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Somewhere here down in the Southern USA where the Euphonic Review lab stands, where my hobby (and primary career) is tickling the ivories, well, these days more like stomping out some Rockabilly Jerry Lee style (Rest in Peace dear Friend), I have been chasing a mystery only audiophile nerds care to chase down. Turns out I was not the only one.. wow!!! What a consternation was stirred up online regarding the iFi NEO iDSD, a new Performance edition, and various firmware updates. First, came the admission there is no difference in the original NEO iDSD hardware released in late 2020, and the hardware in the 'new' Performance edition. The differences in hardware consisted only of two add on accessories.. a USB iPurifier3, and a SPDIF iPurifier2. Turns out I already own the USB iPurifier. It is a solid little add on, and I found it to offer subjective improvements with certain USB DACs. The SPDIF version, unreviewed by me personally, I expect it to be and have read it be an excellent product, especially when it comes to eliminating SPDIF jitter, as it is galvanically isolated, and creates a pure, clean SPDIF signal for the receiver PLL, buffers and clocks, making their job with recovering a clean clock much easier. Of course, this didn't necessarily sit well with many people, that may have bought a Performance version expecting more for their money. And that is understandable. Things were not helped by a chart outlining the new 'upgrades' from the original version. These were later dismissed as, put into my own words, accidental misprints and miscommunication. I don't mind just a little speculation here at ER, and part of me wonders if part of this goes back to something the keen eye may have observed at the time; that the first release of the NEO to the public was version '1.1'. Perhaps there was one that came before that never made it to production and was quickly upgraded? Possibly. Again, I am just speculating. I find all the more curious myself though, is the insistence that the NEO iDSD PCM oversampling filter was locked with no other choice, and this filter locked in by firmware was the in-house developed (along with help from MQA) 'GTO' filter. The GTO filter is a short (32 tap) minimum phase FIR filter that you can read all about by clicking here. But the first major reviews with measurements showed that the filter on offer with the NEO iDSD was not the GTO filter. It isn't even minimum phase. HiFi News caught this but didn't challenge, seeming to assume their measured results were how it was supposed to behave. What they had measured was a moderately long linear phase filter with its expected stopband behavior. Now, there have been many firmware updates, so it seems, in the life cycle of this product, so things could have changed. My particular example of the hardware is version 1.1, with firmware 3.18. And just like HiFi News, my example has a slightly long linear phase FIR filter, with fairly strong stopband rejection. Definitely NOT the advertised GTO filter. To further muddy the waters, there seems to be multiple past firmware updates, that even allow the end user to choose the single, default filter in their NEO iDSD. PLUS, there is a firmware update NEWER than my version that opens up a host of iFi filter options, ala the Gryphon or iDSD Pro. I like iFi products. But I also like being a fair reviewer to all sides involved. So to be fair, this was a confusing mess that made a night of scrolling through the wailing and gnashing of teeth on Head-Fi time I wish I had back. I have already finished most of my benchmarking on the NEO iDSD with the 3.18 firmware. Now, I am off to upgrade to the latest and see what I can find... hopefully what I expect to find.. no trouble down here in the southland. Y'all come back now, ya hear? Please? As always THANK YOU for reading and supporting Euphonic Review.com  Definitely NOT the GTO filter  THIS is the impulse response of the 32 Tap Minimum Phase GTO filter as captured from my personal iDSD PRO. Not 'quite' the same thing haha
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