15 USB/SPDIF converters shootout

[DanRubin]

Dan:

 

I disagree. Most DACs (at least the ones I like) do not sound better from their SPDIF input at all, regardless of the SPDIF source. I also feel it is quite difficult to make an SPDIF input perform well. Take a look at the jitter measurements made by John Atkinson (stereophile.com) on DACs. Most DACs he has tested recently show better performance (less jitter) from their USB inputs.

 

<snip>

 

Once again, I totally disagree. Most of the good DACs around these days perform better via their USB inputs. But, certainly some manufacturers have not yet made the effort to have a really good internal USB interface, perhaps those are the DACs with which you are more familiar. I do think that there are plenty of people using external USB-SPDIF converters who are actually getting worse performance (but preferring the resulting sound in a flawed sytem) than if they were using the internal USB interface within their DAC. Generally speaking, excellent USB performance is available using the XMOS processor in a good implementation, and some folks do their own proprietary USB interface as well. Their is also a very good pre-built USB interface board available to OEMs from ABC-PCB in Switzerland which uses XMOS, any DAC manufacturer could use this board to get excellent USB performance, and the board can be taken to even higher levels of performance through external clocking.

I suspect that many of the people who prefer using an external converter are actually prerring the sound of higher jitter levels...

Barrows, you have been a steady and stubborn voice here for the superiority of USB. I'm confident you have heard far more USB DACs than I have and I respect your experience and technical chops. Yet most of what I read suggests a different conclusion. It's all anecdotal of course, but I'm not sure I can recall a single instance where someone said the USB input on a commercial DAC was not equaled or bettered by using a good external USB to S/PDIF converter. Add to that the rapid growth of the USB converter product category. If what you say is true, these products should start fading quickly and pretty much die out since they are a transitional product no one will need once enough legacy DACs are replaced by modern designs with good USB inputs. Let's see how that plays out.

 

You may well be correct about people preferring a high jitter sound, an interesting notion.

[dallasjustice]

I do think that there are plenty of people using external USB-SPDIF converters who are actually getting worse performance (but preferring the resulting sound in a flawed sytem) than if they were using the internal USB interface within their DAC. Generally speaking, excellent USB performance is available using the XMOS processor in a good implementation, and some folks do their own proprietary USB interface as well. Their is also a very good pre-built USB interface board available to OEMs from ABC-PCB in Switzerland which uses XMOS, any DAC manufacturer could use this board to get excellent USB performance, and the board can be taken to even higher levels of performance through external clocking.

I suspect that many of the people who prefer using an external converter are actually prerring the sound of higher jitter levels...

Barrows, I understand where you come from here. I appreciate you talking about how a design choice may affect an entire system. If you are assuming the system is a 2 channel system with the kind of engineering found in a Berkeley USB inside this hypothetical DAC, I get what you are saying.

 

However, very few actually have this setup. What about multi-channel? What about systems that can better deal with room modes at very low frequencies using multi-sub configuration and complex cross-over and delays? Simply using a single usb DAC ain't gonna cut it in all systems. The more complex multi-channel systems would likely require some type of muti-channel digital outs like a Lynx card. Maybe that's not an acceptable compromise for you. Sure, there are some decent muti-channel DACs available, but maybe those DACs compromise too much for others.

 

My point is that your assertions about what others are doing with their systems is just speculation. I would personally like to see more external digital converters with great features like cross-over, delay and properly dithered volume control to multi-channel outs. Everything matters, right? Btw, I still haven't found a flawless system. Have you found it? :-)

[barrows]

DJ: I am not sure what Lynx soundcards and external USB-SPDIF converters have to do with each other? Certainly, my comments here refer to two channel systems, MC opens a thousand cans of worms which I am not interested in dealing with.

As far as room correction, EQ, and bass management goes, for those who are interested in experimenting with those things, I would suggest that at least the first two are best handled by a computer, with high processing power rather than in hardware onboard a converter box, but again I am not sure what these things have to do with the discussion at hand, perhaps I am just being a little dense?

I prefer simple systems, complex systems require too much money, and always seem to have too many gremlins for me to deal with, I would usually rather spend my time listening to music than trying to tweak a super complex system to get it right, this is not to suggest that such systems do not have advantages, sometimes, but there are a lot of inherent problems, and places for more things to go wrong when one starts messing with active crossovers, bass management, and things like that. Although I am willing to deal with a couple of well placed, crossed, and EQed subs running from the amplifier outputs.

Flawless system, no such thing, I would also say there is no such thing as a virtually flawless sytem, not even close. But I will suggest, to get on topic, that there are virtually flawless USB interfaces in some DACs. I would also suggest that there are some DACs which are virtually flawless. The big flaws in home audio reproduction lie in the speakers, the microphones, the recordings, and sometimes the room.

[Elberoth]

If what you say is true, these products should start fading quickly and pretty much die out since they are a transitional product no one will need once enough legacy DACs are replaced by modern designs with good USB inputs.

 

That is probably how it is gonna look like, although an open question remains, how fast it is gonna happen. If you take into account, that most (if not all) modern DAC do not have USB inputs that would approach the level of sophistication and engineering of the Berkeley Alpha USB (and those DACs will still be with us in 5 years time), I would guestimate, that the outboard USB/SPDIF converters will be still with us in 5-10 years time, although their importance will certainly be smaller.

[Elberoth]

barrows +1

ar-t +1

 

Thank you for your contribution to this thread.

[jimbones]

For me this issue is not the DAC, it is the source end. I have a Windows laptop and I do not get good performance (actually horrible/unuseable) from my USB out. I HAVE to use a USB to SPDIF converter. Just ordered the Cuinas can wait to get/hear it.

[barrows]

For me this issue is not the DAC, it is the source end. I have a Windows laptop and I do not get good performance (actually horrible/unuseable) from my USB out. I HAVE to use a USB to SPDIF converter. Just ordered the Cuinas can wait to get/hear it.

 

Jim: I am unclear as to what you are saying, some more specifics might be helpful: are you saying that you love your DAC as is, and it does not have a USB input (or maybe it has a USB input which you know to be inferior)? And/or are you saying that your Windoz laptop is a poor computer source? In any case, I would like to add another approach into the discussion, network playback. The Sonore Rendu is available with SPDIF output, this is a network audio player, which renders the serving computer (or NAS) a non factor in sound quality picture. The Rendu (or similar network player, if there is one?) and a good SPDIF cable will result in great computer audio from DACs which require SPDIF input, without having to hassle with dedicated servers, CAPS, Jplay, or other computer system tweaks, as the tweaking is already done inside the Rendu (since it is a dedicated audiophile device built for music playback only).

[barrows]

I thought I would add some technical facts here which might elucidate why I am in favor of internal USB-I2S solutions in theory.

 

SPDIF receivers add jitter, this is a fact, how much one might add? Well the popular Crystek 8416 is specified to add ~200 pS. The much better Wolfson 8804 part is ~60 pS or so. Now consider that there has to be an SPDIF transmitter on the on the other end of the line, with similar jitter, so we are really talking about ~400 pS to ~100 pS of added jitter just to use SPDIF, and also remeber these are specified numbers, assuming a perfect cable, and perfect implementation.

Now, of course there are some very sophisticated, very expensive DACs out there, that use proprietary methods for SPDIF reception (like dCS, EMM, etc) and these DACs may be able to improve on these numbers. Many manufacturers resort to using an asynchronous sample rate converter to reduce the jitter-this works great for reducing measured jitter, but unfortunately this approach just turns the jitter into other sonic artifacts. Anyone who has access to a PS Perfectwave DAC can test the effects of asynchronous sample rate conversion themselves, just listen in "native" mode versus upsampling mode, and one will hear the damage done by the ASRC.

 

Now, a well implemented internal asynchronous USB interface will have jitter at basically the intrinsic jitter levels of the clocks; with good clocks and power supplies, this means single digit pS levels, with, perhaps a few more pS thrown in for error caused by imperfect transmission. Remember, even the best USB-SPDIF converter starts out with this same level of jitter, and then adds the jitter caused by the SPDIF interface itself. So, in theory, this is why an internal USB-I2S interface is inherently superior.

 

Here are some measurements of the Off Ramp with turbo clocks and battery power supply:

 

Empirical Audio Off-Ramp 4 USB format converter Measurements | Stereophile.com

 

These show quite a bit of jitter. It can also be illuminating to look at the jitter measurements John Atkinson has done of DACs comparing jitter spectrum of the USB input vs thta of the USB input. Most perform better through the USB input.

[jimbones]

Jim: I am unclear as to what you are saying, some more specifics might be helpful: are you saying that you love your DAC as is, and it does not have a USB input (or maybe it has a USB input which you know to be inferior)? And/or are you saying that your Windoz laptop is a poor computer source? In any case, I would like to add another approach into the discussion, network playback. The Sonore Rendu is available with SPDIF output, this is a network audio player, which renders the serving computer (or NAS) a non factor in sound quality picture. The Rendu (or similar network player, if there is one?) and a good SPDIF cable will result in great computer audio from DACs which require SPDIF input, without having to hassle with dedicated servers, CAPS, Jplay, or other computer system tweaks, as the tweaking is already done inside the Rendu (since it is a dedicated audiophile device built for music playback only).

 

I am saying that my laptop is a poor source. I tried using the USB out and I got all kinds of noise and "skipping". When I use and adapter to spdif it sounds very good (M2Tech) but I am upgrading to the J Kenny Cuinas. I expect it in 2 weeks. I like my Burson 160D although I would entertain upgrading that as well someday soon.

[jerryct]

1. True 75 ohm BNC connections are far superior to using RCA, but, the line has to be properly terminated and designed to maintain as close to 75 ohm impedance as possible, this is not trivial, and there will always be some degree of impedance mismatch (and hence some reflections), but no one should ever use RCA connectors for SPDIF.

 

Can anyone explain why the so called "pro audio" hardware all have rca spdif connectors. I am looking for mic preamps and have yet not found any with bnc connectors. The only bnc connectors are for word clock in and out. Is it because this is only the consumer version and the standard dictates a rca connector? I have only seen BNC SPDIF in the home/consumer audio world.

 

jerry

[junker]

Can anyone explain why the so called "pro audio" hardware all have rca spdif connectors. I am looking for mic preamps and have yet not found any with bnc connectors.

 

Digital "mic preamps"?? I'd assume most mic preamps are analog XLR.

[acousticsguru]

Digital "mic preamps"?? I'd assume most mic preamps are analog XLR.

 

Agree. Pro gear with RCA microphone S/PDIF inputs? Analogue guitar jacks maybe.

 

On a side note, reflections/mirror imaging are crucial in clocking, some would argue even more so, hence the standardized BNC (or 100Ω symmetrical) connections there.

 

Greetings from Switzerland, David.

[jerryct]

Agree. Pro gear with RCA microphone S/PDIF inputs? Analogue guitar jacks maybe.

 

Maybe i was not very clear. I mean AD converters with mic preamps which have SPDIF outputs. Like this

 

Lavry Engineering

 

"The AD11 includes built-in microphone preamplifiers..."

"The USB output is available in parallel with both XLR and RCA AES/SPDIF digital audio outputs..."

 

or this

 

ULN-2

 

Forget about mic preamps. But pro gears which can output digital only have RCA digital audio outputs. Why?

 

jerry

[junker]

You'd have to ask Lavry. I'm sure he'll have a lot to say about it...

 

I believe both units you posted have an AES/XLR digital out which is probably the best possible.

 

Generally I'd rank SPDIF cables in this descending order:

 

 

1. AES/XLR
   
2. BNC
   
3. RCA
   
4. Optical
   

[acousticsguru]

Agree. Pro gear with RCA microphone S/PDIF inputs? Analogue guitar jacks maybe.

 

On a side note, reflections/mirror imaging are crucial in clocking, some would argue even more so, hence the standardized BNC (or 100Ω symmetrical) connections there.

 

Greetings from Switzerland, David.

 

Seeing my Owen typo: meant 110 Ohms for AES/EBU, of course.

 

Greetings from Switzerland, David.

[acousticsguru]

You'd have to ask Lavry. I'm sure he'll have a lot to say about it...

 

I believe both units you posted have an AES/XLR digital out which is probably the best possible.

 

Generally I'd rank SPDIF cables in this descending order:

 

 

1. AES/XLR
   
2. BNC
   
3. RCA
   
4. Optical
   

 

Although I agree in principle, and this certainly true for e.g. the dCS converters I use, there is plenty of gear out there in which 110 Ohm AES/EBU isn't correctly (or not carefully enough) implemented, in which case 75 Ohm BNC may sound better. Even the contrary may occasionally be the case: I remember a friend's CEC transport which sounded best with a symmetrical to RCA (!) adapter cable (admittedly, impedance mismatching is more common in audiophile gear...). Surely best to try and give each unit and connection/termination a listen.

 

Greetings from Switzerland, David.

[acousticsguru]

Seeing my Owen typo: meant 110 Ohms for AES/EBU, of course.

 

Greetings from Switzerland, David.

 

Ha! Now I get it: those aren't always "my" typos! Modern technology... NOW Where does one turn off auto-spelling on an iPad, LOL...

 

Greetings from Switzerland, David.

[barrows]

Pro gear is made to very tight budgets in most cases. Cheap pcb mount RCA jacks (less than 1 dollar a pair BOM cost) are plentiful, 75 ohm BNCs are more expensive. Do not fall into the false assumption that pro gear must be made right! Note all the high feedback opamps, cheap SMPS, and relatively low quality construction on most (yes there are exceptions) pro gear in comparison to the best audiophile stuff.

There is no argument to be made in favor of RCA jacks for SPDIF transmission, they are inferior to proper 75 ohm BNCs and that is all there is to it.

[cchang]

Audiobyte Hydra: High-End USB interface | One man's journey into audio world

 

looks like an intresting new converter for reasonable price..quality clocks, battery powered aswell external usb.cannot find Much comparitions though.

 

 

Have used this DDC to pair the same family DAC (Rockna Wavequest)for a while, very satisfy with the sonic beauty it brings. Best result is achieved vis I2S over hdmi output.

[RichardHolbrook]

Has anyone tried the Human Audio Tabla converter?

 

Tabla - USB Interface for HD Audio - Human Audio

 

Interested in particular as to comparisions between the Tabla and the Berkley Audio USB converter.

[acousticsguru]

There is no argument to be made in favor of RCA jacks for SPDIF transmission, they are inferior to proper 75 ohm BNCs and that is all there is to it.

 

Right. But then it seems that was the consensus all along.

 

Greetings from Switzerland, David.

[Miska]

SPDIF receivers add jitter, this is a fact, how much one might add? Well the popular Crystek 8416 is specified to add ~200 pS. The much better Wolfson 8804 part is ~60 pS or so.

 

No, the Crystal CS8416 is not specified to "add" 200 ps (not pico-Siemens ) of jitter. It is quoted as typical value at output with typical transmitter. Or more specifically "typically leaked amount".

 

If you provide it with better input, it gives better output. I have made a lot of measurements with lot of different interfaces. USB is not systematically better, it is very easy to spoil things at the I2S side. 5 cm of wire is enough in many cases.

 

At least I've been able to get CS8416 + CS4398 combo to perform better than some "async USB DACs". Certainly way below 200 ps.

[barrows]

No, the Crystal CS8416 is not specified to "add" 200 ps (not pico-Siemens ) of jitter. It is quoted as typical value at output with typical transmitter. Or more specifically "typically leaked amount".

 

If you provide it with better input, it gives better output. I have made a lot of measurements with lot of different interfaces. USB is not systematically better, it is very easy to spoil things at the I2S side. 5 cm of wire is enough in many cases.

 

At least I've been able to get CS8416 + CS4398 combo to perform better than some "async USB DACs". Certainly way below 200 ps.

 

Miska: The choice here is between a USB-SPDIF converter, and a built in USB receiver in the DAC. No matter what one does, adding an SPDIF conversion step to an existing USB interface is going to add jitter, it is as simple as that. I know that you understand this. It does not make sense to compare a really, really good SPDIF interface to poorly implemented USB interface, as that would be apples to oranges. My point is strictly that given good implementation, a DAC with an internal USB interface will outperform the same DAC using an external USB-SPDIF converter at the same level of implementation.

I am sure many audiophiles have DACs with poor USB inputs, which will benefit from a USB-SPDIF converter at the level of the Berkeley Alpha USB, but that is not my point.

[Miska]

I am sure many audiophiles have DACs with poor USB inputs, which will benefit from a USB-SPDIF converter at the level of the Berkeley Alpha USB, but that is not my point.

 

But it was my point. Plus that the S/PDIF receiver itself rarely adds any jitter, but it may fail to remove some, since it's just a low-pass filter for a jitter anyway.

 

So most of the time, S/PDIF receiver doesn't have any jitter itself, but the circuitry surrounding it may have, as well as the I2S connection between the receiver and DAC may have the same faults as async USB implementations.

 

IMO, USB is just a bit better than S/PDIF. Firewire is already technically better than USB, although unfortunately fading out. Ethernet and especially PCIe (Thunderbolt) are much better.

 

I could even call design of USB standard "stupid", if HDMI wouldn't be worse...

[magnum innominandum]

It is quite excellent to have so many highly experienced and opinionated experts here.

 

I would like to pose a little contest to all of you experts. I have some purely hypothetical practical implementations of SPDIF outputs. Of course, it could be, they are based on real devices, who knows, right?

 

I should like to describe these in some degree of detail, covering physical layout and circuit.

 

The SPDIF outputs shall be connected to one of the following:

 

One DAC is fitted with the CS841X or AKM receiver (pick your favourite) and a direct (no transformer) input. The other is fitted with an equal input but a Wolfson Micro WM880X receiver. Neither employs secondary PLL's, Asynchronous Sample Rate Converters etc. and they shall be known from here as CS-DAC and WM-DAC. DAC Chip may be anything without ASRC build in.

 

We may presume source is a PC (that includes Mac, Linux, Android etc.) with the usual contamination of ground with possibly very high common mode voltages (as much as 1/2 of mains voltage) etc.

 

And I should like your expert opinions which of these entirely hypothetical SPDIF output arrangements coupled with which equally hypothetical DAC will produce the lowest measured jitter and which (if different) will sound best, looking at or listening to the analogue output of a given DAC...

 

So far the challenge, now the implementations:

 

Design 1:

 

Five parallel inverters (unbuffered) operating from 3.3V and driven by the sixth inverter drive a coupling cap (X7R SMD 0603 format 100nF) and a resistive divider of 330 Ohm & 91 Ohm. The voltage divider drives a SPDIF transformer without shield. Around 2 inch of wires twisted loosely together link the signal after the transformer to a 75 Ohm BNC Socket.

 

Design 2:

 

An unbuffered inverter operating from 3.3V drives an SPDIF transformer (actually same model as above) directly via a coupling cap (X7R SMD 0603 format 100nF). The resistive divider is placed after transformer. Around 2 inch of PCB traces link the resistive divider to a PCB Mount 75 Ohm BNC Socket. The traces are quite obviously not 75 Ohm striplines, an educated guess might consider them closer to 100 Ohm.

 

Design 3:

 

A TI Transmitter operating on 5V drives a transformer (similar design but different maker and model) via a coupling capacitor (100nF) and series resistor that produces 73 Ohm output impedance. The transformer connects to a PCB mounted 75 Ohm BNC connector with short traces.

 

Design 4:

 

Super Fast "popcorn logic" running at 4V implements a balanced drive to a transformer (similar to all earlier ones) with a parallel combination of NP0, X7R and electrolytic capacitor amounting to 100uF as DC blocker. The resistive divider is placed after the transformer and supplies 75 Ohm nominal (ensured by design) at better than +/- 3% and 0.7V P-P. All parts are SMD 0603. Additional RC "conjugates" are applied. The actual resistive divider and conjugates are placed directly below the output socket, which is RCA Type, for BNC an adapter is supplied. The applied conjugates are experimentally tuned using a TDR and a known 75 Ohm Cable, including the RCA socket and the RCA>BNC adapter.

 

So, please experts, riddle me this - who is best? Answers on a postcard or in this forum...

 

Magnum innominandum, signa stellarum nigrarum