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RE: SPDIF vs. XLR

Posted by Thorsten (M) on September 4, 2016 at 06:28:54

In Reply to: SPDIF vs. XLR posted by jllaudio on August 30, 2016 at 20:21:27:

Hi,

Unless the DAC rejects jitter very well (which means it has some form of variation on the genesis digital lense build in), all long cables will degrade signal quality and add jitter.

Given that where there are plugs and sockets mismatches are almost unavoidable, the cable system with the greatest mismatch at the plugs will usually do worst, presuming all other parts of the system (Source, actual cable, DAC's input) are correctly engineered (which in some cases is a big presumption).

If you compare the Canare "75 Ohm" RCA Plug and generic 75 Ohm BNC Plug, you will find one having around 55 Ohm CI and the other around 65 Ohm CI. Generic RCA Plugs come in at around 45 Ohm CI, as they were designed for 50 Ohm systems.

For AES-EBU the nominal impedance is 110 Ohm but XLR Plugs are more like 300 Ohm. Any of these is sufficient to create reflections, but XLR will be worst and BNC will be least bad.

The Cable also comes into this, especially at 5m length and 192kHz sample rate, where delays in the cable become material.

The precise nature of the SPDIF receiver is also important, some of these chips are designed for AES-EBU signal (up to ten time the signal level of SPDIF) and barely lock with SPDIF signals and as a result have much higher jitter than needed to be in practice and with SPDIF signals.

Ultimately non of these connections (RCA, BNC and XLR) are ideal and I recommend keeping SPDIF/AES-EBU connections as short as possible (preferred << 12").

My advise would be to extend the USB Cable run by using any of the various "USB Repeater" Gizmo's as extender. At a recent show I demonstrated this with a total of 12 generic 1.5m USB Cables daisychained using B->A adaptors and four iFi iPurifier 2.

Not only was it an > 18m run of USB, it used very generic cables and many adaptors and created a seriously bad condition. Even removing only one of the iPurifier 2 from the chain dropped the connection.

In practice I cannot say that I heard much if any difference with this massive kludge of USB Cabling (I cannot recommend using it like that of course) over just using 1pcs of the Cables, no adaptors and a single iPurifier 2 at the end of the 1.5m cable.

Incidentally, no need to use iFi's product, I am sure the alternatives out there can do the same job just as adequate. Put at the end the particular device you like the sound best with your DAC or USB-> SPD converter.

Thor

At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to intolerable pain. Really, what more could we need?

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