Grimm MU1

Review organized by Marc Loubeau / Prestige Audio Diffusion
Review sample provided by Terrason
Initial Review Sample Serial 13-0.002.016
Second Review Sample Serial 13-0.003.037

Retail price including VAT:
No internal storage: €9.800
Available SSD storage: 2 TB (€350) / 8 TB (€950)
Other storage sizes only on special request

After the Olive 04HD, the AudioAanZee Ultra Flow, Reference Flow, and Reference Flow MkII, the 432 EVO, the Aurender S10 and N10, the Pink Faun 2.16x, the Meridian Sooloos MC200, MD600, MS600, and 818, the Melco N1A/2 and N1ZH/2, the Euphony Buggy/Zotac, the Antipodes DX2, DS, EX, CX, and K50 Music Servers, and twice as many Streamers/Network Players, not to mention various server software and playback applications that I have tried throughout the years, I figured that, by now, surely, there’d be no more large surprises for me. Well, of course, that’s when a new server entered my premises and totally surprised me.

Grimm Audio

Founded in 2004 and based in Eindhoven, the Netherlands, Grimm Audio aims to use the collective forces of the greatest audio minds and to this day, all Grimm Audio products carry the joint insight of well-known scientists in the fields of audio electronics, acoustics, and physics.

The two key figures are Eelco Grimm and Guido Tent, respectively Creative Director and Technical Director of Grimm Audio. Together with a team of software-, electrical-, and mechanical engineers, they produce audio equipment that is refreshingly different while yielding high praise the world over.

Being Dutch myself, I can’t help but feel a little proud:-)

MU1 Backdrop

Designed to complement the Grimm Audio LS1 loudspeaker system, the MU1 has sort of inadvertently taken the audio world by storm. This is in no small amount thanks to the efforts of Ben van Leliveld who was positively raving about the product on every occasion and during every demo that he hosted. Indeed, it was through one of Ben’s demos at the Listening Matters showroom that I first laid eyes on the MU1, at that time combined with Zanden amplification and Kroma Audio loudspeakers. Later, I would hear the MU1 in the role envisioned by the design team, along with the LS1 speakers during one of the last demos at Garmt and Bjorn’s Beter Beeld & Geluid showroom before it closed down. While I was quite impressed with the performance of the MU1+LS1 system performance, it was impossible to pin down how much of this was attributable to the MU1. Up until this point, I’ll be honest and admit that I thought it was mostly hype, possibly even more so when Ben proclaimed the MU1 to be The One server worthy to sell your CD player for.

It wasn’t until a close friend and fellow audio reviewer obtained a MU1 for his review reference system that I really took notice. Like me, he had a hard time finding the ideal Music Server to work alongside his treasured CD player. We both feel that computer-based audio has made large strides but, somehow, still lags behind a good CD player in certain aspects. To be fair, if the CD player is of insufficient quality, it can also be the other way around, in many aspects, at least. Overall, though, there is something to CD playback that is less mechanical and stilted than any music server or streamer replay. Excuse me for not going into detail on this perception, as I’ve rambled on about this more than enough in my other Music Server reviews.

Anyway, in his quest to find the ideal Music Server, the friend auditioned the best servers and streamers that are currently available and since I had already been doing the same thing for over a decade, we decided to join forces and compare the best of the best. I went over there with my Antipodes K50 and my accumulated knowledge and, well, let’s say that I was in for a surprise.

MU1 Description

With the MU1, the goal was to set a new benchmark in music player design, not only in terms of sophistication but also in terms of sound quality. Grimm Audio selected Roon for the user interface and the associated audio engine for file- and stream playback. An alternative User Interface and audio engine will be added later. Music can be sourced from streaming services such as Qobuz and Tidal as well as from an external NAS or a USB thumb drive. Streaming from Qobuz sounds superb and in many cases identical to local playback. Local music can be added to an internal SSD that can be ordered in a 2TB or 8TB size.

Powered by a twin-PCB switching power supply developed in-house to provide the lowest possible jitter values, the MU1’s core is shaped by a NUC board that runs Linux and the Roon Core server component. Importantly, Grimm does not just rely on standard Linux or Roon packages. Refusing to use standard libraries, the Grimm team wrote their own code from the ground up. This is where the MU1 differs from other music servers and likely an important reason for why it sounds so superb.

Arguably, the actual core of the MU1 is its custom-designed FPGA interface board. Whereas many competing products use standard oscillators for FPGAs, Grimm uses a very high-quality Tentlabs oscillator for this task while using an ultra-low jitter proprietary Grimm audio oscillator as the main audio clock. The Grimm clock and associated circuitry are encapsulated in a fully shielded box.

It’s on this FPGA board where the MU1’s magic happens, with the FPGA interface accepting all file formats and sample rates from Roon in their native formats and converting them with a user-defined fixed multiplier (2x or 4x) using a “Pure Nyquist” decimation filter. The resulting signal is available on the rear via two AES/EBU outputs and an RJ45 output that is dedicated to the LS1 speaker system. The MU1 can also be used to stream to other Roon endpoints but, naturally, this bypasses the FPGA board and its beneficial processing.

The MU1 plays all the file formats that Roon supports, such as WAV and FLAC, and it has native support of PCM formats up to 8x the base rate (8FS or “DXD”) and of DSD formats up to DSD256. The FPGA processor will upsample 1FS and 2FS sources to 4FS and it will downsample 8FS and DSD or DXD formats to 4FS. In other words, there is no fixed sample rate and the used rate depends on the input rate. For instance, 44.1kHz will be output as 176.4, and 48kHz will be output as 192kHz while 96kHz will also be output as 192kHz. An input signal of 192kHz remains unchanged while higher sample rates will be downsampled.

While I can understand there may be those who object to the notion of oversampling and insisting on retaining the purity of the original signal, it’s worth noting that the vast majority of CD players and DAC’s have a built-in oversampling that is usually 4FS. Even the earliest Philips players, including those with 14-bit DACs, used fourfold oversampling. With that out of the way, the downsampling of very high sample rate source material might still sound strange but there’s a very simple explanation for this. It is the maximum rate that AES3 or S/PDIF will support. The Grimm Audio team performed elaborate tests and has concluded that the clock accuracy (low jitter) is much more important for the audible results than an even higher PCM sample rate or even DSD.

To make the magic of the FPGA board more widely available, the MU1 can also accept external inputs on AES/EBU and S/PDIF on cinch and TOSlink, and process these just like it does the internal Roon signal.

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