(REVIEWED IS THE NON-SIGNATURE EDITION WITH 4.4mm PENTACONN OUTPUT)
Review by Andrew Ballew
I have been poring over my many pages of notes, recalling many late nights of listening, familiarizing and refamiliarizing myself with the beast called the iFI iDSD PRO, that was at time of first release only $2,499. There is so much going on here, potentially, and there is all so much going on here very WELL, potentially, that any review attempt is intimidating, and a real responsibility to listeners, enthusiasts, engineers and companies alike. I must do it some justice. I finally decided there is no way I could really cover in depth ALL that this DAC/Headphone Amp/Preamp has to offer, so I came up with a flow strategy that makes its way through the most important things (to me, and hopefully to most of you). You can click on the box above marked ‘information/specifications' or you can click HERE to get a full rundown on what this thing can do, and then you may come back and continue with this review.
I will say this before I begin. I never took advantage of any of the ‘pro’ features (other than the DSD remastering engine), such as the higher voltage output or the external clock sync. I never tested the ethernet or Wi-Fi connections either. Not that these things are not important; simply put the implementation in the iDSD PRO is in electronics time, ancient to put it nicely, and something like the iFI ZEN STREAM is much, much more capable and if you are looking to use this as a network DAC, you need not hesitate and buy a ZEN STREAM as your iFI wi-fi and ethernet gateway into the networked music world. Oh, and I never tried inserting an SD Card for music playback. If you were looking for feedback on that feature, simply email me and I will test the feature for you. I DID, however, spend countless hours evaluating this device through various filter and oversampling modes. I spend a great deal of time comparing the internal DSD oversampling to that of HQPlayer. I did this as best I possibly could, because any computer that can oversample your audio to 1024fs in HQplayer is gonna be a technological monster. (Hint. Mine isn’t.) My ‘reasonable’ PC could ‘only’ oversample all audio to 256fs with consistency.
Finally I spend a lot of time comparing the headphone amplifier of the iDSD PRO to the latest headphone amplifier ‘breakthrough’ or ‘fad’ depending on which side of the stands you sit. This means I did a lot of comparisons using a THX AAA amp; this one being the reputed Benchmark Audio rival- the S.M.S.L SP400.
A lot of listening, yes, indeed. Most of my review was spent with just the equipment and software I will now enumerate. Roon with latest software updates running on a HP All-in-one PC connected via Audioquest Cinnamon USB cable to the galvanically isolated iDSD PRO. Primary listening was done via the iDSD PRO headphone output in its medium gain mode marked as 9db. The headphone used for most of the review was the truly unbeatable for the price Focal Clear MG in balanced mode via the iFI iDSD PRO 4.4 Pentaconn output. I also used the venerable Sennheiser HD650 in the process, and my personal cult favorite, an early version of the Hifiman HE560 planar. No listening was done in single-ended mode.
The iFI iDSD PRO review begins with ‘Tube Mode 1’ as the analog output. This is a standard tube output with a fair share of feedback for better linearity. To begin with, I chose the Gibbs Transient Optimized Filter (GTO), explained in detail by clicking here. The GTO filter has much in common with the third-party Meridian MQA output filter, but note: albeit philosophically similar, it is NOT the same filter.
I used Tidal from within Roon to pull up my Bill Evans playlist and turned to the album ‘Trio 64’. Trio 64 was released in 1964 with Evans on Piano, Gary Peacock on Double Bass, and Paul Motian appearing for the last time ever with the trio on drums. Music critic Lindsay Palmer wrote of the album: “The effort spotlights their communal and intuitive musical discourse, hinging on an uncanny ability of the musicians to simultaneously hear and respond.”
The iDSD PRO has an uncanny ability to dig deep into the micro-details without ever sounding sharp or harsh. While listening to the first track of the album, 'Little Lulu (Master Take)' in 16bit/44khz via Tidal, I noted more-so than with any other DAC I have in my lab, the clarity of Gary Peacock’s ‘nonsense singing’ during his masterfully improvised bass cadenzas. A marker one is listening to something more than the average digital audio processor is exactly how much detail is extracted from the recording, and exactly how very, very natural and listenable it still is. The iDSD PRO has comfortably passed the first marker with good performance. Outstanding, actually.
Imaging is especially good. Each of the three instruments of the Bill Evans Trio is easily pinpointable in space using the iDSD PRO's 4.4mm balanced Pentaconn headphone output driving the Focal Clear MG headphones. The soundstage extended well past the edges of the headphones, almost 3D like. Not only does it stretch from left to right, but there is also good spacing between instruments front to back, which for whatever reason seems to be a less and less common trait I find as I review these types of devices. Bass is well defined with a certain amount of tube ‘roundness’ that never distracts; it only enhances. Percussion is always smooth, never harsh and has long, satisfying decays on cymbals, combined with quick transients as required on toms, snare or bass drum. At times there was an edginess or hardness transmitted by the piano; however, I am not using the stock tubes as chosen by iFI Engineers. This may play somewhat of a part. CLICK HERE FOR MORE INFO ON TUBES USED IN TEST.
Staying right where we are, I made one change. I switched the tube output to ‘PLUS’ mode. This mode reduces negative feedback and by nature will have higher harmonic distortion. I have stated in my writings here at Euphonic Review and at other places that I don’t find ‘harmonic’ distortion offensive. It is called harmonic for a reason, following the musical overtone series that for the lower harmonics is consonant in nature, consisting primarily of octaves and perfect intervals. Granted it is NOT original to the recordings hence it called distortion no matter how pleasant it may be. However, when one is listening to his or her hi-fi system, winding down after a long day, perhaps with a glass of wine or even something with some Tennessee whiskey or our homebrew 'White Lightnin' for the brave, I am not sure that harmonic distortion is on the mind; rather- how enjoyable, relaxing and engaging the music is surely takes priority.
The test bench really dislikes this mode, with its MUCH higher harmonic distortion, and therefore notably lower SINAD. Despite the lower SINAD, the actual noise floor stays very, very low however, which is a mark of a well-engineered, high-end product. Nothing else changed in the configurations, either. Nada. Same source, same album, same track, same GTO filter. The only difference is changing the level of feedback used in Tube Mode PLUS. Imaging starts to ‘meld’ together just a little bit in Tube PLUS mode, but there is even less hardness or harshness in this mode. The piano harmonics should be greatly increased in this mode, but any hardness or edginess detected in the original Tube Mode 1 is gone. Transients strikes on the track 'Little Lulu (Master Take)' via Tidal came across very nicely. They were crisp, tight, yet had a greater sense of ‘fullness’ than they did in “Tube Mode 1” and sounded more musical and natural. As nicely reproduced as percussion was in ‘Tube Mode 1’, in ‘Tube Mode PLUS’ the overall smoothness without sacrifice of detail or transients was next level.
Staying in ‘Tube Mode PLUS’, I switched the filter from GTO to Bit-Perfect, for non-oversampling filtering and conversion. Yes, even though iFI DACs use TI DSD1793 chips that are part delta-sigma -- when processing PCM, the most significant 6 bits are rendered as non-oversampling with scrambling/dynamic element matching before conversion of each of the 6 bits (64 bits unary/thermometer code) into current.
When this mode is measured, the results look identical to 100 percent R-2R PCM DACs in NOS (non-oversampling) mode, yet this process has a real advantage over true/full PCM or R-2R ladder DACs. Once the audio reaches the least significant bits, that is, bits 7 and below in a 16 or 24 bit file, The “zero crossing” errors that plague full PCM R-2R DACs are avoided due to the very nature of the hybrid/segmented converter.
After listening for hours and hours with the GTO filter, immediately the NOS Bit-Perfect and the related Bit-Perfect Plus filter have a truly unique and natural sound to them. The GTO filter, which is designed to have NOS like filter characteristics without its drawbacks, could not quite duplicate the clarity and detail of the Bit Perfect filter, especially Bit-Perfect Plus, which is a single tap filter designed to counter the loss of treble energy that is inseparable from any ‘NOS’ (Non-oversampling or Bit-Perfect filter) due to the sinc effect. However, the GTO filter was still the overall winner to my ear, as the Bit-Perfect filter at times could be a tad harsh. Never did I experience any harshness with the GTO filter.
At this point, I was by and large enjoying the low-feedback analog ‘Tube Mode PLUS’, versus the standard ‘Tube Mode 1.’ ‘Tube Mode PLUS’ was preferred for long and blissful listening sessions. We will get to the solid-state output mode later in the review, but I wanted to take some more time to discuss filters to give you as much information as possible about all filter possibilities.
After extensive listening time dedicated to both the GTO and Bit-Perfect filters, I turned my attention to the apodizing filter. I have a sweet spot for apodizing filters. Yes, they can be a bit finnicky at times and I would never recommend one in a ‘one filter fits all’ approach. However, the apodizing filter on the iFi iDSD PRO FPGA is very good, and many will find it to be a most inoffensive filter. Every listener will likely find something about it listenable and enjoyable. However, by my personal estimation it is again not the best filter on 'tap' here. Indeed, the filter did everything well, and nothing stuck out as odd. The soundstage is perhaps a bit larger and more reverberant, as expected. However, by digital filter standards this is NOT a very long filter at a mere 128 taps. This is long enough though for post-ringing to be audible to the human ear, but perhaps not enough so that one should discount the filter. The apodizing filter is a very competent filter with an excellent sound, but compared to the GTO and Bit-Perfect filters, in a single word, I did find the apodizing filter somewhat ‘boring.’
The next filter is a bit of a doozy for political reasons that I will not really get into, (except on reflection I kind of did) but perhaps you can read between the lines. There is a major audiophile company that has a philosophy that favors filters with the most amount of taps possible. The sharper and steeper the filtering, the (supposedly) more accurate the reconstruction and the more realistic the transient response should be. There are plenty of audio engineers who balk at this strategy, and I am an enthusiast that finds the idea of a filter with millions of taps that filters out unwanted frequencies to essentially oblivion, including frequencies necessary for transient response, somewhat questionable on the best day. Basically, the idea is to use millions of taps to ‘perfectly’ reconstruct the frequency domain. Time domain is given no real thought here except the hypothesis that perfect frequency domain will naturally mean perfect time domain response. This seems to fly in the face of everything digital audio engineers have learned over the last half century. The accepted 'dogma', and for good reason, is to gain performance in time domain, you will lose it in frequency domain, and vice-versa. The iFI iDSD PRO Transient Aligned Filter is programmed to emulate this kind of popular filter used by a company whose name may or may not rhyme with Ford. The reason that the iFI implementation has ‘only’ 16,384 taps, is because, and I am not kidding here...to have more taps requires permission from said company that rhymes with Ford, since they seem to have a patent on super long FIR filters??!! Huh??? Whatever the actual legal case may be, if you enjoy the sound of that type of filter, iFI has you well covered. Well, covered as well as they legally can. Over 16,000 taps is a whole lot of taps, and it sounds as I would expect it to. Extremely open and spacious, because this filter is like I would expect- an extremely long filter with an offsetting delay, and so many taps the echo from the delays will start producing easily audible reverb. I must admit it does make for a very, very seductive and likable sound. If that is the sound you like, then more power to you! Go for it. I realized awhile back the same argument about tubes and SINAD could be used against me, but I don’t care because I like the way tubes sound. If super long FIR filters contribute to the sound that you like? Don’t ever be ashamed of what sounds good to you. An entire company has been built on the exceptional sound produced by this type of filtering. And if this is the filter you enjoy using with the iDSD PRO? Go for it and be proud! Also I well understand that I could be completely wrong on this kind of digital conversion strategy and it truly is the highest tech thing really out there. My mind is very open. But, as of today, NAH, just no love from me.
Speaking of tubes, we now leave the tubed modes of operation and head to the iDSD PRO Solid-State analog output that replaces tubes with J-FET’s. No other parameters have changed in the review: the iDSD PRO headphone output is still in use driving Focal Clear MG headphones, and Roon software is still the front-end. Bill Evans album ‘Trio 64’ is still my choice of review music. As I see it, comparing all the different modes with the very same musical tracks is important as it eliminates the recording itself as a variable. The Filter of choice is GTO. In SS (Solid-State) mode, the iFI iDSD PRO is exceptionally clear and clean, with spot on timbre. There is excellent spaciousness to the sound and anywhere from good to great imaging or separation. I tried out the Bit-Perfect filter modes is Solid State mode. I must say, I liked Bit-Perfect filtering even more here on the Bill Evans material. This was some of the best lower frequency microdetail I have heard that still had good ‘thump’ and ‘roundness’ to the tone, but without once ever sounding ‘bloated’, ‘boomy’, or ‘unnatural’. That said, as nice as the Bit-Perfect filters can sound situationally, I still find the GTO filter to still be the overall star of the show.
While staying in Solid-State mode, I left behind Bill Evans and all 44.1khz recordings for some high-resolution material. I turned to Diana Krall's 24/96 Verve album “When I Look into Your Eyes” and used the track ‘Let’s Face the Music and Dance’ for critical listening. Sticking with what I learned about the iDSD PRO filters, I listened first with the GTO filter activated. Krall’s voice was so perfectly highlighted in the center, pushed forward, but not so much that the rest of the track is lost. It was so easy to hang on every sultry vocal movement; the presentation was so striking one could almost visualize every movement and quiver of her lips at the microphone. I have heard this track a bit too sibilant and harsh on other DAC’s, but that is not the case here. While the ‘esses’ are indeed prominent, they never approach the point of being distracting or painful. I believe the iDSD PRO gives a near perfect reproduction of the track; besides Krall’s splendid voice, all the other instruments are clearly delineated in their proper space and timbre is spot on. Strings are smooth as silk. Never a harsh sound, yet their overtones nonetheless soar beautifully into the high frequencies. Now the GTO filter is separating itself even more from the others at higher sample rates. While I found the two Bit-Perfect modes at their best with 44.1/48khz files, it is very clear to me that the GTO filter is working its ‘magic’ on this 96khz file.
No review of the iDSD PRO is complete if I leave out my findings on one of the major, if not THE major feature of the iDSD PRO, and that is the iFI proprietary FPGA DSD Remastering Engine that will oversample all PCM file rates, and all DSD files rates at 256fs and lower, to DSD512 or DSD1024. When you are remastering PCM files to DSD, all filter options are available for reconstruction/oversampling of the PCM file. Just as with ‘standard’ PCM conversion, you have all the same filter choices available in the DSD remastering process to tailor the sound to your liking. When it comes to DSD to DSD oversampling, this is not the case. The remastering engine will use its proprietary FPGA programming to prepare the lower rate DSD stream for re-modulation to either DSD512 or DSD1024. So how does it sound and how does it compare to other DSD processing engines? First, the FPGA and proprietary software used in DSD remastering on the iDSD PRO is very, very powerful. It works perfectly, is always stable, and always has studio grade sound. The reason this iDSD PRO review is a bit delayed is I wanted to get a comparison of the iFI engine with the Signalyst HQPlayer PC based software engine. The first major win in the iFI corner is its easy one or two button press for conversion up to DSD512 or DSD1024. HQPlayer takes SERIOUS hardware to make it to DSD512, let alone DSD1024. It s a major win for the iFI iDSD PRO to have this powerful studio grade oversampling to DSD1024 without needing the high-powered hardware required to run HQPlayer properly at its very best.
HQplayer wins for flexibility, though, and overall is a tremendous DSD engine, especially for those that DO have the hardware power to pull it off. As far as sound is concerned? I am somewhat limited when I use HQPlayer because I don’t have the hardware to go past remastering to DSD256. However, from what I have been able to hear, the two engines are neck and neck for sound quality. If I had to pick one over the other? If I had a state-of-the-art PC, I would go with HQplayer because of the sheer flexibility and obviously it can be used with ANY DAC that supports DSD.
The iDSD PRO is a true DSD DAC, with no DSP whatsoever in its native 'bit-perfect' DSD mode. There are no conversions of any kind, never a time when the signal is multi-bit*, there are no oversampling filters, no sample rate converters, none of these things. When a DSD file enters the DAC, the only processing it is subject to is the final FIR filter that converts it to analog. *One could argue that the FIR conversion filter produces a multi-bit file, however, I would say at this point it is no longer a digital signal. It is the contiguous analog signal output of an analog FIR filter. Individual currents (in this case 8 since there is a 8 bit delay line) are combined into a single analog current that will be converted to an analog voltage. The bottom line is, a native DSD DAC has but a single FIR filter that outputs an analog signal. In addition to the primary FIR conversion filter, there is usually a second analog reconstruction filter following the first. This is the case with all iFI products. The following 'final' filter in the iDSD PRO is a simple analog RC filter with a -3dB cutoff at 80khz. This 80khz filter ALSO has a servo control that raises the volume of DSD files by 6dB, in order to equalize the volume difference inherent in two different encoding systems. As far as 'pure native' DSD is concerned, the *FPGA oversampler certainly adds its own complexities. But it is completely defeatable and the downstream DAC is as simple as it gets, and that is what we want. When it comes to high quality audio, less is more.
Even using HQPlayer third party software, the results will be similar in that a true 1-bit DSD file will be converted to analog via the DSD1793 chip using the same method. Single bit DSD digital is input to the FIR filter via delay line, the filter taps (which are the bit-switches) output analog current, all currents are combined by addition to a single analog current that is converted to an analog voltage output. It is an extremely simple filtering system, usually called a Moving Average Filter, or sometimes a Cascaded-Integrator Comb Filter, which is a special type of Moving Average FIR filter very well-suited to decimate or interpolate high speed signals, such as DSD.
Whether one uses HQPlayer for DSD, or one uses the onboard iFI DSD remastering solution, or DSD ‘direct’ conversion, the iDSD PRO is an outstanding DSD playback solution that I would put at the top of my list. (I would not recommend using HQPlayer AND the iFI iDSD remastering engine at the same time however. This will be way too much of a good thing. Purchase the iFI iDSD PRO, experiment with the time limited HQPlayer before you buy it. You can directly compare it to the iFI that way and make your choice.) If you have a large collection of DSD files in your library, the iDSD PRO is a must audition. Even if you don't have a collection of DSD files, the DSD remastering solution could add new life to the sound of your PCM files, as it uses the most simple pathway to analog conversion. It will serve you very, very well. Of course, the native PCM conversion used by the DSD1793 in the iDSD PRO is very unique and a special experience as well. But it's a treat to have both options!
Finally, I would say a few words about the iDSD PRO headphone solution compared to third-party options. I auditioned the iDSD PRO using only headphone outputs. I compared the onboard headphone amplifier output with the iFI ZEN CAN standalone amplifier and the THX technology-based S.M.S.L SP400 standalone headphone amp. There is no doubt the iFI iDSD PRO as a standalone DAC using its primary outputs (indeed it has its own remote for volume control), creates an incredible sound. As a head-fi guy, I must admit my bias though, and say the BEST sound to my ears came from the onboard headphone output. The iDSD headphone amp is designed from the ground up for maximum fidelity as part of the entire system. You will find the appropriate gain for most any headphone on the market with its controls at 0 gain, 9db gain, and 18db gain. Outputs are both single ended and balanced, with the balanced output using a 4.4mm Pentaconn output. Single ended outputs are available via both standard 1/8 inch and 1/4 inch headphone outputs.
The iDSD PRO headphone output may not be able to drive quite as many headphones at the extremes as well as the S.M.S.L SP400, but the majority of headphones are easily drivable by the iDSD PRO, and considering the headphone output is designed in tandem with the Digital to Analog Converter, the overall fidelity is at a level the S.M.S.L cannot match. The ZEN CAN came closer to matching the overall fidelity of the iDSD PRO output, but it couldn’t match the overall dynamic level nor the transient performance of the onboard headphone amp. Unless you have headphones that require more than the output the iDSD PRO can match, I would suggest saving your money and enjoying the excellent sound of the on-board headphone output. If indeed you need a bit more ‘ummph’, the iFI iCAN PRO is an easy suggestion. Click here for more information. Then you will have the very best of both worlds, and one of the very best headphone DAC/amps that the market currently provides. If you can’t afford to add the iCAN PRO, and need more power than the onboard iDSD PRO DAC can provide, then easily recommended without question is the S.M.S.L SP400 THX 888 headphone amp. It is an excellent sounding amp, will drive anything you can throw at it, but it will NOT quite reach the absolute fidelity of the onboard iFI headphone amp, nor the iCAN PRO, which is designed from the ground up as a system. But it makes for an excellent cost effective solution that should bring no shame to the owner whatsoever in the face of competition. It's an outstanding and powerful headphone amp in its own right. But it can't match the overall fidelity of the on-board headamp in the iDSD PRO for a large majority of headphones.
CONCLUSION / MEASUREMENTS
Finally, after many months I have completed my iFi review trifecta. (Click HERE for easy single page access to the review trifecta.)
Reviewed are the iFI ZEN DAC V2, the iFI NEO iDSD, and the most venerable of the three you are currently reading, the iFI iDSD PRO. We have provided an in-depth review of the low, medium and high range of iFi products. We began with the ‘lowly’ in price only iFI ZEN iCAN v2, proceeded to the iFI NEO DAC/headamp, and landed here on the iFI IDSD PRO. (non-Signature version). The full truth be told, no matter what one spends, they will get a truly great product for the money and beyond. (Ahem, slight interjection here. In NO ONE'S quantum universe is the ZEN DAC V2 equal to the iDSD PRO. It just ain't happening. The PRO is priced in a different league with professional features, and deservedly so. At the moment, the iFI iDSD PRO Pentaconn edition is by and far going away as the DAC/headamp to own under $5,000. This might change, however, once I have the chance to review the Signature Edition. iFI? You out there listening and could you send me a demo? Getting on my knees and begging is worth a try??)
The audio fidelity of these products is exceptional. Do you want a product that produces spot on instrument timbre along with fine details that never sound unnatural? iFI products are for you. Are sharp dynamic transients important to you? They are important to iFI as well. Do you prefer the sound of R-2R type DACs? Despite being a quite unique take on a Delta-Sigma DAC, the majority of the sound you hear will mimic a R-2R type DAC due to the DSD1793 chip which converts the most significant 6 bits directly with no Delta-Sigma processing nor any DSP trickery (that is, other than the masterful design that allows for scramble code that will create better linearity that any R-2R DAC that money will likely buy). How about a chipset so flexible that in a moment's notice it also becomes a true analog DSD CIC/Moving Average FIR filter with an 8 bit delay line with scramble code/dynamic element matching?
The Burr-Brown DSD1793 and Burr-Brown chips like it certainly do not get enough credit, likely because they exist in an era when chips like ESS and AKM dominate with their far lower than necessary distortion numbers. Indeed there is more to a chipset than its maximum SINAD. Some will be quite critical of iFI products for ‘only’ having a SINAD in the neighborhood of 100db. Well, that isn't all that surprising considering the DSD1793 chipset is rated right at 100db SINAD by Burr Brown/TI. The Burr Brown segment DACs from the late 1990’s/early 2000's are exceptional sounding chips for their time, and STILL are exceptional sounding chips for our time. Especially in the hands of engineers like Thorsten Loesch who made the DSD1793 get on the floor and dance when its greatest ability at the time was to simply leap in the flower girl's section.
Finally, do you want the iFI version that does all things iFI does well, and then some? The best sounding iFI DAC with Headphone amp, bar none, along with a state of the art studio grade DSD oversampler all the way to DSD1024? As well as accept DXD up to 768khz and DSD1024 natively? (Not just for onboard over-sampling!)
As one might expect, out of all the iFI products reviewed here at Euphonic Review, the iDSD PRO is the winner going away. It will be difficult in our opinion to find any DAC under 5000 USD to exceed its overall sound fidelity, and perhaps impossible to find any DAC/headphone amp combo under 5000 USD, period, that can exceed the iDSD PRO.
Yes, there seemed to be some bugs and issues early on that plagued this model. But as of 2023 this is a very, very mature product that feature-wise keeps up with and audio-wise still exceeds the state-of-the-art.
OUR RATING: (0-10 scale. 8 or higher numbers represent best of industry. For the final score calculation, each category is given a (undisclosed) weighting and is tallied for final score. Although perfect 'fairness' is unlikely, our system tries to be as unbiased as possible.
sound quality: 9.5
build quality: 9.6
ease of use: 9.5
TOTAL RATING: 93.5
The iFI iDSD PRO comes with Euphonic Review’s HIGHEST RECOMMENDATION and is the FIRST recipient of our Editor’s Choice Award.
*Before listing today's measurements, I have some more comments about 'SINAD'. For whatever reason, it has become the measurement 'FAD' of the 2020's. We all know that it is nothing more than THD+N expressed as a positive number. From now on, I will not be providing a 'SINAD' number. This is the final review that will mention SINAD. One can easily ascertain the SINAD from the THD+N number. Furthermore, the insistence of importance tied to SINAD has caused more than one excellent product to be devalued. SINAD is NOT the end all measurement for fidelity. Many a great sounding DAC with only average to good SINAD has suffered needless ridicule from the armchair warriors who likely have never even heard said product.
As one can see above in the DSD1793 Data Sheet, the THD+N is expressed in a percentage. Precisely 0.001%. Conversion to SINAD, this means the DSD1793 chipset is capable of exactly 100db SINAD, which is quite a good measurement. Therefore the SINAD limitations of the iDSD PRO belong to the DSD1793 chip itself, and not to any design flaw of the iDSD PRO.
As previously mentioned, iFI did not choose the DSD1793 chipset for its prodigious SINAD output. It was chosen for its R-2R like performance without the consequence of 'zero-crossing' error prevalent in R-2R DACs. It even allows for 'bit-perfect' PCM reproduction over the top 6 bits that can take advantage of Delta Sigma like linearity and dynamic element matching/scrambling. It is a very unique and capable chip with very good THD+N/SINAD performance. Anything between 90db and 100db SINAD is good performance. Over 100 SINAD is excellent performance. I would consider 80db to 90db SINAD mainstream, fair performance. Below 80db SINAD solid state is moving into the questionable zone, however if the output stage is tube based, you can throw out the expectations and start anew. Tubes and SINAD are not besties, by any means. Therefore, SINAD and Euphonic Review are not besties by any means, either.
Now onto other performance metrics
iFi IDSD PRO 4.4mm Pentaconn Edition firmware version 2.15 JITTER RESULTS
THD= 0.0008% at 1khz , THD+N= 0.001% SOLID STATE MODE. I WOULD TO LIKE TO POINT OUT HERE, THAT AFTER THE ADDITION OF THE E1DA SCALER, THERE ARE SOME NOTEWORTHY CHANGES BE MADE. Total Harmonic Distortion is clarified to be -106db, and Total Harmonic Distortion +Noise is now clarified to be -101db, which of course makes sinad 101db!
Frequency Response SS (from 20hz to 20khz), dB: L -1.11db, +0.02 R -1.11db, + 0.02db
IMD 19khz+20khz: -100.7dB
LINEARITY -100dB: +/- 0.01dB
LINEARITY -115dB: +/- 0.75dB
LINEARITY -117dB +/- -1.5dB