reclocking

Alfe - you may need a better converter to beat the USB interface in that DAC. They do exist.

Steve N.
Empirical Audio

First, USB interfaces vary in their jitter. Some are better than others. You should not need a reclocker with a good async USB converter.

Second, no DAC can eliminate jitter. In fact most DACs that reclock with upsampling can actually add jitter compared to a low-jitter USB converter feeding a DAC with no upsampling.

Its all about the quality of the clock and reclocking circuitry. Its like buying a tonearm cardridge. You get what you pay for.

Steve N.
Empirical Audio

Based on the shootouts the best converters are:

1) Off- Ramp 5
2) Diverter HR
3) Berkeley Audio

Steve N.
Empirical Audio

Steve...where does jitter occur?

Jitter starts at the master clock in the transport or async USB interface. It then just gets worse as it passes through buffers, translators and cables. The DAC receiver may add more or reduce it a bit. The D/A chip generally adds more.

Is it more likely to come from the transport/music server or from the DAC?

Both have contributions. The worst will be the transport or device that contains the master clock.

Can it be eliminated completely and how would that be done?

Cannot be eliminated completely, but it can be reduced to the point where other system noise and distortion is more prevalent. This is not easy though. One must use very low noise fast-responding power supplies for the master clock and the associated circuitry. This results in tight voltage regulation. Likewise, the D/A chip must have very low noise fast-responding regulation on the supply voltages. DACs without upsampling and with good voltage regulation can delivery a very low jitter result. You generally get what you pay for here.

Alfe - the jitter solution is actually fixed with async USB, but it is highly dependent on the implementation. Most are poorly implemented. There are however other pitfalls that are more difficult to overcome, such as the effect of the playback software and audio stack. Most of these disappear when one uses a network-driven solution such as Sonos or SB, but hi-res is the limitation of these right now.

Cerrot - you continuously complain about the SQ of cheap USB converters and poor designs. This is like buying a cheap CD transport and concluding that all transports are garbage.

There are some high-end reviewers such as JA and Steven Stone that use USB converters for their digital references, and for good reason. They outperform everything else.

Steve N.
Empirical Audio

Alfe - you can see some Async USB and reclocker jitter plots here:

http://www.audiocircle.com/index.php?topic=115008.0

Any manufacturer that claims their device (not the clock) delivers 10psec of jitter on S/PDIF are not living on this planet.

Steve N.
Empirical Audio

Alfe - that is a shame. I dont believe that most mastering studios realize how important jitter is in the A/D. It is expensive to get low jitter in a A/D and the other devices used, like preamps are critical as well. Most studios dont spend enough for this equipment. This seems to be the trend; lower cost garage studios using computers etc..

Once the jitter is in the master, there is nothing you can do to improve this.

I'm a strong believer in capturing the master on analog tape and mixing it analog. Then digitize it.

At lest the playback jitter we can have an effect on. There seems to be no linits to getting it low enough. Evey time I achieve lower measured jitter, I can hear the improvement. Even the difference in sound quality between 50psec and 25psec. Who would have thought?

Steve N.
Empirical Audio

Cerrot - Almarg is correct. Packetization has no bearing on the jitter in networked or USB systems. Both are buffered and master clock established in the device interface.

The older Adaptive technology relied on the computer clock, so it was deficient is this way. IT could only be improved with local PLL's which are no match for a free-running clock.

Likewise, DACs that have master clocks that are synchronized to an incoming stream are no match for a free-running clock. Jitter will be higher.

Buffering of the data and "pull" protocol combined with a free-running master clock with low jitter is simply the best way to achieve the lowest jitter in digital. See these plots to realize how low it can be:

http://www.audiocircle.com/index.php?topic=116570.0

The plots at the bottom approach the lower limit of jitter using current affordable technology. Most of the jitter is in the 15-18 psec range. You will not find a transport this low.

Steve N.
Empirical Audio

Alfe - you may think that the heart of the digital system is the DAC, but it isn't. It IS the interface that contains the master clock. That can be a built-in USB interface, external USB interface or a device and reclocker.

The problem is that most USB DACs have poor implementations of USB interfaces. The fact that the power and ground of the DAC USB interface shares these resources with other DAC circuitry is bad. This is what makes an external USB converter with a good power supply far superior to the majority of built-in USB interfaces. Just read the reviews. Most of them say that the S/PDIF input performs better than the USB interface.

Steve N.
Empirical Audio

if you have Toslink output on your laptop, you could feed this to a reclocker like Synchro-Mesh and then S/PDIF to the DAC rather than USB. Reclocker is around $600 and a good S/PDIF cable $250. 30-day money back makes it a cheap thing to try.

Steve N.
Empirical Audio