Why does SPDIF basically suck?

[sandyk]

6 hours ago, Ralf11 said:

and does it suck for Redbook, or only for high bit rates?

 

 

 

 Coax SPDIF is fine up to it's typical limitation of 24/192.

With today's technology it is capable of being taken much further, but  most recent developments have been made in the area of USB audio, which has then facilitated the use of high res DSD that wouldn't have been otherwise possible.

 

Most members of the general public still wouldn't even know what DSD audio is though!!!

[jabbr]

2 hours ago, Fitzcaraldo215 said:

What could possibly be better than total control of the totally buffered d-a process by the DAC master clock?  Oh, wait.  Spdif/Toslink/AESEBU do not do that.  Asych USB does.  Hmmm.

 

No doubt one could treat SPDIF as an async clock, and do a proper clock domain crossing rather than reconstruct the clock at the receiver. No doubt one could reimplement the Toslink transceivers using high quality, low jitter optics. No doubt a new version could overcome the low bitrate limits. The real world, however, has moved on. More modern synchronous alternatives such as I2S via LVDS over HDMI haven't achieved market penetration and require specialized PCIe cards ... and still don't do DSD.

 

Realistically we have USB and Ethernet and Thunderbolt moving forward 

[Panelhead]

5 hours ago, sandyk said:

Well implemented Coax SPDIF can sound markedly better than most USB implementations , although it's bandwidth is inadequate for recent DSD implementations, where there is a limited amount of material available, and not in popular music either.

There is no reason why Coax SPDIF's bandwidth couldn't be markedly improved these days if there was a will to do so.

  There are 12G coax cables available now. All have BNC connectors. These will handle any audio signal used today. Cheap too compared to specialty audio coax cables. 

  The transmitters and receivers used in audio applications may not handle 12 GHz, the cable is not the problem.

[One and a half]

59 minutes ago, Ralf11 said:

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

 

 

After 6000 posts, you should know by now?

 

For the benefit of others, one needs to know the enemy in order to defeat it. Without precisely measuring noise and how much can affect DAC front ends, even methods of isolation can be defeated, since the conquest of noise is, so far, a blunderbuss approach instead of lasers. This is on top of transmitter receiver limitations in either S/PDIF or USB.

[One and a half]

38 minutes ago, jabbr said:

 

The real world, however, has moved on. More modern synchronous alternatives such as I2S via LVDS over HDMI haven't achieved market penetration and require specialized PCIe cards ... and still don't do DSD.

Audio interfaces have a such a poor method of standardisation, reminds me of the Fleetwood Mac song 'Go your own Way'. Was it Sonore that listed dozens of different methods of I2S over LVDS, apart from PSAUDIO which has a small following, everyone else is going their own way. 

[sandyk]

19 minutes ago, Panelhead said:

The transmitters and receivers used in audio applications may not handle 12 GHz, the cable is not the problem.

 

 Yes, I realise that.

[Ralf11]

1 hour ago, jabbr said:

...

Realistically we have USB and Ethernet and Thunderbolt moving forward 

 

which is best?

 

and how bad is the optical link in the Apple TV3?

 

[Pete-FIN]

3 hours ago, sandyk said:

 

The only way to get well implemented USB to outperform well implemented Coax SPDIF , is to remove the degrading influence of the PC's internal +5V SMPS, and replace it with clean low noise power via preferably an external battery derived +5V supply, which has no capacitive effects back to A.C. mains earth, and use a higher quality USB cable of the shortest possible length ,where there is vastly improved isolation between the D+ and D- leads and the incoming power leads.

 Well implemented Coax SPDIF assumes the use of the correct 75 ohms BNC plugs and sockets, as well as quality isolation transformers at both ends .

BTW, the best USB cable is NO USB cable, just a modified USB-A male to USB-A  female adaptor .

 It is also possible for USB memory sticks powered via a  clean external supply to work with a modified USB adaptor where +5V and screen are not connected through. This helps to remove possible earth loops with desktop PCs as the 0 volts and screen of USB memory sticks are internally connected together, and the PC's internal 0 volts is connected to mains earth.

 In this case I use a USB Regen, but I need to insert the USB memory stick into the Regen AFTER the adaptor is plugged in and the PSU is turned on , in order for the USB memory stick to be recognised by Windows 10.

 In the attached photo, the bottom cable is replaced by the adaptor.

 

Thanks for the answer. Nice to learn new things.

[jabbr]

10 minutes ago, Ralf11 said:

 

which is best?

 

and how bad is the optical link in the Apple TV3?

 

 

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

 

 

 

[esldude]

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.

[sandyk]

7 minutes ago, esldude said:

Only in Oz and a neighboring continent down under.

 

We shall see Dennis, we shall see ! 

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

[esldude]

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. 

[esldude]

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. 

[jabbr]

1 minute ago, esldude said:

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. 

Thunderbolt is basically PCIe on a wire — so if you have a PCIe card, easy to remote. 

[jabbr]

7 minutes ago, esldude said:

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

Maybe that’s why the Internet works differently there? Ethernet cables have the wrong chirality — but fiber? ?

 

Hmmm ... perhaps we could do balanced streaming where the (-) path goes in the Southern Hemisphere ... and do we need to listen in Ecuador?

[esldude]

 

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.  

[buonassi]

35 minutes ago, jabbr said:

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.

 

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.

[esldude]

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. 

[Ralf11]

so, the std. is too loose?

[Pete-FIN]

4 hours ago, buonassi said:

 

What are the chances that USB-C becomes the standard connection type on the rear of DACs and computers in the next couple years? 

 

I think it would be good to have USB-C at the back of the DACs. It seems like a well designed connector.

 

I also think that High-End Hi-Fi manufacturers should make it so that there are USB-B and USB-C ports at the back of "money is no object" DACs.

 

4 hours ago, esldude said:

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. 

 

Wait what!? I did not know that there is no 'universally agreed' standard for USB-C.

 

Can you please tell more about this, what is not agreed in USB-C?

[sandyk]

7 hours ago, One and a half said:

After 6000 posts, you should know by now?

 

 Surely > 6,000 posts in just over 18 months is a record for this forum ?

[mansr]

8 hours ago, jabbr said:

No doubt one could treat SPDIF as an async clock, and do a proper clock domain crossing rather than reconstruct the clock at the receiver.

No, you can't. You can do something more elaborate than the standard PLL and achieve much lower jitter, but you always must somehow avoid drift between your local clock and the incoming signal. USB does this by providing a feedback channel whereby the receiver can instruct the sender to slow down or speed up as needed to keep the fifo at a suitable fill level. S/PDIF is unidirectional, so nothing like this is possible there.

[mansr]

47 minutes ago, Pete-FIN said:

Wait what!? I did not know that there is no 'universally agreed' standard for USB-C.

 

Can you please tell more about this, what is not agreed in USB-C?

I'm curious about that too. The standard has gone through some updates, but to my knowledge all variants are compatible.

[jabbr]

28 minutes ago, mansr said:

No, you can't. You can do something more elaborate than the standard PLL and achieve much lower jitter, but you always must somehow avoid drift between your local clock and the incoming signal. USB does this by providing a feedback channel whereby the receiver can instruct the sender to slow down or speed up as needed to keep the fifo at a suitable fill level. S/PDIF is unidirectional, so nothing like this is possible there.

Of course it’s possible — every reasonable FIFO codes for the possibility of buffer over or under runs. Big enough buffer and should be statistically rare. 

[mansr]

1 minute ago, jabbr said:

Of course it’s possible — every reasonable FIFO codes for the possibility of buffer over or under runs. Big enough buffer and should be statistically rare. 

The S/PDIF spec requires a transmitter clock tolerance of ±1000 ppm for consumer devices. If your local clock is perfect, that worst case translates to a drift of 3.6 s per hour. To play a CD's worth of music without risk of underflow, you'd thus have to pre-buffer for about 4 s before starting playback. That might just about be acceptable. However, the DAC can't know upfront how long the incoming stream will last. For all it knows, you'll be playing continuously for a week. Handling that would require a 10-minute pre-buffer.

 

I suppose you could deliberately slow your local clock by 1000 ppm and avoid the need to pre-buffer. You'd still need a huge fifo to pick up the excess incoming data, of course, and eventually it would fill up.