iFi audio Pro iDSD 4.4 DAC/Headphone Amplifier/Streamer Reviewed

Chris Martens says the iFi Pro iDSD 4.4 delivers the richest mix of audiophile-oriented features and functions of any DAC/headphone amp/streamer near its size or price.

iFi audio Pro iDSD 4.4 DAC/Headphone Amplifier/Streamer Reviewed

By Author: Chris Martens
Chris Martens has been an avid audio enthusiast for more than 50 years and has been an audio journalist for the past 18 years. His CV includes: Senior writer for The Absolute Sound, Audio Editor and later Editor for The Perfect Vision, founding Editor/Publisher of AVguide.com, founding Editor of Playback, Publisher and Senior Writer for Hi-Fi+, and Editor of Hi-Fi+/The Absolute Sound Ultimate Headphone Guide.

iFi audio is a British manufacturer of affordable and physically compact high-performance audio products, many of which are targeted toward high-end personal audio enthusiasts. Unlike many personal audio manufacturers, however, iFi has deep roots in the world of traditional high-end audio as it is a spinoff from and subsidiary of Abbingdon Music Research, a well-regarded British builder of top-tier audio electronics components. The firms share common management and product development teams headed by Managing Director Vincent Luke and Chief Technology Officer Thorsten Loesch, respectively.

ifi-idsd-5-610x397.jpgFrom the beginning, the concept behind iFi audio was to create accessible audio components whose sound and overall performance would closely mirror the capabilities of AMR's top-tier offerings but for a fraction of the price. This review focuses on the latest version of iFi's flagship DAC/headphone amplifier/digital preamplifier/streamer, the Pro iDSD 4.4 ($2,749 at Crutchfield and Amazon).

By audiophile standards, where large and ostentatiously styled components seem to be the norm, iFi's Pro iDSD 4.4 arrives in an attractive but modest and diminutive half rack-width chassis with a Wi-Fi whip antenna sprouting out the back.

The Pro iDSD 4.4 is actually iFi's second-generation version of the Pro iDSD, and it got its name by substituting a 4.4mm Pentaconn-type balanced output headphone jack for the 2.5mm balanced mini-jack used in the original Pro iDSD. With the advent of the Pro iDSD 4.4, iFi also added MQA decoding capabilities.

The Pro iDSD offers three user-selectable digital audio processing modes: Direct -- Bit-Perfect (a non-upsampling mode where neither PCM nor DSD signals are processed in any way); DSD -- Remastering (where all incoming PCM or DSD signals, save for DSD512 signals, are converted to the user's choice of DSD512 or DSD1024 for playback); and PCM -- Upsampling (where PCM signals are up-converted to 705.6kHz or 768kHz and processed through the user's choice of five digital filters).

The Pro iDSD supports a wide range of digital audio inputs, some of which require use of the readily available MUZO Player app. Inputs include: Ethernet, Source Host USB 'Type A' (for connecting external hard disk drives, USB memory sticks, or similar storage devices), DAC USB 'Type B' (for connecting a PC host such as a laptop or server), Coaxial/Digital, microSDHC, AES/EBU (XLR) digital input, Wi-Fi antenna (for connection the Pro iDSD to a local WiFi system and then using the MUZO app to stream Spotify, TIDAL, Napster, QQ Music, and other content sources), and a multipurpose BNC digital input (for use either as an S/PDIF digital audio input from high-end source components or as an AES3id clock synchronization input). All inputs (including USB) feature galvanic isolation.

PRO_iDSDiCANiESL_-15.jpgAt the heart of the Pro iDSD DAC section are four interleaved, 64-element, bit-perfect DSD and DXD DAC devices sourced from Burr-Brown. A second-generation XMOS XU216 X-Core 200 Series 16-core processor capable of a whopping two billion instructions per second is used to support the Pro iDSD 4.4's USB interface and to handle decoding of audio data from all inputs. A Crysopeia FPGA (field programmable gate array) engine handles all digital filtering and PCM-to-DSD remastering tasks, up to DSD1024 levels. The iFi design team states that the X-Core processor is best optimized for USB audio and signal-decoding tasks, whereas the Crysopeia FPGA is better suited for "...upsampling and digital filtering duties."

The amplifier section of the Pro iDSD 4.4 features three user selectable output stage options. The first option, Solid-State, provides a fully discrete, J-FET based, Class A circuit. The second option, Tube, switches from the J-FET solid-state circuit to an all-tube Class A circuit based on a pair of NOS (new old stock) GE5670 tubes. The third option, Tube+, is basically a variation on the second, where the same Class A, dual GE5670 circuit is used, but with negative feedback reduced, which allows "a greater amount of the tubes' natural harmonic distortion" to be heard. Three user selectable levels of master gain -- 0dB/9dB/18dB -- can be applied for any of the unit's three output stage options.

The Hookup
Both balanced and single-ended analog outputs are provided on the Pro iDSD 4.4's faceplate and rear panel. Up front, there are three headphone output jacks (6.3mm single-ended, 3.5mm single-ended, and 4.4mm balanced). Out back there are two sets of stereo analog outputs: balanced (via 3-pin XLR connectors) and single-ended (via RCA jacks).

Since its name implies the Pro iDSD 4.4 can be used for pro sound applications, the rear panel provides a small rotary output mode selector switch offering four choices: HiFi fixed (for using the unit purely as DAC in a hi-fi system), HiFi variable (for using the unit as a digital preamplifier), Pro fixed (for using the unit as a DAC in pro sound applications), and Pro variable (for using the unit as a digital preamplifier in pro sound applications). The difference between the HiFi and Pro settings is that HiFi fixed mode outputs are set at a maximum of ~4.6V, where Pro fixed mode outputs are set at a maximum of ~11.2V (in keeping with studio norms).


Faceplate controls include a master On/Off switch; a color-coded status light (shaped like the iFi logo); a round porthole-type OLED display that indicates the unit's operational status and settings; a master gain selector switch; an output mode switch; a rotary/press control knob for selecting inputs, controlling the unit's absolute polarity, and regulating display brightness; a rotary/press control knob for selecting preferred PCM filters, invoking DSD remastering functions, and a WPS switch to facilitate pairing between the Pro iDSD 4.4 and a router; an IR window for use with the included minimalist remote control; and a rotary volume level knob connected to a high-quality multichannel ALPS volume control that regulates output from both the headphone jacks and the rear panel analog outputs (when variable output modes are selected).


For my listening tests I used the Pro iDSD 4.4 at the heart of my all-iFi personal audio reference system. The system consists of the Pro iDSD 4.4 as the central source component, the Pro iCAN balanced output tube/solid-state headphone amplifier, and the Pro iESL electrostatic headphone step-up device with variable electrostatic bias voltage outputs. Together, these three iFi components function as an excellent do-all personal audio reference stack capable of driving high- and low-sensitivity full-size dynamic headphones, electrostatic headphones, high- and low-sensitivity universal-fit earphones, and custom in-ear monitors.

Pro-iDSD-Pro-iCAN-2-1.jpgDigital audio signals are fed to the Pro iDSD 4.4 via an oldie-but-goodie AURALiC ARIES wireless digital bridge, which is equipped with a large, USB music library hard drive. All audio files passed through the ARIES are of CD-or-better quality, representing a mix of 44.1/16- or higher-resolution PCM and DXD files, and DSD64-or-better DSD files.

Reference headphones on hand for this test included four high-performance planar magnetic models: the Dan Clark Audio ETHER 2, the Final D8000, the HiFiMAN Susvara, and the Meze Empyrean. I also had on hand a range of high-quality earphones and custom in-ear monitors, including the Westone ES80 and ES60 CIEMs, and the Campfire Audio Solaris and Andromeda universal fit earphones.

With many products, it's possible to frame a reasonably concise yet detailed description of the unit's quintessential sound, but with the Pro iDSD 4.4, the descriptive task is complicated by the fact that the unit offers so many input, processing, upscaling, filtering, and amplification options. That, of course, is the beauty of the thing. It's a device that gives you all the tools you need to answer some fairly deep audio questions.

For example, the Pro iDSD 4.4 lets you ask and answer these questions:

  • What, if anything, is the sonic effect of changing the unit's absolute output polarity?
  • Would a given PCM audio file sound better if upscaled to 705.6 or 768kHz levels?
  • Would a given PCM audio file sound better if remastered in DSD format?
  • Would a given DSD audio file sound better if upsampled to DSD512 or DSD1024?
  • What, if any, sonic effects do various digital filters have?
  • For any given headphone or earphone, what master-gain level sounds best: 0dB, 9dB, or 18dB?
  • Do all digital audio inputs sound pretty much the same, or are there qualitative differences between them?
  • Does switching between single-ended and balanced output have much impact on the sound?

The point is that the Pro iDSD 4.4 stands as an open invitation to explore and find your own optimal sound, which often will vary from one listener to another.

My comments above notwithstanding, I do think it is possible to identify some consistent, underlying elements of the Pro iDSD 4.4's core sound.

First, the Pro iDSD 4.4 offers what I would call natural, organic warmth. This does not mean that it is a cloying, honey-toned device, but it does mean that it steers well clear of the sorts of cold, sterile, analytical-sounding presentations that afflict some DACs and headphone amps. If you focus on string tones, and especially the tonality of a solo violin, you will discover the Pro iDSD 4.4 at once captures both the incisiveness and also the subtle sweetness of the instrument. A great example would be the sound of the Pro iDSD 4.4 on violinist Hilary Hahn's recording of the Meyer Violin Concerto. On this beautiful concerto, the Pro iDSD 4.4 deftly reveals the sheer dexterity and clarity of Hahn's performance, while subtly capturing her violin's warmer, more woody-sounding undertones. It's simply beautiful.

Violin Concerto: I. Romanza

Second, the Pro iDSD 4.4 is blessed with considerable resolution and detail, though not in an exaggerated way. To appreciate what I mean, listen to French-Canadian vocalist Anne Bisson's performance of Pink Floyd's classic "Us and Them" from her album Portraits and Perfumes. Bisson's voice is capable of everything from light, articulate, and subtly inflected tones all the way through to a far more robust, throaty, and emotionally charged sound.

"Us and Them" shows the singer venturing to both extremes and all points in between. At each step along the way, the Pro iDSD 4.4 tracks precisely with the expressiveness of Bisson's voice, in the process flexing serious dynamic muscle and diving deep to retrieve even the subtlest shifts in textures and timbres. The accompanists on the track also are also recorded with exceptional resolution and attention to dynamic shadings of all kinds, as the Pro iDSD 4.4 makes abundantly clear (a brief instrument break in the song sounds flat-out terrific).

Third, the Pro iDSD 4.4 does a tremendous job with imaging and spatial details, as well as other soundstaging cues in the music. An ideal illustration would be the track "Nublado" from Será una Noche's eponymous album. "Nublado" is a dark, seductive, almost hypnotic instrumental tango performed by the Argentine Será una Noche ensemble (led by percussionist Santiago Vazquez) and recorded in the small, reverberant sanctuary of the Gandara Monastero church located about two hours outside of Buenos Aires.

This might well be one of the most magical recordings in my library, and what makes it so are the rich textures and tonal colors of the acoustic instruments in play, the elusive sound of the air surrounding each instrument, and especially the mix of reverberant sounds that show the interactions between the instruments and the recording space. To say this is a highly three-dimensional recording is putting things mildly, and the Pro iDSD 4.4 does that dimensionality full justice.

Nublado - Será Una Noche

There really is no one best sound for the Pro iDSD 4.4, but I can offer some generalizations. On the whole, I found PCM files benefitted from the iFi's upscaling capabilities, and as a general rule I preferred the Gibbs Transient Optimized digital filter on most recordings, most of the time. With that said, though, each of the filters can be useful/beneficial, depending upon the specific recording in play. DSD remastering proved eye-opening in many cases, seeming to enhance dimensionality, harmonic richness, and smoothness, though with perhaps a slight diminution of edge definition on hard, sharp transients. As for amplification options, I found the Pro iDSD 4.4 made sonic distinctions between the Solid-State, Tube, and Tube+ circuits much easier to discern than was the case with the first-generation Pro iDSD.

As far a power output goes, the Pro iDSD can drive even the exceedingly power-hungry HiFiMAN Susvara headphone (sensitivity 83dB @ 1 mW), yet is also quiet enough to work well with ultra-sensitive custom in-ear monitors such as the Westone ES60 (sensitivity 118dB @ 1 mW). Although the sonic differences were subtle, I found the Pro iDSD 4.4 offered lower noise and better presentation of low-level sonic details than the first generation Pro iDSD.

The Downside
There really are no downsides with the Pro iDSD 4.4, apart from the fact that its sheer versatility makes it an inherently complex product. Let's put it this way: The Pro iDSD 4.4's manual is one you will want to read carefully and refer to often as you climb the iFi's learning curve. Bear in mind, the Pro iDSD 4.4 offers three core digital processing modes, extensive PCM upscaling options, powerful DSD remastering options, five digital filters, three amplifier operating modes, and a wide range of digital inputs -- all of which interact with one another to some degree. That's a lot of permutations and combinations to track, so take your time, listen carefully, and enjoy the sonic experimentation.

Comparison and Competition

Apart from iFi's first-generation Pro iDSD, I can think of three competitors that invite comparison with the Pro iDSD 4.4: The $2,999 Mytek Brooklyn Bridge DAC/headphone amp/preamplifier/streamer from Poland, the $2,779 Prism Sound Callia DAC/headphone amp/preamplifier from the UK, and the $1,999 RME Audio ADI-2 Pro FS R Black Edition DAC/ADC/headphone amp/preamplifier from Germany.

All three are roughly similar in that they offer PCM/DSD-capable DACs and strong headphone amplifiers, yet they each offer certain features that differentiate them from the iFi. The Mytek, for example, offers an analog input that can be configured as an MC/MM phono stage. The Prism Sound offers separate output level control for headphones and its preamp outputs. The RME, like the Mytek, offers an analog input and stands as the only unit with both high-resolution DAC and ADC capabilities.

Sonically, each of these three competitors shades more in the direction of the analytical sonic presentation favored by many in the pro sound community, whereas my take is that the iFi offers the richer, rounder, more musically engaging presentation prized by many audiophiles.

iFi's Pro iDSD 4.4 offers the richest mix of audiophile-oriented features and functions of any DAC/headphone amp/preamp/streamer near its size or price. I have chosen it for use in my personal audio reference system partly because it's a really useful and versatile tool, but mostly because I can count on it to help my favorite transducers sound their best.

Additional Resources
Visit the iFi website for more information.
iFi Introduces nano iDSD Black Label DAC/Headphone Amplifier at HomeTheaterReview.com.
• Visit our Digital to Analog Converter category page to read reviews of similar products.

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