iFi Audio micro iDSD

 Introduction

Does anyone remember what portable, audiophile-grade playback used to look like? I certainly do. I remember going to Head-Fi meets and being in just awe of all the insane amount of paraphernalia attendees would carry around just to play their favorite set of digital bits. Take for instance the Headroom Micro line. Consisting of both a standalone DAC and headphone amp, the Micro line was originally conceived to conquer the low to mid-tier desktop market. But because it packed a lot of performance per square inch, many audiophiles opted to go with it instead of Headroom’s own dedicated portable line, the Airhead, as their go to portable stack. That’s why Headroom at the time even offered you a Micro sized fanny pack carrying case to help you transport your iPod’s BFFs everywhere you went.

Looking back though, it seems outlandish to me that any sane audiophile (Two words combined that can’t make sense. -Dave not Mustaine) would even consider lugging around an entire Micro line just to achieve a modicum of fidelity through their favorite digital source. But the fact is both the Micro headphone amp and DAC were considered state-of-the-art back in the day, and offered many bleeding edge features that we all now take for granted, including an asynchronous hardware reclocker with noise shaping and even crossfeed.

But technology improves at an extremely rapid pace, and what was state-of-the-art back then is now today’s garage sale bait. Yet if the Micro line was indeed the standard in which all portable stacks were judged back when dinosaurs ruled the Earth (circa 2005), then today’s equivalent would have to go to iFi Audio’s micro iDSD, which is nothing short of a technological marvel. Read on to find out why this $499 (street) little beasty is nothing short of spectacular.

iWho?

iFi Audio is a division of Abbingdon Music Research (AMR), a fairly well known and well respected high-end audiophile shop based in the UK. Their reference level CD player, the CDP-77 ($8,500), has been hailed by many as a real giant killer, conquering Redbook induced digititus for half the cost of some of its better known competitors. More recently though, AMR has been getting a lot of press for their single-ended triode amplifer, the AM-77 ($8,500), which brings valve-like sensibilities to your favorite reference chain of choice through the use of their proprietary OptiGain circuit.

Obviously given the price tag of your standard issue AMR component, the market for these devices is somewhat limited (though frankly $8,500 isn’t as outlandish as some of you might believe in the high-end audiophile world). So in order to expand their product line and appeal to a wider audience (read: younger), AMR spun off iFi Audio in 2012 as a separate business unit to develop audiophile grade products at a more affordable price point.

iFi Audio came running out the gate releasing a number of products that spanned all four corners of the digital and analog world, ranging from the iPhono (with no less than six different EQ curves to choose from) to the iUSB (the Arm & Hammer of USB power). In fact, very recently they just updated their well respected iDAC, which as many of its owners will attest to, laughs in the face of other DACs (portable or otherwise) that claim “high-res” support. But out of all the micro products they offer, I feel the micro iDSD, a combination DAC/headphone amp, is by far the most representative of AMR’s trickle down economics approach.

Crowdsourced Design

 

After iFi reached critical mass with its 2012 introductory product line, the folks over there did something very smart: They sought direct community feedback during the design phase of their next iFi product. The net result of this social experiment can be found in the massive micro iDSD thread over on Head-Fi, where iFi not only collected feedback from the entire audiophile community at large but used this forum space to document the overall design process as well. If you have some free time to spare, I highly recommend you read all of the cherry picked posts referenced in the first post’s table of contents section. iFi literally walked you through almost every major design decision they made, ranging from how they wrote some custom scheduling code to load-balance the numerous XMOS cores to how they implemented a reference level clock inspired by a missile guidance system. Trust me when I say that this thread is not only extremely informative, but very well written and at a level that even a non-technical audiophile will find fascinating to comb over.

Digital Done Right

The iDSD has been one of the most difficult pieces of gear I’ve ever had to review simply for the fact that it is so feature rich. I could probably spend an article or two just talking about its DAC – seriously. In any event, in an effort to keep things organized let’s dive into its digital side and then slowly make our way to its analog half.

As you can see above, at the heart of the iDSD is a pair of Burr-Brown Multibit DACs that offer true native DSD and PCM support, the exact same chipset found in the nano version of the iDSD. But by adding a second double B, iFi was able to lower the noise floor by 3 dB as well as improve channel separation to boot! But like the nano version, the micro’s firmware employs the same novel approach to PCM conversion as well.

Unlike most delta-sigma architectures that convert everything to a 1-bit stream first before filtering, the iDSD preserves the high order 6-bits of a PCM data stream and only converts the rest of the low order bits via its internal 256fs (DSD256) modulator. iFi claims that this allows the iDSD to keep some of that Burr-Brown signature warmth while still retaining all the smoothness delta-sigma modulators are so famous for. Obviously for pure DSD input, those Burr-Brown’s handle it natively using that same DSD256 modulator to convert to analog. And since iFi used the latest and greatest chipsets, the iDSD is able to handle an insane number of sampling rates, maxing out at Octa-Speed DSD512 and PCM768 (2x DXD)!

Keep in mind that the iDSD is truly native with respect to DSD playback, so all volume control is done in the analog domain in an effort to stay true to the original bitstream. In other words, unlike a lot of DSD capable DACs that transcode to PCM first in order to apply digital volume control, the iDSD always preserves the original signal as is when converting 1’s and 0’s to electrons.

 

Feeding these two DACs is an eight-way XMOS U-series based chipset, which is one of the premier USB receiver solutions on the market. Now if you are vaguely familiar with XMOS that’s probably because you’ve heard about it in the context of some ESS SABRE based solution, since the combination of SABRE and XMOS seems to be the defacto reference platform most audiophile products are based on today. I suspect though that iFi choose the XMOS (as opposed to something like a high-end C-Media chipset a la Schiit) not for its industry wide popularity but mainly because of its high-processing power (MIPS) and ease of development. In fact as I mentioned above, iFi’s software team went to town on the XMOS, not settling for the reference implementation provided by the vendor but actually writing their own custom firmware to better utilize all eight cores. Couple that with built-in iPurifier support, the iDSD has one of the most advanced USB solutions on the market today at any price point.

There was also expressed interest by many Head-Fi’ers to have selectable digital filters just like you would find on the Herus+ dongle I reviewed recently. iFi listened and implemented two sets of three selectable filters depending on whether you are playing PCM versus DSD. For PCM based input, you have standard, minimum phase, and bit perfect, while for DSD you have extreme, extended, and standard. Sticking with PCM since that is by far most of what your brutal bits are encoded in, the standard filter offers the most accurate digital filtering at the cost of some added ringing. While the minimum phase and bit-perfect filters seem to be the most popular for actual listening among audiophiles, exhibiting the least amount of pre and post-ringing with respect to transients. DXD sampling rates have no filtering applied whatsoever and are converted to analog as is (as they should be).

With Great Power Comes Greater Responsibility

As for amperage, the iDSD puts out an astounding amount of power with enough lightening to sizzle most full sized headphones. The key to taming this beast is through the Power and IEMatch mode switches located on the side and its underbelly respectively. The Power mode switch is by far the most important setting on the iDSD and the one you have to get right or you can blow up your favorite pair of transducers easily. It can be broken down into the following modes: Eco (500 mW at 8 ohms), Normal (1900 mW at 16 ohms), and Turbo (4000 mW at 16 ohms). Trust me when I say that the overwhelming majority of you will always be headbanging in Eco mode. However, if you really do own a hard to drive headphone (think HE-6) then you can use the Normal and Turbo modes as appropriate (yes, Turbo mode will drive the AKG K-1000 handily).

After the Power mode switch is finalized, then comes the IEMatch mode switch. Again, for full sized cans you are probably going to leave this switch in the off button for the life of the unit. But if you do plan to use really any kind of IEM (especially CIEMs) then the two other modes, High Sensitivity and Ultra High Sensitivity, are your friends. In order to figure out which setting will work best for your particular headphone, iFi offers the following chart:

Common sense applies, so using Ultra High Sensitivity in Turbo mode is for those looking to earn a Darwin Award. For the rest of us however, iFi recommends that in general you want to be able to listen to your favorite pair of headphones at normal volume levels at the 3 o’clock position of the volume knob. That’s the sweet spot, so start in Eco/Off mode and then gradually increase the Power and/or IEMatch buttons as needed. Trust me, it’s not hard.

Speaking of power, the iDSD allows you to work directly off of its internal 4800 mAH battery or USB via its SmartPower circuitry. The order of when you connect the iDSD via USB and turn the unit on is very important: Turn on the unit before connecting it via USB tells the firmware to operate on battery power exclusively. Conversely, if you connect the unit via USB first and then turn the unit on, the iDSD will operate off of USB power instead. For iPhone and Android potential customers, iFi recommends that you use iDSD in battery power mode exclusively, since you may experience some device errors otherwise. Caveat emptor. And yes, the unit will charge while playing music too. In fact, the iDSD can even charge your favorite smart device up to two times while in use! And in case you’re wondering how do you tell when you are running out of juice, there is an LED status light on top of the unit that based on its color will tell you all sorts of useful information. Again, with great power comes greater responsibility. Use it wisely.

Odds & Ends

In terms of inputs outside of USB, the iDAC accepts optical and coaxial SPDIF via one port in the back and another 3.5 mm one in the front. The SPDIF input on the back also serves as output if you don’t have any headphone connected. For outputs, you have your standard red and whites on the back (RCA) and the single 1/4″ headphone jack in the front. And yes, the iDSD can essentially mimic a DAC/preamplifier via those RCA outputs by switching it out of Direct mode into Preamplifier mode by toggling a switch toward the rear of the unit.

The volume knob controls a specially designed potentiometer (POT) made specifically for the iDSD, and apparently gives you slightly better control (<2 dB tracking error)  than your standard issue ALPS. The two other switches next to it are the XBass and 3D Holographic Sound switches. When XBass is turned on it gives you a nice noticeable bass boost. The 3D Holographic Sound is iFi’s cross feed circuit, which you may or may not dig. Disclaimer: I’m not a big fan of crossfeed in general.

There is also a polarity inversion switch which for some of you out there on strong meds might find useful. I’ve never experienced any particular need to invert the polarity of the output so I’m highly confident that 99.9% of you aren’t going to use it either.

Finally, in case you haven’t noticed from the pic above, the iDSD comes with a myriad array of adapters, and even includes a high quality USB 3.0 cable to boot. Once you open that box, you’re set. For life. Seriously.

Setup

As usual, my primary source was my trusty late-2011 Macbook Pro running OSX Yosemite 10.10.4 and Audirvana 2.2. For full sized cans I switched back and forth between my Audeze LCD-3 (non-fazor) and HiFiMan HE-1000, both powered by Eco mode with IEMatch off. That allowed me to listen to both headphones at normal volume levels around the 3 o’clock position. Check. I also tried my JHA Roxanne CIEM in Eco mode but with Ultra High Sensitivity turned on which also worked like a champ – zero hiss, total black background. In addition to USB, I decided to plug in my Audiophilleo AP1 with PurePower USB to SPDIF converter to give that a go as well. Everything worked as expected but surprisingly I felt the USB input sounded better overall and as a result, became the primary way I escorted bits off of my MBP for this review.

I also played a lot with the digital filter switch too, ultimately settling on the BitPerfect filter. Again, your mileage may vary, but I would start with BitPerfect, or maybe even Minimum Phase first, before randomly moving that switch around during playback.

One final setup note: I had one technical problem I was not able to overcome switching back and forth between DSD and PCM with Audirvana. If I play DSD and then switch to PCM (no matter the resolution), I get a lot of noise and distortion as if the unit and/or my headphones are completely toast (He was freaking out the first time it happened. Trust me. -Dave). I had to manually reset the unit by disconnecting it from the USB port and then plugging it back in again to reach a steady-state. This issue seems to be relegated to Audirvana only though, since I tried foobar2k under Win 7/VMware Fusion without any problem. Interestingly enough, Audirvana auto-recognizes that the iMicro supports up to DSD256 even though it really supports up to DSD512. This is due to the fact that the DoP spec (DSD over PCM) only supports up to DSD256 currently on OSX (I believe on Linux you can tweak the kernel to get DSD512 to go, but obviously I have no such luxury on my Mac).

Sound

You made it!

Alright, despite the fact that the iDSD supports a plethora of sampling rates and formats, I’m quite aware 99% of your time will be spent with 16-bit/44.1kHz PCM source material. With that said, just the ability to play these insane-rate files seemed like a lot of fun. So what I did was go to Native DSD’s website and download a few free samples of various high-res formats, including DXD (32-bit/384kHz) and DSD128/256. I then plugged in my HE-1000 and off I went. Suffice it to say everything just worked! Was I amazed by the sound though? Not really, but frankly I didn’t spend a lot of time critically listening to each download sample nor did I have any equivalent source material in standard definition format to really compare it to. Couple all that with the technical glitches of switching back and forth between DSD and PCM, I decided to move on.

As a first test, I wanted to listen to some high-quality reference material to see what this puppy can really do. That means high dynamic, well mastered source material a la Horrendous’ Ecdysis. This record is one of the best death metal albums to come out in a long time and Horrendous guitarist/engineer Damian Herring did a bang up job producing it, clocking in at DR10. And after blasting tracks “Weeping Relic” and “Monarch” I quickly realized just how good the iDSD is given its price tag. First off, detail retrieval is outstanding, with every track on this record just beaming with life. Transients are of particular note, having a very fast attack and then natural sounding decay as the dual Burr Brown’s have no problem keeping up with band’s various tempo changes. Bass is absolutely ear boggling too, with or without the XBass switch on. But what I found most gratifying is that unlike a lot of its competitors, the iDSD’s overall presentation is open and wide. Any compressed sense of soundstage I was hearing was more an artifact of the headphone I was using than it was from the iDSD itself. Put simply, the iDSD has a way of politely removing itself from the playback chain, letting the music just speak for itself. A hallmark of every great piece of audiophile gear.

Unfortunately, given how revealing the iDSD can be, I was immediately worried that Loudness War governed music would not fair as well, and to some extent I was right. As soon as I threw heavily compressed records like Strapping Young Lad’s 1997 classic, City, or the recently released Trials record, This Ruined World, the iDSD’s wonderful sense of airyness vanished due to both record’s heavily reliance on dynamic range compression. Obviously, this isn’t the fault of the iDSD per se, but just be aware that this unit is quite resolving for better or worse. The good news is that the added warmth of the Burr Browns does actually help alleviate ear fatigue over long listening sessions. However, I would absolutely avoid even looking at the 3D Holo switch, since iFi’s crossfeed implementation pushes the midrange to the fore which for most highly compressed material utterly destroys the music (imagine the Grado house sound on steroids). Usage of the XBass switch is certainly encouraged, especially if you have a can that is known to be somewhat anemic down low or you just want to have a little fun.

Finally, a Metal-Fi review would not be a Metal-Fi review without some kind of needle drop. So I dusted off Nokturnal Mortum’s Voice of Steel from my collection and just sat back and listened. Bass control again, is just phenomenal, and that rang true no matter what headphone or IEM I used. I also felt that the midrange was exactly where it needed to be – prominent, but not to in your face, and having just enough analog warmth to help round out some of that digital edge we’ve all come so accustomed to. Some of you may find that unacceptable if strict transparency is what you seek, but for the rest of us who are out to simply enjoy the music the iDSD hits the nail right on the head. And while the treble doesn’t shimmer like I’ve heard on systems many times its price, the iDSD’s command of the upper frequency range is quite respectable. Not once did I feel somewhat grossed out by the crash of a cymbal or tap of a hi-hat. Something I can’t say the same for a lot of SABRE based products I’ve listened to.

Conclusion

The iFi micro iDSD is a phenomenal piece of gear, incorporating state-of-the-art digital design in a beautifully well thought out package. In fact, my single biggest complaint is that the iDSD isn’t really portable, but rather transportable. I mean of course you can lug it around if you really had to, but it doesn’t make a whole lot of sense these days given the rise of the dongle form factor. But portability issues aside, when it comes to both fidelity and feature set the iDSD is clearly the current standard in which all other devices in this segment should be judged. No question. My guess is you would have to spend at least triple to four times the price to best this little box, and even then I suspect the differences will be paper thin. If you are looking for a multi-faceted desktop solution at a very reasonable price point, your quest is over. Highly recommended.