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Resonessence Labs Concero HP & Concero HD in review

  • The HRT microStreamer is a close-to-ideal portable headphone/DAC solution. It’s small enough for planes, trains and automobiles. Better still, it plays nicely with Apple’s iPad (coverage of which will arrive sometime in October). However, this pocket-rocket has two ‘limitations’: 1) it’s a bit thin/spindly-sounding with my favourite budget headphones, the AKG K-702 and 2) it can’t decode PCM sample rates above 96kHz or DSD. Neither of these are unreasonable shortcomings at the $200 price point but in order to vanquish one or both we need to push upfield.

    Last week I spent some time in a quiet beachside village on the Central Coast (an hour north of Sydney). Relaxing on the balcony and overlooking the ocean, my self-imposed audiophile brief was to maintain the portability of the HRT headphone amplifier (USB bus power only) but improve grunt and snarl for the AKGs as well as find something better spec’d with which to spin DSD. G’day Resonessence Labs Concero HP (CA$850).


    In for a penny, in for a pound. Released alongside the DAC/head-amping Concero HP is the DAC-only Concero HD (CA$850). That would later see a spin back at home, tethered to Burson’s superb HA-160 and the aforementioned AKGs. How would these new Conceros stack up against the original (CA$590, review here)? There’s a lot of technical nitty gritty to get through as well as some musings on the HD and HP’s most prominent new feature – DSD/DXD decoding – so strap yourself in…

    The USB input implementation on both Concero HP and Concero HD remains the same as the original model – a design trickled down from Resonessence Labs’ flagship INVICTA DAC (CA$4995). It comprises custom (FPGA) DSP code and a Cypress Semiconductors CY7C68013A chip. The code handles the up-sampling, the Human Interface Device (HID) control of the host computer (more on which in a moment) and asynchronous control of the USB data pipe, including the all-important jitter rejection.

    “We spent a lot of time making sure that speed differences between the host PC’s reference clock and the high quality low phase noise reference of the CONCERO (and INVICTA) didn’t cause issues. The async code needs to be able to handle when the host PC is both too fast and too slow. We made the CONCERO and INVICTA code work for up to +-4000ppm. To allow for this large difference we needed a custom solution with larger data buffers. Having these buffers also makes our solution less likely to dropout when there are other USB devices connected to the host PC.”, says RL mainman Mark Mallinson.

    The custom FPGA code is field upgradeable. End users of all Concero models can download and run the Concero Updater app [Mac or PC]. A single click installs new firmware on the device. Readers of the future take note: I ran firmware 2.3.0 on all three Concero units during this review assignment (August/September 2013).


    Human Interface Device (HID). Every Concero can ‘talk’ to its host computer by relaying Apple remote signals of play/pause and previous/next. The HP version goes one better: a turn of its infinite rotary appears to attenuate the host PC’s system volume…but it doesn’t, not in the traditional sense. These system volume changes send signals back to the Concero HP so that its 32-bit Sabre DAC chip executes the volume scaling. This coding stunt also works with some music player apps too: when selected as the active application, I could see Audirvana+’s rotary respond to turns of the hardware pot on the Concero HP, whilst all-the-time knowing I was completely dodging software volume attenuation. Of course, I could still apply mouse control to Audirvana+’s volume dial directly should I so wish, according to which the majority of my listening took place between -14db and -17db. Hardware and/or software control means the best of both worlds – very clever.

    Here’s an explanation on how the 32-bit digital volume attenuation works on the HP and HD:

    “The volume control is done completely in the 32-bit domain, meaning that the input source is first extended to 32-bits and 32-bit precision is used all of the way through. What that means is if you set the volume control anywhere from 0 to -48dB, all the original dynamic range of the 24bit input is preserved. Once the volume is lowered below -48dB, you will start to throw away some of the LSB’s. Note that for 16 bit signals its -96dB where the original bits start to get discarded.” [Source: Resonessence Labs website)


    The in-house designed up-sampling filters found on the original Concero are also present in the HP and HD versions. The HD box requires an Apple remote to click through filters one by one whilst users of the HP unit can cycle through them with a single press of the volume pot: no-upsampling (bit-perfect), Minimum Phase IIR (4x) and Apodizing (4x). On the HP and HD models I still prefer the IIR filter with Redbook source material – it’s altogether smoother, a copacetic match for AKG K-702’s drier vibe, adding a shade more depth into the bargain. Warmer/darker headphones might benefit from the steelier edge of the Apodizing filter.

    Note: these filters only kick into action when the Concero HP/HD see 44.1kHz and 48kHz sample rates. Hi-res gets passed through bit-perfectly.

    Note also: You don’t get the volume drop when engaging the filters on the HD and HP units (as you do on the original).

    See that coaxial connection on the rear? It does double duty as input and output. Connect the Concero HD to a PC or MAC (as per normal headphone listening) and the S/PDIF connection behaves as an output. Yes, it’s a USB-S/PDIF converter! I found the original Concero to be on par with – but more fluid than – the hitherto budget class-leading Audiophilleo 2. The original Concero remains my go to USB-S/PDIF converter (with Wyred4Sound’s µLink pulling up a close second). I found nothing in the new HD model to dissuade me from this conclusion; that the original Concero (via firmware update) can match the HD’s ability to hand-off DSD64 (1x) from USB input to S/PDIF output will be good news for both existing and prospective owners. If you’re intending to bridge DSD64 in this way you should check out this DSD database to ensure your DAC can accept DSD64 on its S/PDIF input(s).


    To get the Concero HD (note: not HP!) to accept a S/PDIF input its USB port must either be connected to a power-only USB device (e.g. 5V wall-wart) OR connected to a host computer where two, short upward clicks of the Apple remote are then required to turn off the USB data input in favour of the desired S/PDIF input stream. When in S/PDIF input mode, incoming data is sent to the FPGA for the S/PDIF decode, after which the signal is passed onto the DAC chip.

    The Concero HP requires a little more user intervention for S/PDIF in/out selection. Its configuration utility – coming soon to the RL website – allows one to set the S/PDIF to input OR output; this can be changed as often as the user requires.

    Let the chips fall as they may. They might all look alike but both the HP and HD models internally differ from the original. The latter runs a 24-bit ES9023 chip whilst the newbies make use of ESS Labs’ latest silicon: the ES9018-2M, intended for smartphones, tablets, digital audio players and other mobile devices. It’s a 32-bit Sabre chip, closely related to the ES9018 (found in more luxuriou$ DACs). However, the ES9018-2M’s output stage doesn’t have an integrated op-amp (found inside the ES9023) so the Concero HP and HD both enjoy the off-board output staging of an AD8397 op-amp. These changes go some way to explaining why the HP/HD versions attract a CA$250 premium.


    The ES9018-2M chip also gives the Concero HP/HD an advantage over its forerunner: an ability to decode DSD64 and DSD128 (via the DoP protocol) as well as DXD (aka 24bit/352.8kHz PCM). The original Concero’s ES9023 DAC won’t decode DSD but it offers a PCM ceiling that goes higher than either of the HD and HP units: 24bit/384kHz.  This wafer-thin advantage will hold until RL’s engineers resolve the 384kHz distortion issue troubling the two newer models.

    Show me the money. Despite a paucity of mainstream titles, DSD is a hot ticket amongst audiophile consumers. Demand for DSD-capable DACs has strengthened during the last year or so. Lest anyone sees my coverage of DSD-related products as proof positive that I’ve gone gaga for the DSD format, let me be abundantly clear: I haven’t.

    In the three years since my initial interest in hi-res digital audio my song library hasn’t been overrun by über PCM releases. I’ve bought all the R.E.M., Talking Heads, Joy Division and Rolling Stones on offer at HDTracks but I still have only a hundred or so hi-res releases sitting inside iTunes. Compare that to tens of thousands of Redbook/CD rips sitting in my library. Playing the numbers game, Redbook resolutely remains the main course with hi-res PCM being an interesting side dish and DSD a small-but-pleasing dessert.

    Maybe Chad Kassem can build inroads to the major labels faster than HDTracks’ David and Norman Chesky. Maybe.’s DSD catalogue stands at 114 titles (at time of writing), but like HDTracks, it’s (technically) US only – a sharp reminder that overseas licensing deals are a legal quagmire. Having recently renewed their hi-res vows, Sony may be able to pull off wider distribution deals but I’m sure I’m not alone in my reluctance to buy into a format on the promise of future riches. I’m not sold…yet. Not until the number of available DSD downloads improves significantly.


    “But what about the music offered by Blue Coast, 2L et al?”. Sorry guys, it sounds wonderful but it ‘says nothing to me about my life’ (Remember: You are a DJ – you are what you play). As one reader opined in the comments section of this week’s Schiit Loki news piece: “…the library of available titles [at] looks like my Aunt Virginia’s record collection (5 or 6 Norah Jones records and a bunch of 30′s to 50′s jazz)”. Ha!

    For the time being, I’m staying pragmatic. With my reviewer hat on, I’m keeping one foot in DSD waters and one on dry land to temper the tide of (over?)-enthusiasm. I listen to music (primarily) because I like it and not (just) because it sounds good. Otherwise Arcade Fire would never get a look in. To invert those priorities – to put sound quality ahead of emotional nourishment or sing-a-long enjoyment – would see the tail wagging the dog. I’m not that kind of audiophile.

    Thankfully, Depeche Mode’s Exciter ticks both boxes. It’s my favourite DM album and Mark Bell’s techno-tinged production means it sounds bloody marvellous (exciting!), even if it isn’t the last word in dynamic range.


    Credit where it’s due. DSD and Depeche Mode seem made for each other. The electronic squiggles and bleeps that Bell has baked deep into the mix are easier to discern on the SACD rip (DSD) than a CD rip (ALAC) of the same 2007 remaster. Via the Concero HP, the DSD ups the jump factor, is less condensed and more munificent.

    Bandwidth and storage issues associated with DSD aren’t insignificant either. The aforementioned SACD rip of Exciter consumes 2.5Gb of storage space. Storage might be cheap but how long does it take YOU to download 2.5Gb? How many releases could you grab per monthly download quota?


    With the Concero HD running into a Burson HA-160 and driving the AKG K-702 headphones, this year’s remaster of Bob Dylan’s Self Portrait sounded deliriously well defined and expertly balanced. Yes, I’d describe the presentation as abundant with resolution – great for digging out textural information found deep within the recording – but it’s resolution that isn’t too deeply carved or dry at the edges. These are the qualities that made the original Concero so enjoyable and rarely fatiguing. How much of this composite sound is attributable to the Burson headphone amplifier though?

    The answer came from pitting the solo-running Concero HP against the Concero HD and Burson HA-160 combo. The HP proved to be tighter, more present, transients were keener, bass leaner, an overall more exciting presentation, channels not quite as well separated. The Burson HA-160 counterbalances the HD with a mellower vibe (which I prefer) but you can’t take it on the road. The Burson doesn’t run on USB bus power and therefore has none of the Concero HP’s go-anywhere appeal. To return to where we came in, the Concero HP is fuller-bodied and more dynamic with the AKG K-702 than the HRT microStreamer.

    This echoes my recent conclusions where these same two portable DAC/head-amps were pitted against the Astell&Kern AK120 (in USB DAC mode) with KEF’s more easily driven M500 headphones. The Astell&Kern AK120 in USB DAC mode offers a softer, more narrow-eyed presentation than the Concero HP but the AK120 can only decode DSD files hosted on the device itself. It isn’t (yet) a DSD-capable USB DAC.


    Allow me to quash some misty-eyed nostalgia while we’re at it: the Concero HP’s ability to properly juice the K-702 is light years ahead of the classic NAD 3020i (fed by the Concero HD).  Like so many headphone stages dropped into integrated amps, the NAD sounds scrawny and malnourished with the Austrian-made cans. A great big “NO!”.

    Nothing seems too complicated for the HP: as well as the propulsive Depeche Mode DSD, Radiohead’s super-dense “Jigsaw Falling Into Place” is cleanly sliced and diced.  The acoustic guitar that fleshes out the song’s core isn’t lost in the mix – it hovers above the surface. Such separation isn’t communicated by lesser able decoders.

    Clearly the Concero HP is a portable headphone rig for bench-top or balcony listening – where size/weight isn’t quite as paramount as it is down on the beach. The Concero HP is a great choice; and not simply because there’s currently almost zero competition in the portable, DSD-USB DAC/headphone space. That on-paper advantage won’t last for long. Light Harmonic’s Kickstarted GEEK DAC drops it drawers in January 2014 but Resonessence Labs’s own thumb-sized Herus DSD-USB DAC is just around the corner too (but that’s a story for another day).


    Good old original vs. new and improved. With HD and original Concero stacked one on top of t’other, a direct comparison was a cinch, revealing the HD unit to be more lit-up, more up-in-your-grill and a more eager to get its message across. This delta wasn’t insignificant.  The HD shares the HP’s tighter-brighter energy-drink sensation.  Don’t think ‘bright’, think ‘spicy’ and ‘incisive’. If you don’t need DSD playback or if your system is already well caffeinated, stick with the original Concero – you’ll save CA$250 and take home a sound that’s a little softer, one that reveals more connective tissue between musical players. If separation and crispness are your priorities, the Concero HD is your guy.

    If you’re ready to commit to DSD, you’d be hard-pressed to beat the Concero HD’s combination of detail dig, it-is-here presence and price; no mean feat considering it relies on (noisier) USB power and the majority of the immediate DSD DAC competition doesn’t. Again, Resonessence Labs’ portability edge  shows sharper teeth to rivals from the likes of TEAC UD-501 (US$850) . The Concero HD doesn’t present as smooth or as rich as a FireWire connected, mains-powered Mytek Stereo192-DSD DAC (US$1595, review here)…BUT the Concero HP’s headphone staging is easily the match of that built into the Mytek DAC – a conclusion that arrives on the back of predominantly Redbook listening. How’s that for irony?


    Final thoughts. What I like most about the Concero range is each model’s multi-purpose functionality.  No USB?  No worries. All models take a S/PDIF input for CD player or streamer box amelioration.  Turning that input into an output means all models double up as superb USB-S/PDIF converters; RL’s in-house coded jitter rejection appears to be extremely effective down on the ground. Custom filters bring us three subtle gradations in flavour and remote control is taken care of by an Apple remote.  Above all that, Mark Mallinson and his team should be heartily congratulated for the features and sound quality they’ve conjured from the USB 5V-power pipe – BRAVO.

    [Footnote: cabling a quarter inch jack to twin RCAs could see the Concero HP serve time as an entry-level digital pre-amp.  Hmmmmm……now there’s a thought.]


    Associated Equipment

    • QED Profile USB cable
    • WireWorld Starlight USB cable
    • Light Harmonic LightSpeed USB cable <— this thing is superb!
    • HRT microStreamer
    • Astell&Kern AK120
    • Burson HA-160
    • Resonessence Concero (original)
    • Zu Audio Mission interconnect(s)
    • AKG K-702


    Audition Music

    • Depeche Mode – Exciter (2007 remaster), Redbook PCM and DSD
    • Various Artists – Sci.Fi.Hi.Fi Vol.3, Mixed by Alex Smoke (2006)
    • Bob Dylan – Self Portrait (2013 remaster)
    • Radiohead – In Rainbows (2007)
    • David Byrne & Brian Eno – My Life In The Bush Of Ghosts (1981)
    • Aphex Twin – …I Care Because You Do (1995)


    Further information

    Written by John

    John currently lives in Berlin where he creates videos and podcasts for Darko.Audio. He has previously contributed to 6moons, TONEAudio, AudioStream and Stereophile.

    Darko.Audio is a member of EISA.

    Follow John on YouTube or Instagram

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