GRIMM AUDIO MU1

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

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

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

An amazing device!
Wieland Hornig, Berlin

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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

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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

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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.

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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.

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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.

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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.

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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.

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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 !!