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:
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:
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:
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:
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:
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:
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:
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:
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:
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.
If you find this article useful, please consider making donations through Patreon (https://www.patreon.com/audiosciencereview) or if you are member, by "Upgrading your account" (see: https://www.audiosciencereview.com/...eview-and-measurements.2164/page-3#post-59054). The funding enables me to purchase more products and test.
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:
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:
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:
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:
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:
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:
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:
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:
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.
If you find this article useful, please consider making donations through Patreon (https://www.patreon.com/audiosciencereview) or if you are member, by "Upgrading your account" (see: https://www.audiosciencereview.com/...eview-and-measurements.2164/page-3#post-59054). The funding enables me to purchase more products and test.
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