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In Reply to: RE: SPDIF vs. XLR posted by Thorsten on September 04, 2016 at 06:28:54
Thorsten wrote:
"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 110 Ohm characteristic impedance of an AES/EBU digital cable is actually such a wide-range specification that it almost seems arbitrary. The actual specification falls somewhere between a generous 110 ohm ± 20% (88-132 ohm) range. I've built several DIY AES/EBU digital cables albeit short-length 0.5m cables, with the only stipulation being a simple twisted pair with a very tight twist ratio along with cable resonance damping, and find the AES/EBU digital interface to be subjectively superior to any S/PDIF cable interface, regardless of lacking any hands-on measurements, IME.
A more meaningful caveat of an AES/EBU cable interface is the notion that a balanced interface is less sensitive if not insensitive to cable and connector quality vs. a single-ended rca interconnect cable interface. A typical pro audio balanced cable and pro audio XLR connector can present just as lackluster performance as a mediocre single-ended rca cable tends to present. It took a number of DIY experiments to discover the importance of using a true high-performance conductor and XLR connector in order to achieve a more than satisfactory presentation via an AES/EBU interface, IME.
Follow Ups:
Hi,
I suspect your DAC uses a Cirrus Logic or AKM SPDIF receiver. These work poorly with SPDIF signals as they are designed for direct interfacing to AES/EBU which has at least ten times the common SPDIF signal levels. Unless suitable active signal conditioning is added SPDIF with these devices is much worse than it has to be.
And yet are the most common SPDIF devices and usually using the pretty terrible datasheet application too, all the way down to the inappropriate (slow slope, low bandwidth) transformer models recommended in the app note.
These receivers practically need AES/EBU signal levels to trigger cleanly.
Also, 0.5m is still pretty short, depending upon your source's rise time and sample rate this may be short enough to avoid any of the transmission line issues that cause reflections and signal distortion.
Try it with 5m runs.
I find once the DAC is equipped with a decent internal clock and a memory buffer there is so little difference between SPDIF, AES/EBU and USB as long as they are all galvanically isolated, that I'd be hard pressed to say I hear any.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
The Sabre DAC chip features a built-in S/PDIF decoder with inherently low jitter. It's actually a primary reason why I chose a Sabre DAC, since I don't use the DAC for a typical USB application.
See link:
Hi,
> The Sabre DAC chip features a built-in S/PDIF decoder with
> inherently low jitter.
Nope, it doesn't.
It features an SPDIF decoder with absolutely no jitter rejection whatsoever (meaning it's output has nanoseconds of jitter) and follows it with an asynchronous sample rate converter that attempts to clean that mess up.
That is not quite the same as "low inherent jitter". Heck, it's a whole other ketle of fish.
Many of those who have experimented with the Sabre find it performs better if the ASRC is placed in bypass mode by making the Sabre's clock linked to the source, even if measured jitter increases, but especially if jitter levels can be kept as low as if employing the ASRC.
But what matters in the end is that you enjoy the music.
Ciao T
At 20 bits, you are on the verge of dynamic range covering fly-farts-at-20-feet to untolerable pain. Really, what more could we need?
Fair enough. I misinterpreted the information. My impression was that the built-in S/PDIF decoder of the DAC chip helps to provide beneficial jitter reduction. Nonetheless, the Sabre DAC design is said to involve effective jitter reduction circuitry/methods.
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