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Review and Measurements of iFi iPurifier S/PDIF Digital Audio Filter

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amirm

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Maybe the Reference Forum could use a post with proper 16 and 24 bit J-Test WAV files...
Yes, we are both thinking of the same thing. Should make a collection and put them in a zip file like Bennetng did to make it easier to download. Let me work on that.
 

Blumlein 88

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I have the ones JA uses at Stereophile for 44/16 and 44/24 I have attached. They have the 230 hz LSB toggle included which really isn't needed except for SPDIF inputs.
 

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amirm

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I have the ones JA uses at Stereophile for 44/16 and 44/24 I have attached. They have the 230 hz LSB toggle included which really isn't needed except for SPDIF inputs.
Good deal as that matches the response of the 48 Khz one I posted:

upload_2017-12-29_17-30-59.png
 

Jakob1863

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I have the ones JA uses at Stereophile for 44/16 and 44/24 I have attached. They have the 230 hz LSB toggle included which really isn't needed except for SPDIF inputs.

As Julian Dunn choose/constructed the J-signal especially for the examination of possible jitter effects when using the AES/SPDIF interfaces that of course is the main goal; if it is useful in other circumstances depends.
But anyway, the term J-signal denotes this special constructed signal and using it in that way will hepl to prevent discussions about "real/official" and "not so real/official" J-signals.
Why should we call a pure sine wave of Fs/4 kHz a J-signal as it only leads to confusion?
 

Superdad

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Amir:
The photo of the product in your first post is not of the iPurifier S/PDIF device. It shows a device with a UBS 'B' plug. Perhaps you will want to correct that.
 

drumsbanger

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Amir,

I have a Chromecast Audio outputting from Toslink into a Schiit Modi Multibit DAC. From everything I have been reading, the Chromecast puts out a horrendous amount of jitter through its optical output. Thus, the iFi is recommended. Have you taken a look at the results from the output of the ifi being fed by a Chromecast? I just ordered the ifi, and I am wondering if I should cancel it?

Thank you so much for all your work. This is very informative.
 
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Hi Drumsbanger. Welcome to the forum. I do indeed have a Chromecast audio that I will be measuring soon. Didn't have the mini-S/PDIF cable initially but purchased one last week so I am good to go. Will report back soon.
 

mrmoizy

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Hi Drumsbanger. Welcome to the forum. I do indeed have a Chromecast audio that I will be measuring soon. Didn't have the mini-S/PDIF cable initially but purchased one last week so I am good to go. Will report back soon.
Hey Amir - sorry, this is an old thread, but I've been looking into this lately, and I've found some iPurifiers on ebay for a lot less than the $150 msrp. Did you ever end up testing this combination of a Chromecast Audio and the iPurifier?

Appreciate your work and contributions as always, keep it up
 

Tonjen

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Hi Amir.
Sorry to ask but did you ever test chromecast audio / ipurifier combination?
 

mimo

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This is a detailed measurement and review of iFi iPurifier. This is a device that is advertised to clean up your coax S/PDIF signal from all ills including the common flu to audio distortions. It is a tiny little box the size of a thumb drive:

index.php

Not shown is the fact that it actually needs external power and iFi ships it with their switching wall-wart "iPower" power supply.

This is not a filter device but rather, one that receives digital data over S/PDIF, buffers it (puts it in memory) and then retransmits it. iFi has a nice block diagram of it on their site:


Who wouldn't want their waveform cleaned up in red and turn it into the one in cyan? It is like getting an enema. Not that I have had one but I imagine it being the same.

Because the iPurifier regenerates S/PDIF, it should have good ability to remove incoming jitter. In a way it acts like an Ethernet switch/hub would for that connection. There is a problem here though. S/PDIF signal can drift in speed. It can run slower or faster than the stated sampling rate. For that reason, there is that memory buffer block in yellow. That is not a complete solution though as if the source runs faster than the internal S/PDIF interface in iPurifier, it could eventually fill up. The iPurifier has an undocumented measure for changing its clock frequency. That could cause fidelity issues and is something that is not easy to measure.

I bought my unit in August of 2017 for $149 shipped from Amazon. In other words it costs more than some decent DACs.

Measurements
Since this is a S/PDIF device and J-Test was designed for exactly this application, let's start with that. I programmed my Audio Precision Analyzer to output J-test while jittering the digital output to the tune of 4 Khz sine wave. I pushed that into Topping D30 DAC (review here: https://audiosciencereview.com/forum/index.php?threads/topping-d30-dac-measurement-and-review.2016/) and measured the analog output. I then did the same thing while routing the signal through iFi iPurifier:

View attachment 9896

Focusing on the direct interface in yellow, we see the two classic jitter sidebands. They are at +- 4 Khz relative to our main signal tone at 11.05 Khz. This shows that the Topping has little filtering of incoming jitter.

Running that signal through iFi iPurifier does away with that jitter as if it was not generated at all. So mission accomplished. Or is it?

I had induced quite a bit of jitter in there. Let's go with a real-life scenario of using a Gustard U12 USB to S/PDIF converter driving the Topping D30 DAC and see what inherit jitter we have and how much of it gets cleaned up by iFi iPurifier:

View attachment 9897

Not only did we not get a cleaner signal, but we got some added low frequency noise (in red) when we used the iFi iPurifier! Part of that is likely created by the iFi's switchmode power supply which leaks mains current. But there are other spurious signals there that I can't explain. Either way, we went backward here, not forward!

Let's try that with a different DAC, this time the Emotiva DC-1 DAC (full review later). The source is the digital output from my Audio Precision again, but without induced jitter. First let's look at J-test at 96 Khz:

View attachment 9898

Yeh the DC-1 puts out quite a bit of noise on its own. Alas, the iFi iPurifier did nothing but increase those levels slightly (in red). No good deed is left unpunished here!

Same story at 44.1 Khz:

View attachment 9899

We see the increased low frequency noise from iFi much better here. Not good.

Let's complete the round by driving the Topping D30 again using the AP:

View attachment 9900

Same picture again. Increased noise and distortion from iFi and no improvement elsewhere.

Let's go with a much cheaper DAC. Maybe those can benefit from this device. For that, I tested the Prozor 192 Khz DAC which costs $29 shipped!!! Here it is with induced jitter again, with and without iPurifier:

View attachment 9901

Yes, there is a whole forest of distortions there. What do you expect for $29 China special???

Addition of the iPurifier did eliminate the induced jitter (in yellow) but has done absolutely nothing for all the rest. Those are jitter/noise generated internally by the DAC and the ifi is ineffective there.

Let's jump to the other extreme and see what the $3,400 Exasound E32 does here:

View attachment 9902

As expected, a high quality DAC like this one completely ignores the induced jitter on its S/PDIF input. Addition of iPurifier therefore just added noise as show in red.

Finally, let's look at the "eye" pattern of the S/PDIF waveform in time domain. For this, I used the Audio Precision as the reference:

View attachment 9903

We see that the ifi output is slightly better (rises faster). But that is due to the fact that output of the iFi is directly connected to the DAC/Analyzer where as the output of the source had to go through a cable. In that regard, there is really no improvement here.

Conclusions
The only thing the iFi iPurifier is good at is eliminating high amounts of jitter on S/PDIF signal with lower end DACs. Despite what they show in their marketing material though, typical S/PDIF signal across a short cable is far, far cleaner than what they and their customers assume. The type of distortions and jitter we see in the output of DACs these days are mostly created internally and no external device can fix that.

Typical of these tweak devices shipped with switchmode supplies, combined with small enclosure means that this device can actually harm the output of the DAC! This was clearly visible < 2 KHz with various noise and spurious signals. Mind you, it is not an audible problem but why spend money to make the performance of your DAC worse?

At the higher end of the scale, good DACs have proper PLLs that filter out incoming jitter very effectively and no such device is useful or necessary.

Bottom line, I cannot find a real scenario where ifi iPurifier does any good. Yet it was easy to show that it does some harm. NOT RECOMMENDED.

Save your money for music, or a better DAC driven by isolated asynchronous USB signal.

As always, comments, corrections, feedback, etc. are welcome.

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I purchased one of these a while back, all in the pursuit of further fringe benefits.. but I can't test so glad to have found audio science and the work Amir does to help inform! On this device specifically, I did find many scenarios where I didn't see any impacts (eg on COAX SPDIF feeds from digital sources). Where I did see a difference (or should I say hear a difference) is not on my main two channel system, but rather in the living room where the source is the TV via Toslink to a TEAC AI-501DA integrated digital amp with internal DAC (DALI speakers). I'll often play music from the TV via a Google TV streamer that connects to the TV via HDMI (eg from the Tidal or Amazon HD aps etc). After failing to see any benefit in my main system and via COAX SPDIF, I figured what the hay may as well try on the living room setup. So, TV goes to this iFi device via Toslink and the device on the other end goes directly into the RCA COAX SPDIF input on the TEAC. Honestly, as much as there was zero impact in initial application on my main system, WOW, immediate and obvious impact here. I suspect the Toslink output from the TV was very very jittery and the reclock and maybe conversion to electrical COAX SPDIF that fed directly (ie no cable) into the REAC fixed at least most jitter. So perhaps the only use case is from a "low end" jitter prone Toslink out put to convert to COAX electrical SPDIF and feed directly into the RCA input. I realize it has been a long while since you did this review, but would be interesting to see this measured, ie TV Toslink direct into a mid tier integrated amp with onboard DAC vs. through this device and into the COAX SPDIF in RCA to compare jitter and sound. This to mean could be an interesting application with significant use (how many of us plug our TV audio via Toslink into an integrated? A lot I would guess).
So aharing in case you can measure and a potential useful application for others who may have purchased for main system before seeing your review..
Thanks!

(PS, main system where no impact was either PC via USB to a USB-TO-SPDIF converter and then into the RCA COAX SPDIF input of my McIntosh MCD500 SACD player, or from my MCD500 COAX SPDIF output RCA into my Holo May DAC SPDIF input.. or the TV in my listening room Toslink out into Holo May Toslink fiber optic input)
 
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