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GRIMM AUDIO MU2

GRIMM AUDIO MU2  REFERENCE DIGITAL MUSIC PLAYER

" The level of naturalness and resolution was staggering. With an estimated price of $17,500, this digital source is a real bomb, likely able to beat all of the most expensive sources of the moment "

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GRIMM Audio - MU2
The Ultimate Digital Music Player

“The MU2 is the ultimate digital music player: attractive, reliable and precise”

 

We are convinced that smart integration of functions yields higher audio quality. The MU2 combines a music streamer with a superb DAC and a reference quality analog pre amp. Its built-in DAC takes full advantage of the Grimm Audio low jitter clock and high performance FPGA processor. A relay based analog volume control enables the MU2 to become the true ‘hub’ of your hifi system for both digital and analog sources. Just like with its sister product, the ‘digital output’ MU1, a Roon Labs Core server is on board so no external computer is needed to enjoy perfect streaming. 

“The MU2 offers full integration of functions, from Roon to analog volume control, with revolutionary sound quality.”

 

At the heart of the MU2, Grimm Audio’s proprietary Major DAC can be found. It is of a groundbreaking discrete design that makes optimal use of our own FPGA board. In a unique way our high resolution Pure Nyquist upsampling filters are combined with a fundamentally flawless 11th order noise shaper of 1.5 bit. If you like to read more about this technology, we discuss the Major DAC in the next section further below.=

As a result the MU2 reproduces micro-details so well that it allows a deep emotional connection to the musical performance. The stereo image is of groundbreaking quality. Its serenity invites prolonged listening sessions.

 

If you love your loudspeakers and power amplifiers but long for a fundamental update in sound quality and streamer experience, the MU2 is designed for you.

 

The MU2 has 2 stereo analog inputs and 3 stereo digital inputs. It has outputs on XLR and RCA, and headphones jack.

About the Grimm Major DAC

In this section we present a more detailed background of the design principles of the Grimm Audio ‘Major DAC’ digital to analog converter in our MU2 music streamer :

 

Converting a digital signal into analog has always been a major challenge, which is clearly demonstrated by the abundance of DA conversion concepts that have seen the light over the years. In our experience high quality audio requires an extreme linearity and dynamic range. Even though modern chip technology allows for very advanced implementations, none of these seem to fully satisfy the high-end audio enthusiast. To circumvent these limitations a few companies acquired more design freedom by using a ‘discrete DAC’ approach in which all digital and analog stages of the DAC are developed in house. This clearly was the way to go for us as well. In a project of three years we created a unique digital to analog converter that has an optimal combination of dedicated DAC pre-processing in FPGA and our own discrete DAC hardware.

 

Existing techniques either use multi-bit conversion, a single-bit (bitstream) conversion, or a smart combination of these called Pulse Width Modulation (PWM) conversion. Conventional multi-bit conversion uses a voltage level per bit, which demands an extreme precision of the linearity of the larger bit steps. For example, the largest bit step is many thousands times larger than the smallest bit step, but should have the same precision as that smallest step, otherwise adding that small step makes no sense. To reach more than 18 bits precision with this technique is extremely difficult. As a result these types of DACs show distortion of micro-dynamics in the music. Also, cross-talk from the conversion control signals can cause graininess or harshness in their sound character.

 

To get around these problems, Philips introduced the ‘bitstream’ single bit technology end of the 80’s. Later it was adopted for SACD as ‘DSD’ format. In theory, a single bit type of DAC is inherently linear, as the single bit voltage level is always ‘precise’. But a single bit converter of course can only represent two signal levels instead of the thousands of a multi-bit, which means it has a much higher noise level. To make this technique work for audio, the actual conversion is created by very fast switching of the single bit value through oversampling, and then pushing the high noise away from the audio band into the inaudible region above 20 kHz by means of a noise shaper. 

 

This process brings other challenges to a DA converter unfortunately. For instance, there are more stringent requirements on the jitter performance of the clock. Also, this technique unavoidably puts a significant amount of high frequency energy on the DAC output, which can be tough for the following amplification stages. Moreover, in a single bit architecture, the high frequency components modulate in a way that’s depending on the audio signal. Because of this signal dependent efficiency, digital noise shaper systems operate with limited ‘stability’. As a result, the transparency and audible coherence are compromised.

 

In a PWM DAC, the disadvantages of the single bit architecture have been overcome by using a couple of bits (e.g. 5) and then representing their values by a varying width of the single bit stream (PWM stands for “Pulse Width Modulation”). Since there are still just two voltage levels, the system remains inherently linear. Again, a noise shaper is required to create the DAC signal. However – unlike with single bit architecture – the noise shaper now operates with a constant efficiency. On the downside an even higher clock frequency than with the single bit solution is required. And, more importantly, the implementation of such a noise shaper demands extreme processing power. In any practical realization, this results in a compromised implementation, which inevitably translates to a compromised sound quality. 

 

The MU2 ‘Major DAC’ has been placed on the optimal middle ground between all these options. It is using a 1.5 bit architecture. Amplitude linearity is inherently guaranteed as the 1.5 bit value is represented with a single bit D/A cell, in ‘PWM style’. Like with PWM DACs, the noise shaper is running with an effectively constant efficiency, realizing a linear operation over the entire dynamic range, as illustrated in the graphs below. 

 

This still requires extensive processing power, which – thanks to the lean 1.5 bit architecture – can be exploited completely to realize a flawless system in a powerful FPGA. The implemented solution in the Major DAC results in a zero error operation of the noise shaper. Moreover, the 1.5 bit DAC choice offers such a stable noise shaping operation that it allows for a highly optimized, unique 11th (!) order noise shaper. 

To filter the resulting strong high frequency noise before it enters the analog signal path a so-called FIR DAC topology is employed, using 16 DAC cells per channel. And while we are on the topic of filtering: worth noting is that the input of the noise shaper is fed from our extreme precision “Pure Nyquist” digital FPGA filter, running at 128 times the base rate. All these measures enable the Major DAC to reproduce micro-details in the audio that have never been heard before. 

 

Special care is taken in the analog signal path to preserve the beauty and transparency of the DAC output signals. The analog signal path is implemented fully symmetrically using very high quality circuitry, components and layout. The signal is routed through a first-class, relay based volume control section so that the analog output of the MU2 can be fed directly into a power amplifier. Additionally, up to two analog sources can be connected, allowing the MU2 to be both the digital and analog ‘hub’ in your HIFI system.

 

 

Grimm Audio MU2 features

  • Roon Core and Roon End Point integrated

  • Ultra low clock jitter

  • FPGA based discrete Major DAC

  • All sample rates and formats supported 

  • Relay based analog volume control - from +8 dB to -79 dB in 1 dB steps

  • AES, spdif and optical digital stereo inputs 

  • Analog XLR and RCA inputs

  • Analog XLR and RCA outputs

  • Headphone output - max 40 mW into 30 Ohm, 55 mW into 600 Ohm=

  • Can be used with CD-Transport [descriptive download below]

  • Web control of setup via any browser

  • Infrared remote control

  • External USB and NAS storage, optional internal SSD

  • Tidal and Qobuz support

  • 355 x 85 x 295mm (WxHxD)

  • 5 year limited warranty

Clock specifications

 

  • Internal intrinsic clock jitter < 0.6 ps RMS (> 10 Hz).

  • Can slave to 44.1 kHz and 48 kHz based digital sources at 1FS, 2FS and 4FS +/- 50ppm

  • The output will mute for 80 ms when changing clock base rates.

Sample rate conversion with fpga processor

 

  • Upsampling of 1FS and 2FS files, streams and digital sources to 4FS or 2FS with “Pure Nyquist” decimation filter

  • Downsampling of DSD64, DSD128, DSD256 and DXD files and streams to 4FS or 2FS with “Pure Nyquist” decimation filter

  • Optional FPGA volume control on Digital 1 and 2 outputs, and S/PDIF in case no LS1 is connected : from 0 dB to -63 dB in 0.5 dB (partly 1 dB) steps.

  • Latency from digital in to digital out: 11 ms at 48 kHz.

 

Major DAC features

  • 11th order flawless Noise Shaping

  • 1.5bit architecture, 1bit cell, at 512fs rate

  • 128fs Pure Nyquist oversampling principles used throughout

  • Smart, extended settling technology

  • Intersample overs supported without clipping

  • 16-tap FIR-DAC topology

  • Fully symmetric analog signal path

  • Ultra stable local power supply technology

  

 

Grimm Audio MU2

$ 17,500

Optional SSD Storage - 1TB

$ 240

Optional SSD Storage - 8TB

$ 630

No Sales Tax outside of State of TN

 

 

MU2 with SSD Atelier 13 Audio Stock Arrivals :

4 x MU2  at end of May,  2024 

If you pre-order, we can specify 2TB or 8TB SSD before arrival.

Digital Adapter Cables

Coax AES3 XLR female to Spdif RCA / 1 meter

$ 185

 

Coax Spdif RCA to AES3 XLR male / 3 meters

$ 235

 

Coax AES3 to Spdif & Spdif to AES3 adapter cable set 1 meter

$ 370

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HARDWARE
MANUAL

CD TRANSPORT
GUIDE

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ASSOCIATED
REVIEWS

GRIMM AUDIO
MU1

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... what they say ...

 

Twittering Machines

Micael Lavorgna | March 21, 2024

If you want to hear the best digital music reproduction I’ve heard by an obvious and distinct margin, you’ll need to find a Grimm MU2 to listen through.

 

That’s it, that’s my conclusion ... the Grimm MU2 acting as Roon server, Roon endpoint, and DAC made music sound at once less processed and more fully fleshed out than other digital solution(s) I’ve had the pleasure of hearing. What’s more, the MU2’s analog volume control and line level inputs turned it into a wonderful sounding preamplifier to boot. All in one.

 

The Grimm MU2 can act as a Roon Core (server), Roon Endpoint (streamer), DAC (digital to analog converter), and analog preamp all in one, which is the way I used it for most of the serious listening part of this review. The internal SSD storage is optional and comes in two sizes: 2TB or 8TB and adds $235 or $630 to the MU2’s price respectively. Money well spent as far as I’m concerned. Now I know some people wonder if (or pretend to know that) having a server, streamer, and DAC all in one box may compromise sound quality and I can tell you that is just not the case with the Grimm MU2. No way, no how. How do I know? Because of how it makes music sent through it sound.

 

One the biggest of the MU2’s many surprises was just how expert it was at getting out of music’s way while leaving behind the most finely refined and revealing re-production in its wake. The music contained on Natural Wonder Beauty Concept stutters, stops and starts as if made by some elaborate soulful automaton with electronic sounds emerging from silence in reach out and touch it dimensional form feeling as real as bubbles floating in air. The review system comprised of the Vivid GIYA G3 Series 2 speakers driven by the Audionet HUMBOLDT integrated amp was, along with other things, a master of purity in sound, extra especially so when paired with the MU2 making this rich dense dance of a record come to stunning life in Barn.

 

I know what some of you are thinking—Did you try the MU2’s digital inputs with an outboard streamer to see if that’s even better? Or—Is the Grimm MU1 paired with some other DAC and a real high-end server even better than the MU2 package?

 

And my answer is you haven’t heard what I’ve been saying … so I will repeat what I said at the outset of my review ... If you want to hear the best digital music reproduction I’ve heard by an obvious and distinct margin, you’ll need to find a Grimm MU2 to listen through.

Read the full Review here ...

 

 

 

MU2 User Review

Sharing my first impressions with the MU2

"A new window of truth"

After receiving a new unit, with SSD this time, it took about 2 hours to tranfer all the music files. That was easy, although the albums in the library from Qobuz somehow only loaded the album covers after 1.5 days or so. Powered it up playing Red Hot Chili Peppers on repeat for the same 1.5 days. Then, I just made sure Flea's bass guitar boiled the last nano-drops of water out of the silicon before doing any serious auditioning.

 

I took quite a gamble when ordering the MU2 without trying it out first. ! assumed it would blend into my carefully matched set-up, and hoped trhat it would not shift the balance. My previous experience with the MU1, and Grimm's excellent reputation, made that a calculated guess. But still a guess.

 

But oh boy ! ...  it just took 2 seconds to put an end to any post-decisional regrets. Take the MU1's ability to paint an image that is spacious, natural and completely credible. Multiply that times 2, and that is what the MU2 does. My previous DAC  (Sonnet Pasithea)  had a very good way of projecting a 3D soundstage where everything has its place and was easy to follow. One of the reasons why I preferred it over the Dave DAC which I sometimes found a bit too upfront, or the Tambaqui which also offered an excellent soundstage but at twice the price and sometimes at the expense of the bloom and naturalness ... Disclaimer : to my ears, my setup, my listening room and my budget, not as an absolute statement... The MU2 expands that soundstage even further back, but also much much wider and far beyond the boundaries of my speakers or listening room.

 

But I'm most impressed by the total naturalness of that space and the coherent way everything has its position in that space. How the tiny sounds hold their touch to their origin, for example the reverb connected to the singer and the recording space. It is just incredible. A new window of truth.

I know that I need to do more hours of burn in and listening to get beyond these first impressions. I suspect that the bloom and (micro-)dynamics might improve further, as they still seem a little bit reserved at times. Also, I'd like to share a comparison of the built-in attenuator with the one in my integrated SPEC amp. With the Pasithea I eventually prefered the analog SPEC attenuator over the digital one of the Pasithea. I think it is a good thing Grimm decided to use an analog attenuator as well, but making a "dB-matched" comparison needs more time and commitment.

It is very nice to adjust the volume via the Roon interface, and hearing the gentle clicks of the relays under the (Silver!) central disc. 

 

Am I enthusiastic ? Yes I am. Ecstatic is an even more exact description of how I feel. So, is this the giant DAC killer? I don't know. I didn't try the dCS's, Goldmund's, Gryphon's, Nagra's and the likes here at my home. I don't have the budget to justify the audition, so I can't make any fair statements.

 

What I do know are the experiences I had listening to 6/7-figure set-ups that impressed me the most at audio shows or at hifi dealers ... that feeling of a total lack of distortion freeing the brain so music seems slightly slower and easier to follow ...

 

... and this is the very same feeling I have now listening to the Grimm MU2 on my own sofa in my listening room.

 

 

 

MU2 Initial Reactions

Munich High End Show June 2023

MU2 amazes High End Munich Audience

The presentation of our new MU2 mus
ic streamer with built-in DAC at the High End Munich show was a great succes. Many visitors congratulated us with the massive stereo image, controlled low end, and overall ease of listening. Often we were given a thumbs up and big smile when people left the room.

 

Jaap Veenstra and Martijn ten Napel of Dutch online magazine Alpha Audio made video reviews of the show (in English) and visited our room twice. It’s clear that they were blown away. You can find their response to the MU2 sound in their first day report (at 7’24”) and especially in their third day report (at 16’15”), after they returned. Jaap also did a video interview about the MU2 with Eelco Grimm. 

MU1 Reviews

MU1 = MU2 without the Grimm Major DAC

 

 

The device activates the hug hormone

Ruud Jonker, Hifi.nl, Amsterdam

 

The MU1 takes my breath away

Leung Wing Lun, SuperAV, Shanghai

 

Today we listened to nothing less than a true revolution in High End Audio listening
Erwin Pakasi, Barendrecht

 

The Grimm MU1 manages to touch the essence of the music
Jaap Veenstra, Alpha Audio, Haarlem

The MU1 transforms CDs into terrific source material!
Bart, Kortrijk

I give the the MU1 6 of 5 possible stars in sound quality.

An amazing device!
Wieland Hornig, Berlin

Test Grimm Audio MU1 - best sounding network player on the market?
Jurgen Schroeder | Low Beats | August 18, 2022

 

 

Music player with the best sound on the market – Grimm Audio describes the MU1 with this crisp statement in the intro of its operating instructions. It literally says: "It is designed to be the most sophisticated and best sounding music player on the market." Ambitious claim - ambitious price :

 

At exactly 11,211 euros, the Grimm Audio MU1 is really no bargain. However, the products of the Dutch audio specialist Grimm Audio enjoy an excellent reputation worldwide for their outstanding sound quality. This is also the case with LowBeats , where the LS1be active loudspeaker set plus SB1 subwoofer earned the award “Unmatched objective – recommended for professional audio and hi-fi alike”.

 

So it's not for nothing that Opera star Jonas Kaufmann now belongs to the convinced Grimm LS1be listeners !

 

Grimm audio products are always characterized by their innovative and radical concept. Functionality and the very best sound quality are given absolute priority - the Dutch, on the other hand, consistently dispense with audiophile chichi. This also applies without restriction to the Grimm Audio MU1: The elegant, minimalist aluminum housing with the top-positioned, cleverly embedded rotary encoder also makes the elegant digital player the visual center of the hi-fi system.


Functionally, this is the case anyway, as the MU1 combines Roon music server, network player/streamer plus digital processor pre-stage in one housing - optionally even with an integrated SSD music data archive with up to a whopping 8 terabytes of storage capacity. Yet another highlight: since the last firmware update (v1.4 at the time of testing), the Grimm Audio MU1 can not only play-back in stereo, but also multi-channel in 5.0 format.

 

 

Grimm Audio MU1: concept and connectivity

As a purely digital player without its own D/A converter, the MU1 is initially intended - but by no means exclusively - as a music supplier for the Grimm LS1 active loudspeaker systems. For these, it has dedicated connection options in the form of a special RJ45 Ethernet socket. Active loudspeakers or DACs from other manufacturers, on the other hand, can dock via two AES3 or a coaxial S/PDIF output.

 

All three digital outputs have their own volume controls that can be switched off. Clever solution: Although these obey the volume slider in the Roon app, Grimm Audio uses a self-developed, high-quality circuit for the actual slider for the best sound quality. Conversely, the Roon fader moves optically synchronously if you use the above, smoothly running rotary selector to adjust the volume.

 

The Grimm MU1 has three inputs for connecting digital signal sources: AES3 XLR symmetrical and S/PDIF coaxial or optical. The special thing about this: In order to free them from jitter-related artefacts, the audio signals of all three inputs run through the on-board, digital clock processing (reclocking). In addition, the MU1 has two USB-A sockets for connecting external storage media such as USB sticks or hard drives - except for APFS (Apple File System), almost all formatting standards are allowed here. Since external data carriers are read by the computer and are therefore "passive", reclocking can be omitted for USB playback.


In addition to the inputs and outputs for digital audio, the MU1 has other connections. First of all, there is the RJ45 Ethernet socket, which is usual for network players. This is “mandatory”, since the chic Dutchman has nothing to do with WLAN. The reason for this is the unreliable data transmission in connection with Hi-Res players such as the integrated Roon. Also worth mentioning is the 3.5 millimeter stereo jack for connecting an IR sensor: This makes it possible to control the Grimm Audio MU1 with programmable infrared remote controls. A rather unusual feature, on the other hand, is the coaxial 75-ohm socket for connecting an antenna for the optionally retrofittable VHF receiver module.

 

 

The Technology

As usual with digital music players, the Grimm MU1 is also quite clear when looking inside. On closer inspection, however, one recognizes the strategically consistent focus on the best sound properties. Roon was chosen as the music server not only because of its straightforward signal flow, the comfort it offers and the many technical possibilities. Roon is also programmed extremely efficiently and therefore requires little computing power. This in turn allows the use of energy-saving, fanless digital technology - implemented in the MU1 using an Intel NUC board with a Core i3 processor. Even with future Roon extensions, it runs more or less at "idle gas" and thus loads the interior of the device with negligible high-frequency interference energy.


The topic of power supply is usually rather underestimated, but also relevant to the sound of digital equipment. That's why Grimm Audio relies on an in-house power supply for the MU1, developed by a proven specialist in switched-mode power supply technology. Properly conceived and made, the latter can actually be superior to the classic, linear power supplies - especially when it comes to freedom from the 50 Hertz interference components that are always present in linear power supplies, including their multiples.

However, Grimm Audio is particularly proud of the signal processor board in the MU1, which was also developed in-house. This accommodates several function blocks and thus forms the constructive and tonal "centre" in the device. Those who are curious will therefore find this unit described in more detail in the following chapter.

In fact, the term "digital audio technology" suggests that the musical information content is completely contained in the stored, more or less precise samples. However, this is only half the truth: Tones, sounds or noises are naturally always characterized by a certain duration. Samples, i.e. instantaneous values, alone do not provide any information on the frequency spectrum and pitch of a music track due to the principle - these only result from the defined clocked reading of consecutive samples.

It is clear that this process should take place in the same time pattern as the step-by-step acquisition of the sample values, i.e. the A/D conversion. If, on the other hand, you play a 96 kHz recording at a clock rate of 48 kHz, the music sounds an octave lower – with twice the playing time. This connection already gives an idea: Even the finest, ultra-short deviations in the clock signal (jitter) always leave their "scratches" in the music: It sounds rougher, less sharp - although absolutely nothing has changed in terms of the sampling values ​​themselves or their number.

Jitter is therefore a central, sound-defining topic in digital audio. Therefore, the data center responsible for the audio data output in the Grimm Audio MU1 has two clock generator units optimized for audio applications. The first from the Dutch specialist Tentlabs is used to clock the computer, which will be discussed later. For the actual audio clock, on the other hand, an extremely precise, discretely constructed unit is used. These are similar to those that Grimm Audio also uses in their recording studio master clocks CC1 and CC2 . The design focus is clearly on the sound-defining properties, i.e.: ultra-precise clock sequence with low phase noise.

Jitter – thought through


However, the described, classic solution to the jitter problem was not far-reaching enough for the Grimm developers. Rather, they pursued the question: "What actually happens when the individual sampled values ​​also show irregularly distributed inaccuracies in terms of level?" As the previous chapter already suggests, this effect - I'll call it "amplitude jitter" - has an effect on the sound as well as temporal jitter; in other words: through roughness and blurriness. In principle, the condition does not matter whether it is “right amplitude at the wrong time” or “wrong amplitude at the right time”: the perceived envelope of the signal is equally deformed. Time or amplitude errors in A/D and D/A conversion deform the envelope in the same way.


Time or amplitude errors during A/D (blue curves) and D/A conversion (red curves) also deform the signal envelope (Graphic: Grimm Audio)
"Amplitude jitter" is mainly caused by spurious spectra and mathematical inaccuracies, mainly caused by bitstream converters and digital filters integrated into conventional DAC chips. These are used to speed up the incoming multi-bit PCM signals for the actual D/A converter stage, which only works with a small word length (upsampling). In order to improve the internal signal-to-noise ratio, this is done in several consecutive stages. The very first one is particularly critical: Although it only accelerates slightly (about a factor of 4), it requires the most computing power because it is fed with the entire PCM word width.

Mathematical artist FPGA


In fact, this stage requires significantly more computing power than conventional D/A converters can accommodate on the chip for reasons of space and cost. This is exactly where the Grimm Audio MU1 comes into play again. In order to free the downstream DAC from its error-prone calculation work, it quickly relocates the sound-sensitive process of the first upsampler stage to its own work environment. The DAC thus receives an already processed signal, which allows it to work much more precisely.

 

The Grimm Audio MU1, on the other hand, manages such demanding calculations with an in-house developed board that is exclusively responsible for digital signal processing. Equipped with a high-performance "Field Programmable Gate Array" (FPGA), not only does upsampling and downsampling take place here, along with the associated filter work - reclocking also takes place here, which is intended to free incoming signals from jitter via the digital inputs. Not to forget the switchable, precise volume controls for the three digital outputs.


Roon power users might object at this point, "Why so complicated? Roon already has a lavishly equipped software sampling rate converter on board.” That's true, but the makers of Grimm Audio don't calculate it precisely enough. Rather, they added two more software specialists to the development team who were specifically responsible for programming the FPGA. What exactly happens there and with what word length it calculates remains a Grimm secret. In any case, the term "Pure Nyquist Filter" implies that it is a wideband filter with a perfectly linear frequency response and infinite edge steepness above half the sampling rate - the Nyquist frequency.

 

In view of such intensive efforts for a perfectly processed digital signal, it is understandable that the Grimm Audio MU1 does not have a USB output with the typical off-the-shelf chipset. Digital Out is therefore only available via AES3 or S/PDIF – in other words: 24-bit PCM up to a maximum of 192 kilohertz. A corresponding downsampling is therefore carried out for 1-bit soundtracks up to DSD256.

 

 

The MU1 in use


Anyone who has ever heard music via Roon will be able to use the Grimm Audio MU1 immediately. The initial setup is not rocket science either: it is important to install the corresponding Grimm extension for volume control synchronization in your personal Roon account. Since firmware update 1.4, there are two alternatives for the device setup itself. On the one hand directly on the MU1 via the front display by selecting a menu and confirming with a rotary encoder, on the other hand via smartphone, tablet or computer and any browser. A clever idea here: if desired, the MU1 display shows a QR code with which its web address in the network can be called up directly using a tablet camera - and you're right in the middle of the menu.


Wiring multi-channel systems requires a little more attention. There are certain differences in the signal flow here when it comes to mixed systems made up of Grimm LS1 systems and other active loudspeakers or DACs. But even newcomers shouldn't feel overwhelmed, as the operating manual lists practical wiring examples for all possible multi-channel configurations. In any case, the MU1 operating instructions are easy to understand and quite informative - especially when it comes to the topic "calibrated monitoring volume with MU1 and LS1". This is where the expertise of Grimm Audio boss Eelco Grimm comes into play: not least because of his work in the renowned Audio Engineering Society (AES)thanks to the fact that the "Loudness War", which has now lasted for more than two decades, is gradually coming to an end.

 

 

Listening


The technical preparations for the listening test with the Grimm MU1 took a little longer this time. The reason: Two independent Roon servers in the same network do not get along. The Grimm Audio MU1 and our editorial "rooner", a QNAP HS-453DX, would therefore be on a collision course. With a few tricks, however, the threat of a skirmish over competence could be avoided. This cleared the way for an AB comparison between the Grimm Audio MU1 and our Roon-compatible digital player, the Lumin U1 - albeit with a drop of bitterness : Because it allows the highest transfer rates, we usually feed external D/A converters from the USB output of the Lumin U1. As already mentioned, the Grimm Audio MU1 deliberately does without this, which is why we used the AES3 outputs for the listening comparison under identical conditions.

 

The Merason DAC-1 served as the reference D/A converter in the listening test setup , which passed its analog output signal to the Neukomm CPA155S integrated amplifier, which had also been tested. Finally, the Fink Team Borg acted as sound transducers in the illustrious playback chain.

In the listening test report for the Grimm MU1 Merason combination, these two words were often found: "Clearly better." This applied both to the distance to the competing team and to the way in which it was revealed in terms of sound. In fact, the comparison between a sparkling clean, absolutely transparent glass pane and a minimally covered glass pane, which tends to scatter light, is close. The music played from the MU1 sounded more concrete, direct, tangible, more colorful, sharper contours and more plastic than with the Lumin U1. After all, it was able to gain a little more in terms of transparency and immediacy via its USB output. With its exemplary permeability, however, the Grimm MU1 played even more captivatingly, more engaged. So it was not for nothing that we chose the HiFi setup described above for the Test of the Siltech speaker cable trio .

 

The Grimm Audio MU1 gave a particularly impressive performance on the excellent HEDD Type 07 Mk2 active monitors , controlled via AES3 110 ohm digital cable (Mogami Neglex #3080). Like most pro audio monitors, the HEDDs operate at an internal sampling rate of 96 kHz. Exactly for this purpose the resampler in the MU1 offers a mode that, depending on the program material, either carries out double upsampling (e.g. from 48kHz to 96kHz) or carries out two or four times downsampling (e.g. from 192kHz, 384kHz and DSD to 96kHz).

 

In terms of sound, I really appreciate the HEDD Type 07 Mk2 with its digital phase compensation. However, I have never experienced them so convincingly as in combination with the Grimm Audio MU1. What was still dormant in the recordings in terms of spatial depth and tonal plasticity - for example in the beautiful title Mare Nostrum by Trio Paolo Fresu | Richard Galliano | Jan Lundgren - was really stunning.

 

 

Grimm Audio MU1 – Conclusion


Viewed soberly, the Grimm Audio MU1 combines a high-quality network player with a comparatively complex signal processor. The first task of this is to feed the digital audio signal to the external D/A converter with as much clock precision as possible. In addition, it takes over the particularly computationally intensive, first stage of the always required sample rate conversion - a process that normally takes place entirely in the DAC chip itself. This shift allows the sound-critical resampling and filtering tasks to be performed much more precisely than conventional DAC chips with their limited processing capacity.

 

Of course, the external D/A converter still has the very last word in terms of sound. However, which part of this is credited to the preceding signal processing in MU1 depends on the properties of the respective hardware. In both cases, however, our listening test with two different system setups resulted in partly significantly better sound results with the Grimm Audio MU1 as the digital "foreman".

 

In terms of sound, this has a rather subtle effect, but musically it is all the more lasting. Appropriate terms for this are clarity, richness of detail and transparency; in other words : the veil is lifted more. All types of music benefit from this – even music that only partially corresponds to typical hi-fi listening habits.

Many young musicians these days deliberately use artificial distortion effects or granular synthesis as a stylistic device. Such fine textures, reproduced by average hi-fi systems - or even more blatant : Bluetooth speakers - either disappear completely or sound more like a defect than music.

 

As an exemplary permeable audio component, on the other hand, the Grimm Audio MU1 opens up completely new musical worlds for the listener.

Once experienced, there is hardly a way around it !!

ASSOCIATED
COMPONENT

GRIMM AUDIO
MU1 Digital Music Source

Server/Streamer
$12,500

 

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ASSOCIATED
COMPONENT

GRIMM AUDIO
SQM Cables

 

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ASSOCIATED
COMPONENT

WHEST BII
Mastering Buffer

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ASSOCIATED
COMPONENT

LessLoss C-MARC
Power Cord

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ASSOCIATED
COMPONENT

LessLoss Firewall 
640 X Power Filter

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ASSOCIATED
COMPONENT

AB-TECH REN
ETHERNET ISOLATOR CABLE

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ASSOCIATED
COMPONENT

AB-TECH KLAR
USB CABLE

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