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My digital world: reclocking experiences


TheFlash

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Yes, analogue anoraks, look away now...

I had heard of the Innuos Phoenix but a Mutec MC-3+ USB reclocker came up for sale on the Wam. It was snapped up pretty sharpish but my interest was piqued, purely academic of course (must remember the dangers of that). The Phoenix handles USB in/out but the MC-3+ USB handles USB and SPDIF inputs (that USB suffix is because there is a cheaper non-USB vesion of the MC-3+). The one drawback of the Bluesound Node 2i, an otherwise stonking streamer IMHO, is its lack of USB out which means no matter how decent the DAC it feeds, the signal is clocked at the Node 2i end not the DAC end. A reclocker should make a better job of this than a mid-priced streamer... and then I read reviews raving about the Mutec magic in a range of higher end setups.

On eBay came up a pair of MC-3+ USB's with the PSU's ripped out and replacd by a short cable, ready for a linear PSU to power them. I bought them. Two? Why do you need two? Well some mad folk "cascade" them https://www.mutec-net.com/artikel.php?id=1388254422 - no, I don't get it either. Anyway I got the second one for close to 50% of the first as a bundle so why not. I bought an Allo Shanti LPSU which has two 5v outputs. Instead of Node 2i > Metrum Pavane DAC, you go Node > Mutec > Metrum - or in my case Node 2i > Mutec > Mutec > Metrum.  It's mad, clearly.

But it works. More detail, which I don't chase per se but here it gives more tightness, a shape to the notes. By definition reclocking must work across the spectrum but I particularly noticed the bass has a more obvious pluck or attack and things like vocals and guitar have more air around them. So they're staying.

These are a studio device which a hifi enthusiast noticed and the word spread. Studios use them to align the time signals on multiple digital devices, hence huge connectivity. You can use an external clock (like Mutec's own at c.£3,000 - crikey) or the MC-3+'s internal clock which is damned good. They have far more functionality than mere mortal music lovers require and what looks like a complicated set of lights, but I can assure you that configuration is dead straightforward, far easier than say on an equally ugly/functional RME ADI-2 DAC: just two buttons and a bit of toggling and you're done. The lights are extinguishable: pressing two buttons locks the panel and kills the lights, stopping someone in a studio or concert hall from accidentally ruining a performance...

Both photos show them powered up, with and without lights on. These are now tucked away behind my cabinet.
 
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Calling @This boy can wait. Are you receiving!

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External clocks definitely work. I use myself, which is battery powered for very low noise and with the Crystek CCHD-957 femto clock.

As you say, I noticed increased resolution and information retrieval.

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3 minutes ago, Heckyman said:

Nice write up, thanks.

Now you need to stack audiophile switches ;-) 

Now there is something where stacking can only take away not add! (FYI, I use a BT Gigabit switch but let's not stray too far from clocking...)

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‘The one drawback of the Bluesound Node 2i, an otherwise stonking streamer IMHO, is its lack of USB out which means no matter how decent the DAC it feeds, the signal is clocked at the Node 2i end not the DAC end‘

I think you may have misunderstood, dacs always have a clock before the chip.

Keith

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13 minutes ago, PuritéAudio said:

‘The one drawback of the Bluesound Node 2i, an otherwise stonking streamer IMHO, is its lack of USB out which means no matter how decent the DAC it feeds, the signal is clocked at the Node 2i end not the DAC end‘

I think you may have misunderstood, dacs always have a clock before the chip.

Keith

No they don't Keith. Not all of them or always.

They do if it's USB input, but many DACs do not use an internal clock when fed by an SPDIF source. Some rely on the SPDIF clock signal. It depends on the DAC.

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Do you have a specific example?

Keith

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SPDIF/AES carries both the clock and audio signal. ESS chips reclock internally, many do not. USB is asychronous and requires an internal clock. Before USB came on the scene, I believe the vast majority of DACs used the SPDIF clock. That's the whole basis of SPDIF.

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That is correct but not what I asked.

Keith

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Naim: "Since 1991 when the first Naim CD player – the CDS – was launched, Naim’s design philosophy has been that for best sonic performance from digital audio the master clock must be positioned close to the DAC chips. When the clock and DAC chips are closely coupled, timing errors are minimised. Whereas if a CD player is connected to an external DAC via S/PDIF, the master clock is in the CD player and the DAC chips are in the DAC, ie they are separated by the S/PDIF interface."

Plenty of threads on your favourite other forum suggest similar: "A lot of pro equipment has the option of using the S/PDIF stream for clocking to maintain synchronization across multiple devices (e.g. recorders). But most will buffer it, or have the option to buffer it, to clean it up a bit especially if synchronization is not critical. For consumer systems, with almost zero research, again some do and some don't."

More detailed, Norman Tracy: "Popular S/PDIF receiver chips like the Yamaha YM3623B and Crystal CS8412 are NOT crystal controlled but rather recover the necessary clock from internal Phase Locked Loops (PLL) locked onto the incoming data stream. The simple two pin can crystals often seen directly attached to '3623's and '8412's are optional. The 3623 uses the crystal clock to quickly lock onto the S/PDIF signal. The 8412 uses the crystal clock to determine and display the sample rate and jitter level of the S/PDIF signal. Both parts ignore the local crystal clock once locked onto the S/PDIF signal. Better (i.e. more expensive) outboard DACs use additional tighter PLLs after the receiver chip to further cleanup the clock. Generally there is a trade off between low jitter PLL and wide locking such that low jitter PLLs may result in a DAC being unable or slow to lock onto a high jitter S/PDIF input requiring use of a low jitter Class 1 source as defined in the 'Red Book' spec. from Sony/Philips. This lack of universality and the fact that parts budget spent on low jitter PLLs (like individual crystals for each sample rate) reduces the parts budget for everything else (like filters, DACs, analog circuits, power supplies, and case) leads many designers to leave well enough alone and use the clock straight out of the receiver chip investing the saved resources elsewhere in the design or lowering the cost. This allows the DACs master clock to be strictly a function of the source and interface. A few companies which make both transports and external DACs have implemented schemes in which the S/PDIF signal is supplemented with a second line carrying the master clock back from the external DAC to the transport. In this way the DAC's crystal becomes the master rather than the transport and the problems of recovering a spectrally pure clock are eliminated. No standards for this type of implementation exist. In reference #4 Dr. Hawksford calls for the clock signal to be transmitted on a second S/PDIF line, I know of no actual product which implements this scheme. Sony (in one product) and Arcam send the actual clock, Linn argues this leads to RFI problems and so they send a DC servo voltage which controls a VCOX in the transport.

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From 1991 fancy.

Keith

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I thought you were good at measuring, so please note that 'from' is not the same as 'since'. The ASR quote is from a month ago, incidentally. As you like to quote ASR, we have to assume it may be considered valid.

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Incidentally, I assume you are aware that even when using an internal clock, with an SPDIF input, the clock signal in the SPDIF is still used to regulate the internal clock in the DAC. It has to.

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Please.. so does Flash’s Node use a 1991 chip, that doesn’t reclock?

Keith

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