Comparing adaptive mode USB, Toslink and asynchronous USB

My Benchmark DAC 1 has 4 inputs: adaptive mode USB, Toslink, SPDIF and AES/EBU
My iMac has USB and Toslink.
I borrowed a Vlink192 from a friend so now I have an asynchronous USB converter with SPDIF (RCA) and AES/EBU out.

In JRiver I created 3 zones (Benchmark USB, Toslink, Vlink) and linked them.
Now they all play in sync.
All digital volume controls are disabled in JRiver so 100% for each output.
All zones set to WASAPI with the same buffer size.
All zones set to 24 bit and no re-sampling in DSP studio
Too the best of my knowledge no DSP is going on in any zone.

The toggle switch of the Benchmark allows for a rapid switching between the 4 inputs.
Listening was done using a Sennheiser HD600 headphone.

The adaptive mode USB of the Benchmark sounds good. Wide sound stage, dynamic.
The moment I switch to Toslink the individual instruments become more clear, less blurred compared with the adaptive mode USB. Obvious the resolution improves by resolving small details better. As a consequence the soundstage narrows and it sounds less dynamic.
One can also say the adaptive mode screams.
That’s the problem when comparing, there is an audible difference but the qualification is and will always remain a highly subjective judgment.

A likewise but smaller improvement is audible the moment I switch to the Vlink192.
I don’t hear any difference between the SPDIF (BNC cable with RCA adapter) and AES/EBU (110 ohm XLR terminated).
Using the Vlink192 yields a subtle improvement in sound quality.
As all zones send the same bits to the DAC this is probably due to a better jitter performance of the Vlink192.

amirm said:

Ah, I did not realize JRiver can play across multiple interfaces that way! .

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Just right click on a zone and choose Link http://thewelltemperedcomputer.com/SW/Players/MC14/MC_Zone.htm
Overview is also a nice screen, shows you wat is playing in each zone

Peter Breuninger said:

I'm surprised the Benchmark has adaptive USB. I though they were more cutting edge than that.

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This is a design from 2007 if I remember correctly.
At that time 24/96 was already pretty advanced.

We had to wait untill Ayre released the QB9 for async USB (2009?).
The last 2 years almost all new quality DACs feature async USB
Most of them use the XMOS receiver.

garylkoh said:

If you did not unplug the USB cable when switching to Toslink, it means that there is much more to it than just isolation.....

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I didn’t unplug.
I use a 2008 iMac.
I have heard that the jitter performance of the modern 3.5 V Toslink modules it pretty good.
So I do think it is the input jitter making the difference.

The Vlink192 claims to use galvanic isolation as well.

jkeny said:

Vincent, do these reports point to a noisy ground on the iMac and maybe a ground loop problem?

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To be honest I don’t see why this should be the case.
I did a very simple experiment.
Play over Toslink
Disconnect/connect the USB during playback. (thanks Gary, nice suggestion)
I don’t hear any difference.

What I can conjecture up is that in case of UAC1 over a full speed bus every 1ns a package arrives. This frame rate is probably not the most stable there is.
If this would be the case using Synchronous synchronization would work well
As it doesn’t this probably means the sample rate guesser has to adjust the speed of the clock every ns. If this result in an intrinsic jitter of 1 ns, it might be too high.

There is an interesting experiment by Jim Lesurf.
He measured the adaptive mode and the asynchronous mode by comparing a DAC Magic using its own USB input and when driven by a Halide (async)
The differences are remarkable


http://www.audiomisc.co.uk/Linux/Sound3/TimeForChange.html