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Minidsp U-DIO8 USB to AES Converter Review

amirm

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#1
This is a review and detailed measurements of the minidsp U-DIO8 8-channel USB to and from AES/EBU digital converter. It is kindly sent in by a member. The U-DIO8 costs US $325 from the company. It is a very cool device in that it lets you stream 8 channels of audio to multiple independent devices. Or capture data form them in reverse. There is also a S/PDIF version.

The box is small which is a bit of a drawback as they used a 25-pin DB connector with a thick dongle to get the inputs and outs:

Minidsp U-DIO8 USB to AES SPDIF Multichannel Converter Jitter Audio Reviews.jpg

The connectors feel a bit cheap and I had a hard time inserting and removing my XLR cables from them. Not a big deal though in operation.

You need a 5 volt input adapter which I did not get. So I tested it using my lab power supply.

Digital Audio Measurements
I have been struggling to get good template for measuring digital output devices and I think I have finally found it. I play the J-test signal (12 kHz @ 48 kHz sampling) and then capture its jitter thusly:

Minidsp U-DIO8 USB to AES SPDIF Converter Jitter Audio Measurements.png


The red curve is minidsp U-DIO8. Blue is the cheap little Topping D10 which in addition to being a DAC also acts as USB to S/PDIF converter. Finally in green (and barely visible) is the Audio Precision APx555 measuring itself using the same XLR cable as I used with minidsp.

Sadly the U-DIO8 has much more jitter components than topping. They are a regular pattern which means bleeding from digital signal into the AES clock.

To get a better handle of what we are talking about all up, here is the same thing but shown in time domain, i.e. amplitude instead of frequency:

Minidsp U-DIO8 USB to AES SPDIF Converter Jitter Ampltidue Audio Measurements.png


We see peak to peak jitter of about 800 picoseconds. From what I recall, 500 picoseconds is the worst you can have (for a sinusoidal) jitter to preserve 16 bits.

Audibly though, I doubt that you can hear this effect. I tried to test it but realized that the couple of DACs I used perform much better with USB than AES input. And that I have no assurance of their S/PDIF being the same as AES. So I am not posting it. As a reference though, the Matrix MQA DAC got a SINAD of 115 dB with minidsp DIO8 which is shy of its best performance. But again, this may just be due to AES input not being as good as USB, not because of minidsp.

Conclusions
The minidsap U-DIO8 is a very useful type of device. It doesn't cost a lot for its functionality if you are trying to build an 8-channel device (hoping that the clock is shared between all the outputs). It has higher jitter as it should be audibly I am not concerned about it. Get it because you need it, rather than wanting to brag about the purity of its interface.

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amirm

amirm

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Thread Starter #3
Thanks! This is something new. Pls show APX555 jitter spectrum separately or put it in foreground.
You can see it in the second graph.
 

Matias

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rajapruk

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#7
If you would connect the U-DIO8 AES3 outputs to a dac with good ASRC, then would this jitter produced by the U-DIO8 be removed again, so to speak?
It would be interesting to know if the Okto Dac8 Pro would handle this in a good way, receiving signal from a U-DIO8.
 

daftcombo

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#9
Thanks a lot for this review!
I'm very interested in how miniDSP devices measure, and that one is part of them.
 

pos

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#11
Nice to see this product review, thanks @amirm!

They also have a version with SPIDF outputs (with BNC connectors).
In any case spdif and AES are pretty similar and it should be possible to convert from one to another directly (as per Rane note for example) or using one on Canare or Neutrik 110ohm/75ohms adapters.

I am currently using this device (the spdif version) with SMSL M8 DACs and (of course) I cannot hear any specific problem, so I guess ESS' Ultra Jitter Removator (or whatever they call it :p) does its job...
 

Hayabusa

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#12
Nice to see this product review, thanks @amirm!

I am currently using this device (the spdif version) with SMSL M8 DACs and (of course) I cannot hear any specific problem, so I guess ESS' Ultra Jitter Removator (or whatever they call it :p) does its job...
It looks like the jitter introduced by the U-DIO8 is caused by a sample-rate converter inside bridging two clock domains.
If this is the case, no post jitter remover can recover from that, the jitter is already in the sample values and not in the timing itself.
Normally a digital in/digital out device would introduce no jitter if the same clocks are used.
 

pos

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#13
@Hayabusa, AFAIK there is an ASRC in the device (actually 4 stereo units), but they only operate on the inputs. When using the device as a USB to AES adapters you should not have any resampling anywhere.
 

daftcombo

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#15
I am currently using this device (the spdif version) with SMSL M8 DACs and (of course) I cannot hear any specific problem, so I guess ESS' Ultra Jitter Removator (or whatever they call it :p) does its job...
Hi,
Would a miniDSP openDRC-DI allow the same use?
 

ElNino

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#16
But USB->AES is what Amir has measured... So why is there jitter then?
The jitter is almost certainly because the XMOS implementation MiniDSP uses synthesizes the audio clock from the XMOS master clock, and doesn't do it particularly well. It's probably the same issue that other people have noted with the MiniDSP USBstreamer.
 

g29

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#17
...
It would be interesting to know if the Okto Dac8 Pro would handle this in a good way, receiving signal from a U-DIO8.
Why would one pair the UDIO-8 with the DAC8 Pro ? Seems kind of redundant since the DAC8 PRO already has a USB input.
 

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