clarity and liveness and your system makes the vocalist 2 feet wide and the guitar 1 foot wide, then you have jitter.  If you hear echoes or "fill" between instruments in your system and not in your friends system, you have jitter.

There are standard jitter tests that display the spectrum of the jitter on the D/A output given a standard input signal from a disk.  If you were an engineer with the right equipment you could perform these measurements.

The problem is that even if you could, the results are not well correlated to listening tests.  I mean really bad jitter in the measurements is audible, but more subtle jitter can be just as audible and will not show up in the measurements.  This is the problem with the state of our measurement technology today.  May improve in the future though.

What you can do at home to improve jitter from your transport is:

1) treat the disks with Ultrabit platinum

2) spray-coat the top side on the disk with a rubber coating to reduce vibration - get this at Home Depot or Michaels etc.. Mask it properly with thin card stock.

3) re-write the disk on CDROM using DBpoweramp on PC or XLD on Mac - this improves the pit shape over the commercial disk

4) pay a modder to install a new clock and clock voltage regulator/power supply

#4 will make the biggest improvement in a CDP, but you will still benefit from 1-3 even with the modded clock.

Steve N.

Empirical Audio

Power delivery is the reason for high jitter from even good master clocks.  Power delivery includes:

1) power supply

2) cabling

3) decoupling caps

4) board design

5) regulator design

Steve N.

Empirical Audio

The Audio Alchemy DTI and DTI pro both use two or more CS8412 S/PDIF receiver as a PLL to reduce jitter.  The Pro is a lot better.   It will reduce jitter, but not like a good resampler such as the Synchro-Mesh.  Worth a try though.

Steve N.

Empirical Audio

There is jitter (lots of low level spurious signal at very specific tones).... probably inaudible but it is there.

This DAC has no reclocker, just an AK4113 receiver. It would benefit greatly from an external reclocker like the Synchro-Mesh if the S/PDIF input is used.  Are you certain that the j-test plot was using the S/PDIF input and not the USB input?

The Benchmark 3 on the other hand does a good job of rejecting jitter compared to prior models. Reclocker not necessary, however you are stuck with the sound of the master clock in the DAC. If you like that, nothing more to do.

Steve N.

Empirical Audio

The best way to keep jitter to a minimum is to see that your component has one of the high quality, high specification, clocks. If it doesn’t, sell it and buy one that has a great clock.

A good oscillator is a good start, however, there are a lot of other things that take that 80 Fsec and turn it into 200psec. These things include:

1) bad choices for logic family for the associated circuitry

2) poor board design, sliced-up ground-planes and crosstalk

3) Poor power delivery and decoupling caps choices and locations

4) slow reacting power supply and regulators

5) too much sharing of the power between oscillator and other circuits

6) no clever circuit design to minimize jitter

It turns out that these things are actually more important than having an oscillator with 80Fsec of jitter or one with 1psec of jitter.

there seems to be little doubt that the quality of the incoming digital signal (jitter, noise) will affect the amount of correction the DAC has to do and so affects SQ.

Yes, but it’s not correction, it’s simple D/A distortion.

It’s not so much the accuracy of the clock that is important, its the jitter and phase noise specs.

Steve N.

Empirical Audio

Yes, "a good oscillator (clock) is a good start". Without a good start, you have nowhere good to go. So what is this argument about?

The issue is implying that only a good oscillator is required. That's what the argument is about.  It purveys the wrong impression.

This is like saying that only a good D/A chip is required and you have the perfect DAC.  Not by a long shot.

Like most things, the devil is in the details.

Steve N.

Empirical Audio

Proper spdif connection between transport and dac should be made using 75ohm bnc.
rca is not true 75ohm and this can also introduce jitter.

George - You are dead right.  Just buying a 75 ohm cable with BNC's does not guarantee that the BNC connectors are 75 ohms either, particularly from Marketertek.  I have 75 ohms cables with 50 ohm BNC on the ends from Marketertek.

Also, BNC to RCA adapters should be 75 ohms as well.

Here are some cable jitter measurements, including some from Markertek:

http://www.audiocircle.com/index.php?topic=154425.0

Steve N.

Empirical Audio

The difference with BNC and RCA is BNC connectors are specifically designed to terminate to a particular coax cable and make a clean impedance transition.  This is why there are hundreds of types of 50 and 75 ohm BNC connectors.

Steve N.

Empirical Audio