Antoine's system

[Antoine]

[align=left]

Up to a point, yes.  The potential for noise injection is pretty clear.  I'm not sure I buy the argument about inconsistencies in the timing of the clock generated by the USB host, especially in the case where the DAC (Devialet) is in asynchronous mode.  But I must add it's not something I've experimented with in any listening tests with so I'm only talking about what I would expect from a knowledge of how the hardware and software work.

Since Antoine said he's using the Mutec as a USB to AES/EBU converter, that doesn't say anything (I think) about whether there would be any sound quality improvement to be gained by re-clocking the USB.  Again...I might be missing something, that's just my --possibly naive -- reading of the story so far.

I too have trouble understanding what the added benefit of using HQ clocks is for the USB receiver itself. Intona writes it doesn't matter:

Ahem, this clocking thing on USB is an ambivalent issue that I recognize on many forums. All transceiver and hub chips have their own PLLs inside and they all rely on internal RC oscillators to derive the bit clock. We didn't see any change on eye diagrams of the USB bus whether the transceivers where clocked with +-500ps Jittter or +-5ps Jitter on our LeCroy SDA. Anyway, we took special attention to all design aspects and price economy was never a subject.

Everyone else bringing out audiophile level USB 'optimizers' writes it does matter or does incorporate HQ clocks local to the USB receiver/chipset. I honestly don't know if it does matter but it won't hurt either.

The re-clocking the Mutec does is done to the signal after the USB receiver, I guess the S/PDIF or AES3 signal since those have clock information embedded. Other USB optimizers "repacketize" so receive the packets on input and reconstruct those again for output. This way they "regenerate" the USB signal using a local clock. Their circuitry will also make sure impedance matching occurs and they frequently inject clean(ed up) 5V. The Intona does this as well but also provides full galvanic isolation.

This is what Mutec writes about it what it does for USB:

USB interfaces are the most commonly utilized devices for digital audio transmission in a computer-based music playback environment. But the convenience and ease of use often times come at a price of lackluster audio quality to the critical ears of high-end consumer audio aficionados and of professional users. It’s no secret that even the best D/A converters are not capable of reproducing and converting audio via USB at the highest possible level, which is why using digital audio inputs such as AES3 or S/P-DIF yields significantly better results and is generally preferred.

We have invested into our own research to uncover the underlying principles and the root of the problem with high-end audio via USB. In a nutshell, electromagnetic interference of any kind, but particularly those caused by audio computers and other IT devices, will induce noise and seriously disturb the audio transmission. In order to eliminate these disturbances and avoid their damaging effect on the conversion process as much as possible we have developed a new signal-isolating, asynchronous USB interface for the MC-3+ Smart Clock USB. It has been designed as a dedicated building block with a power supply that’s independent from the main board of the unit. In addition, the USB interface is galvanically isolated from the other parts of the circuitry and employs its own ultra-low noise audio oscillators that once again are autonomous and isolated from the other processes. In combination with IT-based high-speed isolators we have achieved exceptional reduction of the impact of noise interference within the USB data stream yielding a USB interface that’s virtually immune to any interference problems caused by PCs, laptops or music servers. At the same time, there are no limitations regarding the possible clock rates for playback from your music library with the MC-3+USB supporting all rates possible up to high-speed USB as well as DSD/DoP streams up to DSD/DoP256.

All of these features in combination with the subsequent re-clocking process, proprietary to MUTEC, leads to a significant acoustic improvement of connected digital audio devices that usually manifests itself in increased width of the sound stage, more precise imaging, and with a more musical representation of the recorded space and the instruments within it. Stock consumer audio devices, laptops, and audio computers can now achieve a new level of sonic perfection that was previously reserved for equipment with much higher price tags.

So to sum up it's benefits are:

- galvanically isolating the USB input from the rest of the circuitry to shut off electromagnetic interference from the source
- separate, isolated ultra-low noise audio oscillators for USB circuitry
- conversion to S/PDIF and AES3 and subsequent reclocking using a HQ clock

This may be one as well: pulling the USB circuitry from the DAC, to prevent electromagnetic interference inside the DAC. I've read Berkeley Audio Designs deliberately does not implment USB inside of their DAC's but as an external box because of this.