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Review and Measurements of Allo DigiOne RPI S/PDIF

amirm

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#1
This is a review and detailed measurements of the Allo DigiOne Raspberry Pi digital audio (S/PDIF) interface. It retails for USD $99 and is on kind loan from Allo. Unlike its higher-end brother (DigiOne Signature), this is a single board implementation at half the price.
Allo Digione Raspberry Pi SPDIF Output Jitter Review.jpg

When combined with a Raspberry Pi, and a suitable "audio operating system" (e.g. Volumio used in this review), you have a $135 networked S/PDIF interface. Hook the output of this board to your favorite DAC and you automatically add networking to it, allowing you to place the computer server elsewhere and stream content to your audio system.

Testing digital audio outputs is quite different than our typical analog measurements. Here, we are interested in how pure the digital output is as to produce good performance out of any DAC regardless of how good its S/PDIF interface is. I took a shot at this when testing the Allo Digione Signature but I was not too happy with them as the results were rather hard to interpret. Here, I have taken a different shot at it, hopefully making it easier to understand. So let's get into it.

Measurements
Given the success of my analog measurements using a "dashboard" view, I created a similar performance dashboard. The stimulus signal is "j-test." The J-test is a square wave at 1/4 of sampling rate (12 kHz here since our sample rate is 48 kHz). In addition, the low order bit is toggled + and - one causing all the bits to flip at once (e.g. 9999 to 10000 and back). The toggling of all the bits is designed to aggravate/accentuate jitter over S/PDIF cable. Ideally, we would see no trace of it if the system is resilient to what content is being transmitted. In other words, the S/PDIF signal needs to be independent of the audio being played to perform its role as an ideal "digital transport."

To have a reference, I tested my Audio Precision APx555 in its loopback mode with its unbalanced (S/PDIF) digital interface:
Audio Precision APx555 Digital Unbalanced Loopback Jitter Measurement.png


Focusing on top right (FFT), we see the spectrum of noise and spurious tones going as far as 300+ kHz. We see a noise spectrum starting at 10 picoseconds at low frequencies and dropping. We have a few spikes above 30 kHz but their amplitude is exceptionally low at just 6 picoseconds.

The time domain (oscilloscope) view on the left reflects the same with the waveform seemingly being random with no distinct patterns (good).

RMS level of jitter is 73 picoseconds. Peak is highly variable and falls in 200 pico seconds or so.

A cool but odd feature of APx555 is to treat the digital stream as "audio" and perform classical measurements on it. Here, I am having it output THD+N equivalent in the form of SINAD in dB. As in analog audio, the higher, the better. Yes, 16 dB is not a lot but we are talking about digital sample recovery so it is fine.

Next, to get really calibrated, I thought I test the Topping D10 as a S/PDIF interface bridge from USB:
Topping D10 SPDIF Coax Jitter dashboard Measurement.png


Starting with FFT on top right, we immediately see the 250 Hz square wave in J-test becoming visible as jitter. 250 Hz is a square wave so when decomposed into frequencies, we see it and all of its odd haromonics (250, 750, 1250, etc). So we clearly have data dependency in the S/PDIF output of the Topping D10.

We see the same in scope display on the left where the sine wave pattern of the 250 Hz harmonics are clearly visible. The waveform does not look random as it did with APx555 output. RMS jitter has risen to 126 picoseconds and peak is nearly double at 400 ps. Jitter SINAD as dropped to 11 dB.

Now let's see how Digione does:

Allo Digione Raspberry Pi SPDIF Output Jitter Dashboard Measurement.png


We get an output that is darn near APx555. No sign of the 250 Hz harmonics as we saw in Topping D10. RMS jitter is 72 ps. SINAD is a dB or so lower at 14 (this value jumps around fair bit).

Scope display on top left shows a much more random sequence again which is good.

And here is the same measurements for Allo Digione Signature:
Allo Digione Signature Raspberry Pi SPDIF Output Jitter Dashboard Measurement.png


This is a tiny bit better. We are hitting the best case performance of Audio Precision APx555 here so not much more room to move. I lost those results but a higher resolution FFT showed the signature to have lower noise than non-signature DigiOne.

Conclusions
Allo is one of the few audio companies that has excellent engineering skills and importantly, verifies its designs using measurements. So it is no wonder that even the non-signature DigiOne produces such textbook performance (i.e. essential match to Audio Precision APx555). At $99 it is a bargain way to get networked S/PDIF functionality.

Given the willingness of Allo to participate in online audio communities, I can't find any faults with the company or the product.

Needless to say, I highly recommend the Allo DigiOne to build a networked digital audio interface for streaming applications.

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stunta

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#2
Thanks Amir. Given that Roon can stream to a Google Chromecast audio (CCA) device which is cheaper and has an optical out, any thoughts on how the Allo compares to the CCA?

Also, since rPi can act as a Roon endpoint, if it can detect the Allo as an output device, that would be neat.
 

miero

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#3
Nice :)
@amirm would you show also a classical frequency-vs-amplitude plot of J-test for some DAC please? (with visible 250Hz signal component if possible) I'd like to compare how that relates to the frequency-vs-level plot.

And a question. The instantaneus level in a scope plot is computed as a difference of a measured signal minus an expected signal?

Thanks.
 
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johan

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#4
A big thx to Amir. He is doing a great service to the audio community, to us all. About time that audio hardware is tested and I think that manufacturer will start paying more attention and test instead of using words like "femto second clock" and the likes..

Digione and Sig are very close in measurements to AP machine loopback (and thats a 20k USD machine..). Our engineering team has looked at the results and I seen smiles :)

Stunta , yes many customers use RPI+ Digione/Sig as Roon end points. (dietpi is a great choice as a OS/player)
 

miero

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#5
Also it would be nice to know if jitter changes with sampling frequency: 44100 vs 48000 and also 176400 vs 192000 (Hz).
 

johan

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#6
Also it would be nice to know if jitter changes with sampling frequency: 44100 vs 48000 and also 176400 vs 192000 (Hz).
Hi Miero

Digione and Sig use 2 NDK ultra low jitter (22/24Mhz) clocks with buffers. Theoretically there should be no difference
 

johan

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#8
Hi Miero

we measure jitter at the buffer (as oposed to spidif stream ) as our AP analizer does not have that particular capability . We have the waveform on our website

In addition Amir is stressing the system to accentuate jitter

"" In addition, the low order bit is toggled + and - one causing all the bits to flip at once (e.g. 9999 to 10000 and back). The toggling of all the bits is designed to aggravate/accentuate jitter over S/PDIF cable. Ideally, we would see no trace of it if the system is resilient to what content is being transmitted. In other words, the S/PDIF signal needs to be independent of the audio being played to perform its role as an ideal "digital transport ""
 
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amirm

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#9
Also it would be nice to know if jitter changes with sampling frequency: 44100 vs 48000 and also 176400 vs 192000 (Hz).
I changed the sample rate as such but didn't see a noticeable difference with sine wave. I don't have J-test signals for higher sample rates (my old Audio Precision could generated them on the fly but the new one does not so I have to use files I have).
 

amirm

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#10
@johan
How can I relate following statement from Allo website to amirm's measurements?
The jitter meter in APx555 can't go very low. I suspect the limit is what it measures in loopback (can't find it in the specs).
 

Jimster480

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#11
I changed the sample rate as such but didn't see a noticeable difference with sine wave. I don't have J-test signals for higher sample rates (my old Audio Precision could generated them on the fly but the new one does not so I have to use files I have).
Can't you use the old one to measure this then? Or the overall performance is just much worse in the sense that it wouldn't matter?
 

amirm

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#12
Can't you use the old one to measure this then? Or the overall performance is just much worse in the sense that it wouldn't matter?
The old one has even worse specs for its jitter measurement. And its FFT doesn't have a lot of resolution so other than generating the signal, it is not of much value otherwise.

Actually, in this context generating the signal would be of no good since the analyzer is not controlling this device. Neither one supports networked DACs.
 

Michael Kelly

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#14
Would you be willing to re-run our 502DAC digital test with the new method? Full disclosure to those who do not know, I am the designer and manufacturer of the 502DAC that Amir was kind enough to test previously. Thanks!
 

amirm

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#15
Would you be willing to re-run our 502DAC digital test with the new method? Full disclosure to those who do not know, I am the designer and manufacturer of the 502DAC that Amir was kind enough to test previously. Thanks!
Sure. Here you go:

Pi 2 Design 502DAC Jitter dashboard Measurement.png


The 250 Hz square wave is not nearly as pronounced as Topping D10 (good). Likewise, the 12 kHz square wave primary "tone" in J-Test is bleeding out but again, not nearly as much as it was in D10.
 
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#17
I liked the digione in my system. But recent comparison with Smsl DP3 used as streamer showed that DP3 is really better regarding sound quality than the digione (more details, larger soundstage). I'm curious of DP3 measurements as streamer (no dac used) for comparison.
 
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#19
Comparison has been done using RCA or BNC with RAC adapter for both.... with same cable and setting;
In addition usb on DP3 is also quite good but not relevant for that comparison.
 

johan

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#20
Hi Renan ,

Digione has been tested independently and shows jitter close close to AP machine as you can see above. Might be that system is sounding better for your ears in your particular system .

In any case , we welcome any comparison and testing . Enjoy your system .
 
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