Grimm Audio MU1 Music Server | REVIEW











The Grimm Audio MU1 (website) is an idiosyncratic product. This is not a term I typically associate with music servers or digital sources—the truth of the matter is that most of them are simple devices. They use Roon or some other software to manage digital streaming services and files and they send music files to digital converters. Hard to mess that up, right?

Words and Photos by Grover Neville

Wrong. While power supplies and other increasingly subtle tweaks regarding how the digital signal gets to the DAC are not beyond my personal realm of expertise—keep an eye out for a piece on an interesting Innuos piece coming soon—I do also know quite a bit about signal transmission and filters. I had an extensive discussion with Eelco Grimm shortly after receiving this piece, and the main thrust of our discussion, though not about the MU1 specifically, involved digital filtering.

I want to first mention however that my discussion with Eelco was simultaneously refreshing and challenging. Additionally, I probably ought to mention here that if “value” or “affordable” is amongst the words you find yourself using to describe your audio shopping habits, you may be disappointed. If “perfection” (and the pursuit thereof) or “cost-no-object” are phrases that you identify with however, read on.

Although my conversation with Eelco didn’t involve any of these words, the prices Grimm Audio is asking for their equipment speaks volumes. Grimm as a product company has deep roots in pro audio, with Eelco himself having quite a bit of experience in pro audio as well as recording pedigree and talent within the company. Our conversation was wide-ranging and quite fun, and I hope to get a listen to other Grimm Audio products someday.

Regarding the Grimm Audio MU1, our discussions centered around one central point, which was essentially that this is a very straightforward music server. You plug it in, it sends audio to your DAC. Via USB, optical or any other transmission method, this is fairly standard, though the power supply in the MU1 is made of exceptionally premium parts. Where it gets interesting is the AES outputs’ filter.

I’ll try not to bore you with too many technical details, but suffice to say that resampling is a fairly sophisticated and complex science requiring lots of CPU, and well-tuned filters. The process of turning 44.1khz into 96khz or 192khz is nontrivial, and although it may seem simple, to do it well and with the best sound quality actually requires quite a bit of processing power. Many fussy mastering engineers will actually render it at less than realtime speeds to achieve best results, in iZotope RX and some even more obscure programs.

A key element of resampling is the reconstruction filter, and many of you will be familiar with talk of reconstruction filters and up or oversampling as it relates to DAC technology. Aliasing, pre and post-ringing, phase shift, IIR vs. FIR, windowing and buffer size, latency… blah-blah-blah. I know, it would make my eyes glaze over if I wasn’t a complete nerd either. Suffice to say that in my wide-ranging and informative conversation with Eelco, he demonstrated a very sophisticated knowledge of all these technical points, and the Grimm website contains a concise and well written article about their Pure Nyquist Filters.

While the article doesn’t go into particularly great detail about how the filters are constructed or what they look like, the basic gist is that low jitter and high-power CPU are needed for accurate resampling to occur. The jitter problem requires sophisticated clock design, which the Grimm Audio MU1 provides for via its S/PDIF and AES outputs, and the filter requires a dedicated and custom-programmed FPGA, which outputs via the AES connection on the MU1. Grimm has gone to great lengths to customize and code their own chip, and its capabilities are far in advance of a typical Sharc DSP or off the shelf chip—they’re also atrociously expensive to develop.

To keep the technical Jabberwocky speech to a minimum, the Grimm Audio MU1 via its AES output is basically taking over the initial oversampling of the music from the DACs input, as it is equipped with much greater CPU resources and what Grimm believe is a superior filter. Although details on what this filter entails were scarce, Eelco did mention several times that he felt analog artifacts were less perceptually unpleasant than digital and that this was a key factor during the development of this unit. It’s clear he’s a well-reasoned listener who takes the best of subjective and objective findings and is deeply interested in and capable of understanding the technical aspects and their relationship to our perceptual experience.

It was with some trepidation that I approached listening to this unit—while everything Eelco and I discussed was within my realm of knowledge on digital sampling and filtering, the effects aren’t particularly tested in hi-fi. Sure, I’ve heard poor resampling in professional film and music production projects I’ve worked on, but how meaningfully audible would it be in my stereo system?

Put a “Grimm Audio MU1” smile on my face

Well, color me impressed. The Grimm article on their Pure Nyquist technique comments that: “The sonic improvements are probably best characterized as “regained resolution.” The absence of digital harshness results in a fluid, analog-like sound where the sound stage opens up, gains in depth, and details become a natural part of the total scene. Standard formats can be appreciated in a whole new light, demonstrating a quality previously attributed to high resolution recordings, while high resolution file formats sound better than ever before. Performance finally seems to become in line with the quality indicated by the measurement figures and the mathematical laws of digital sampling as posed by Harry Nyquist in 1928. We therefore call it “Pure Nyquist.”

I can’t really argue with this description. Through the AES input it was indeed as if there was more detail, more transparency and a more coherent and dynamically liquid presentation. Imaging did not change in sharpness but did become denser and more tactile. Backgrounds seemed darker and images more separated and defined, without having their fundamental character changed. I wouldn’t go so far as to say it sounded like vinyl, or anything of that nature, but it was clear to me when compared to the USB output for example, that the efforts regarding jitter, power supply noise and that FPGA and Pure Nyquist filter technology were indeed making things happen.

“Whatever audiophile bingo term you prefer, the Grimm Audio MU1 does it.”

I’m afraid I can’t wax much more poetic than that. As the British describe their beer, so too the Grimm Audio MU1 does what it says on the tin. There’s a certain pro audio company rather playfully named Bettermaker, and the moniker sticks in my head for those choice pieces of gear which don’t seem to alter the source in any other way than to make it better. Clearer, more resolving, transparent, whatever audiophile bingo term you prefer, the Grimm Audio MU1 does it.

Now, I don’t want to overstate what the MU1 does. It’s a music server, and through the USB output for example, I noticed no difference between it and my Intel Nuc, which retails for significantly less. To get this magic, you must use the AES output, though Eelco did mention support for the S/PDIF output to follow.

I’m left then with a difficult proposition. The Grimm Audio MU1 is fantastically easy to use. You simply plug it in, it detects Roon, and you’re good to go. It’s actually one of the easiest music server setups I’ve ever seen. Sound-wise the result of Grimm’s obsessive FPGA is clear, there was no doubt that the AES output was superior to the USB. But one can have a serious pair of speakers and a competent amplifier for the price of just this one music server.

I am not yet the intended audience for this product. To me, while it was a wonderful sound, it still did not reach anywhere near the level of difference one might hear between speakers, amplifiers or some good room treatment. However what it does offer fires straight to the heart of what I value most in hi-fi—the elusive and technically mysterious sense of engagement we get from the best classic gear. One needs some experience as a system builder and listener to understand this concept I think, and I say that having learned it through much damage to my pocketbook, not out of any sense of audiophile pride.

The Grimm Audio MU1 to me, is a product that demands an experienced audiophile, and an experienced ear. It also demands a large pocketbook and a fanatical devotion to perfection at any cost. If you meet those criteria, and you’ve got an idea of why the technical sundae toppings of the MU1 make a difference, this unit might actually delight. It brings a level of digital refinement and ease to very good DACs that isn’t something you can really replicate with any other device that I know of on the market.

If you’re in the pursuit of the best, I can see this server taking an epic system to the very summit of the peak. For the true digital perfectionist, this could very well be the perfect piece of summit-fi you didn’t know you needed. For the rest of us, there’s many great flavors of beer.

Grimm Audio MU1 Pricing

  • MU1 (without storage) $10,700 USD (excluding VAT)
  • SSD 2TB add $375 USD
  • SSD 8TB add $1,020 USD