Streamer output options

There were a couple of issues with early USB. It was not asynchronous, and early implementations of asynch were not universal. In addition, still recently, DAC vendors don’t always ensure the USB interface is galvanically isolated, which can cause digital and/or analog ground loops. The former increases jitter significantly, the latter adds hum. Especially bad when coming from a PC.

S/PDIF, while lower bandwidth, over optical suffered none of these issues.

Today USB is asynchronous and the highest possible bandwidth. Get an inexpensive USB isolator and you are good to go.

Another thing that’s happened relatively recently is that the clocks in DAC’s have gotten amazingly good (and cheap) compared to pre-2000 days. This means that the highest possible resolution of a clock is next to the DAC and therefore it should be in charge of the timing from upstream, which is what happens with USB asynchronous.

BTW, Ethernet is galvanically isolated by design, but not noise isolated due to coupling caps that may occur around transformer windings.

I'll reword your question a bit: 

 

Are the new implementations of usb now "as good as" AES/ spdif?

Yes- In the case of my streamer manufacturer.

According to Antipodes there was no USB driver option available that was as good as AES. It was only last year they achieved a USB strategy that equalled the sound quality of the other digital outputs and now they state the AES and USB outputs are more or less equal in sound quality. (clock considerations aside)

They offered upgrades to existing owners to update their units to the new hardware, as well as other updates, which is fantastic from a customer standpoint, but I have yet to do that- I am happy with my AES at the moment even though as others have stated it is limited to non-DSD 192/24 resolutions. All my Native DSD files are sitting dormant.

It is worth pointing out there are many excellent servers that do not have AES and use USB only- Melco, XACT, Aurender...

Per one cable manufacturer regarding history of digital cables: 

Before USB, there was Coaxial (S/PDIF) digital. This suffers from the technical problem that the clock must be recovered from the data stream, a technique that produces more jitter than desirable. Then came asynchronous USB, where the DAC controls the data rate, so a high-quality, low-jitter clock can be used in the DAC. This was technically a better solution, and it should sound perfect.

But it didn’t.

In fact, it sounded worse than using a Coaxial cable connection. Some blamed noise on the 5V line. Others blamed noise on the ground line. Various techniques were used (in an effort to offset the sound degradation), in the form of add-on boxes and dongles; galvanic isolation, regeneration, and noise filtering. These often gave some improvement but at a high cost; they also often left their own footprints on the music.

So, in 2018, we designed the original Black Magic USB cable.

We found the real problem is not noise on the ground or 5V lines—it’s noise that piggybacks on the data itself. Black Magic uses innovative techniques to reduce and absorb this noise, as well as special measures to prevent its radiation from the cable.

In 2022, we revised the whole cable, producing the USB ULTRA cable. This performs at an entirely new level from the original.

In 2023, we pulled out all the stops and produced the USB GOLD version. This uses selected silver/gold wire and a different kind of mechanical damping.

And in 2024, we have a new design: Prime – our best yet.

Implementation of interfaces needs to be taken on a case by case basis. How can anyone state categorically any single interface is the best. Usb optimization varies greatly across both streamers and dacs. I2S not offered on a great number of streamers so DDC's employed, optimization of this output varies with these, for dacs since this native signal path, less variability here except with quality of internal clock.

One would have to actually optimize and implement these interfaces in their own setups to determine superiority. I've tried any number of usb optimizations over the years, this with variety of streamers and dacs, with present setup I2S provides superior sound quality vs usb, this with both my Musetec DH-DA006 (sabre chip) and Laiv Harmony (R2R).  Musetec has one of the most sophisticated usb boards I've seen, Laiv middle of road.

15 to 20 years ago USB was not a great choice for audio but it has come a long way since then.