This is a review and detailed measurements of the ifi iPurifier 3 "USB Audio and Data Signal Filter." It is on kind loan from a member and costs US $149.
The iPurifier 3 comes in a gorgeous and nice to feel ceramic (?) enclosure. The enclosure give is enough weight to feel substantial but not too much as to strain the connector. It is an in-line device and comes with three useful adapters which should cover all your USB connection needs.
In case you are wondering what this is for, here are the company specs:
Think of it as a USB repeater of sorts. For the purpose of this review, I take for granted that it does all of the above. Question becomes if our audio DACs need such an upstream device to "clean" their USB connection.
ifi iPurifier3 Measurements
My favorite device for testing USB signal quality is a Schiit Modi 2 which in the past has show very high sensitivity to conditions of that signal. So much so that I could measure differences USB cables make when connecting to it! I started by measuring the DAC by itself using a 6 foot USB cable:
There was a ton of noise in the FFT spectrum with the noise floor jumping up and down every few seconds (no doubt due to activities in my PC). That in turn caused the SINAD to vary continuously between 84 and 91 dB. This variation is system specific and could be worse (or better) on other host computers.
Next I put in the iPurifier3 inline:
There was a significant reduction in the noise floor as show in FFT and power supply related spikes. There were still jumps but much less in amplitude. SINAD was now very stable. So clearly such filtering was good for the Modi 2.
One could stop here and think that this is a useful device. But such is not the case because any DAC with half decent design would isolate itself against USB vagaries. To show that, I grabbed the Schiit Modi 3+ which costs just $99 to test. Here it is by itself:
We see massive decrease in noise floor compared to Modi 2. Predictably, it doesn't need any help from iPurifier3:
I almost stopped here but noticed there was some increased spike toward end of the spectrum. I decided to run the Jitter test with and without iPurifier3:
We see much increased spurious tones at 8 and 16 kHz. This corresponds to a jitter component of 4 kHz (12-4 and 12+4 kHz). I can't directly point to the cause of this but can guess that an extra inline device that uses power like iPurifier3 is going to degrade available current to the DAC. Fortunately the increased jitter rises up to only -120 dB which is below threshold of audibility -- again a sign of well designed product (Modi 3+ DAC).
Conclusions
It seems that the iPurifier does what it says it does: clean up the signal/power lines over USB and with it help devices that need it. Then again every DAC I recommend of which there are probably 50 to 100, already perform their own filtering and don't need any help. After all, I test them all on my desktop workstation without any such filters. Adding an active device to the USB connection can reduce available power and potentially decrease measured performance as show in the case of Schiit Modi 3+. Seeing how a better DAC costs less than iPurifier3 anyway, there is no reason to deploy such a device.
I can't recommend the ifi iPurifier3. Put your money toward a good DAC and sleep easy!
-----
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
In case you are wondering what this is for, here are the company specs:
Think of it as a USB repeater of sorts. For the purpose of this review, I take for granted that it does all of the above. Question becomes if our audio DACs need such an upstream device to "clean" their USB connection.
ifi iPurifier3 Measurements
My favorite device for testing USB signal quality is a Schiit Modi 2 which in the past has show very high sensitivity to conditions of that signal. So much so that I could measure differences USB cables make when connecting to it! I started by measuring the DAC by itself using a 6 foot USB cable:
There was a ton of noise in the FFT spectrum with the noise floor jumping up and down every few seconds (no doubt due to activities in my PC). That in turn caused the SINAD to vary continuously between 84 and 91 dB. This variation is system specific and could be worse (or better) on other host computers.
Next I put in the iPurifier3 inline:
There was a significant reduction in the noise floor as show in FFT and power supply related spikes. There were still jumps but much less in amplitude. SINAD was now very stable. So clearly such filtering was good for the Modi 2.
One could stop here and think that this is a useful device. But such is not the case because any DAC with half decent design would isolate itself against USB vagaries. To show that, I grabbed the Schiit Modi 3+ which costs just $99 to test. Here it is by itself:
We see massive decrease in noise floor compared to Modi 2. Predictably, it doesn't need any help from iPurifier3:
I almost stopped here but noticed there was some increased spike toward end of the spectrum. I decided to run the Jitter test with and without iPurifier3:
We see much increased spurious tones at 8 and 16 kHz. This corresponds to a jitter component of 4 kHz (12-4 and 12+4 kHz). I can't directly point to the cause of this but can guess that an extra inline device that uses power like iPurifier3 is going to degrade available current to the DAC. Fortunately the increased jitter rises up to only -120 dB which is below threshold of audibility -- again a sign of well designed product (Modi 3+ DAC).
Conclusions
It seems that the iPurifier does what it says it does: clean up the signal/power lines over USB and with it help devices that need it. Then again every DAC I recommend of which there are probably 50 to 100, already perform their own filtering and don't need any help. After all, I test them all on my desktop workstation without any such filters. Adding an active device to the USB connection can reduce available power and potentially decrease measured performance as show in the case of Schiit Modi 3+. Seeing how a better DAC costs less than iPurifier3 anyway, there is no reason to deploy such a device.
I can't recommend the ifi iPurifier3. Put your money toward a good DAC and sleep easy!
-----
As always, questions, comments, recommendations, etc. are welcome.
Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
