Why does SPDIF basically suck?

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2 hours ago, Ralf11 said:

does it matter what noise is Behind the Digital Curtain as long as you isolate it?

 

 

Only in Oz and a neighboring continent down under.

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8 minutes ago, jabbr said:

 

The market will sort that out and no doubt there is a role for all three. 

 

USB: is here to stay, particularly if we consider Lightning as a variant of USB -- In my view not the best technically going forward but will likely hold the mass market DAC space.

 

Wireless and bluetooth will hold a space as well (should have placed these on the above list)

 

Ethernet: my favorite for long term "best"

 

Thunderbolt: hmm ... gaining traction in the "pro" space, I see this taking over the prior "Firewire" segment? Maybe, we will see. Don't have enough personal experience to compare with Ethernet.

 

I still put my $$$ on a singlemode fiber SFP+ module for killing the price/quality comparison. Hands down at this point.

 

optical link from Apple TV3 ain't no single mode

 

 

 

I have a Thunderbolt interface that also does USB.  I suppose I must consider the Thunderbolt to be superior as the required cable costs the most. 

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3 minutes ago, sandyk said:

 

We shall see Dennis, we shall see ! 

 Perhaps on your side of the Equator it all gets sucked into a Clockwise Vortex ?

Yes I was just thinking the electron spin is reversed below the equator or something like that. 

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Red is SPDIF derived from HDMI.  Green is USB.  Both inputs to the same device.  Now I believe the issue is HDMI rather than SPDIF.  

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2 minutes ago, buonassi said:

 

I agree that USB is here to stay.  What are the chances that USB-C becomes the standard connection type on the rear of DACs and computers in the next couple years?  Supposedly, this is the attraction of USB-C:  smaller/reversible connection, 3.1 speeds, higher power, and it doesn't matter which way you plug it in.

Well first I think we need an actual agreed upon USB-C standard.  Which we actually do not have.  USB-C could have been great, and was bungled worse than a keystone cops skit. 

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Well here is a J-test signal comparing optical and toslink. 

 

Computer USB source feeding Musical Fidelity V-link spdif converter.  It has coax and toslink.  I measured both into the same gear only difference being a coax or toslink connection.   Here are a couple close in 128k FFTs of that. 

 

 

 

Here is the Vlink with the same gear vs an Audiophilleo SPDIF converter which is BNC connected coax otherwise all the same gear.  The Audiophilleo is in light blue or cyan.  Looks much the same except a bit of a spike 75 hz each side of the central tone.  That is about 115 db down from the main signal however.  In a wider view there are a few more of those.  I would think maybe the PLL of the SPDIF input on the DAC is the main determiner of these results.  Both converters are asynch USB and probably lower intrinsic jitter than the receiving PLL is capable of managing. 

 

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2 hours ago, Panelhead said:

  Is the top graph the toslink and the second test coax?

What mansr said. 

 

The top graph covers 11980 hz and 12020 hz.  

 

The second and third are showing 11,900 hz to 12,100 hz.  The top two are the same signals. 

The third one is a different pair of signals.  Toslink via V-link USB to SPDIF converter and coax via Audiophilleo converter.  Same DAC in all cases.  

 

The clock speed of the V-link relative to the Audiophilleo is different by about 60 ppm.  The V-link had the same clock rate with coax as with toslink which makes sense.  The same crystal would be generating the clock used by both connections.  

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13 hours ago, buonassi said:

So the J test is done using only one tone at 0 dbfs (or close to) and observing the effects on the rest of the spectrum.  Anyone else see the shortfall here besides me?  Even if a J test ran on a sweep, it would be better, but still wouldn't really be sufficient.  Music isn't just one perfectly oscillating sine wave.  And it's reasonable to assume that when the USB chip is presented data that doesn't repeat as nicely as an encoded sine wave, that jitter could increase substantially.

 

Or maybe I'm looking at this through the lens of a lay person, and these tests are really good proxies for real music.  But I haven't heard the any counter argument yet. 

 

 

 

 

Jitter or mis-timing results in noise of various types showing up in the output.  It might be sideband tones around each frequency or just a wide increase in the noise floor depending upon which type of jitter it is.  Because of how the digital format works, how FFTs work the quarter sample rate tone is very good to expose significant levels of jitter. 

 

As mansr said a few posts ago originally SPDIF recovered the clock on each clock transition.  This could cause this could cause various bit combinations to show up as noise around the music.  The actual full Jtest mixed a 689 hz square wave with a 11,025 hz tone.  The 689 hz tone was toggling just the least significant bit.  This would cause the maximum amount of data related jitter. This part of the test really doesn't fit with USB sourced digital.  So many call it a Jtest when they use a high level tone at 1/4th the sample rate.  It actually is not the original Jtest that was developed by Julian Dunn.  

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Only used Firewire on Windows machines, but I've found it has various low level noise issues many complain about with USB while asynch USB mostly avoids those.  If you've got older good DACs a good USB to SPDIF converter seems pretty good.  Apparently too many cheap DACs skimp on the USB connection. 

 

Of course using reasonably priced Prosumer recording devices with ASIO connected USB  is generally a really safe way to go for great price/performance ratio.  Main drawback is no remotes.  But an increasing number of such devices have remote control apps you can use via a phone to control playback.