iFi S/PDIF iPurifier2 Digital Signal Optimizer
Tip #115
Dick Olsher (October 2026)

I first came in contact with this device a few years ago in the context of the Denafrips Terminator DAC. While its USB input sounded great, the S/PDIF coaxial input used for CD playback yielded disappointing results. Image focus and transient precision were noticeably degraded to the point that CD playback wasn’t much fun. In a desperate effort to restore parity between these two inputs I decided to give the iPurifier2 a try. I was surprised by and elated with the results it produced. It instantly became an indispensable part of my digital front end.

To enable the use of a single coaxial or optical cable to accommodate both data and clock, the clock which runs at twice the CD sample rate of 44.1 kHz, is embedded into the S/PDIF data stream using biphase mark encoding. There are two changes of signal for each data 1 transmitted and only one change for each data 0. Because the number of transitions fluctuates depending on the audio content, the recovered clock can suffer from data-correlated jitter.

The iFi iPurifier2 provides jitter reduction technology which includes a femto-precision clock. The incoming data stream is said to go through four stages: isolation, regeneration, a memory buffer, and re-clocking. In my experience, even expensive DACs often perform poorly on the S/PDIF inputs because they’re saddled with something like a Cirrus Logic CS8416 receiver chip and thus stand to benefit from the iPurifier2.

Unfortunately, because I waited so long to recommend it, I’m sad to report that the S/PDIF iPurifier2 has by now been discontinued. I can only hope that IFi comes to its senses and reverses course. In the interim, your best bet is the used market.