Home Computer Audio Asylum

Music servers and other computer based digital audio technologies.

[ Follow Ups ] [ Post Followup ] Thread: [ Display  All  Email ] [ Computer Audio Asylum ]
[ Alert Moderator ]

Why expect heroic DAC engineering to overcome a flawed interface?

Like you said, S/PDIF is flawed by design. I can think of at least 3 major issues with it. Communication is simplex (unidirectional) without flow control and therefore the DAC must have a variable clock, and it must be synchronized to the clock reference provided by the transport using a PLL. Second, the data is self-clocked via Manchester encoding, which was never meant for transmission of a high quality clock signal. Finally, it's single ended, so there will be ground loops and greater susceptibility to EMI and RFI. Given this kind of interface, I think it's unreasonable to expect the DAC to be immune to differences between transports and digital cables. If the audio industry were to adopt an interface standard that avoids these three problems, then I would agree to blame the DAC if transport differences persist.

I2S only addresses one of these 3 flaws, by separating clock and data signals. It's still simplex and still single ended. Likewise, AES/EBU only addresses one of these 3 flaws. It's balanced, but it's still simplex and encodes the clock with the data. And Toslink provides galvanic isolation, but it's also simplex and encodes the clock with the data, not to mention that a lot of Toslink connections are low bandwidth. It seems like all of these transmission standards were created before the importance of clocking in digital audio was well understood. It's a mystery to me why they are still used in high end products.

I think it's best to locate the clocks in the DAC right next to the DAC chips, which requires flow control by the DAC and therefore duplex communications. I'm not aware of any audio specific digital interface standards which support that, so we're stuck with general purpose computer interfaces like Async USB, FireWire, and Ethernet. These have their own disadvantages. Async USB and FireWire include DC power and ground, so they aren't galvanically isolated. Ethernet over twisted pair gets the physical connection right, but requires too much processing to be a good digital transport to DAC connection.

Unfortunately, the only interfaces that tick all the boxes seem to be proprietary.

This post is made possible by the generous support of people like you and our sponsors:
  Michael Percy Audio  

Follow Ups Full Thread
Follow Ups
FAQ

Post a Message!

 Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Subject:
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.

[ Top Top of Page ] [ Contact Us ] [ Support/Wish List ] [ Copyright © 2024, Audio Asylum, all rights reserved ]
[ General ] [ Speakers ] [ Tubes ] [ Vinyl ] [ Digital ] [ Hi-Rez ] [ Video Asylum ] [ Cables ] [ Tweaks/DIY ] [ Music ] [ Films ]