There are some devices that are difficult to place. The Grimm Audio MU1 is definitely such a device. Because, is it a streamer? No. Is it a server? No. Is it a central hub…? In a way. But it’s also more than just a hub. It’s a streamer, Roon server, upsampler and a digital hub… In short: a versatile device! And a fascinating platform to continue building upon.
Last year we saw a prototype of the Grimm Audio MU1 and later heard it in real life. The first impression was already very good. Not only does the device look beautiful: it sounded – sounds – very nice: big, precise, fluid. Of course all demos were on Grimm LS1 speakers. In short: we were not able to give a real verdict at the time. But now we do, because we have been able to test the MU1 in our own set. More about the performance later… first an overview of what this ‘hub’ can do!
Grimm of course has a name to uphold when it comes to clocking a digital signal. the CC1 is an example. The CC2 is the somewhat stripped down version. But these clocks are used in many studios for a reason. They’re extremely stable and precise.
The MU1 has a new kind of clock that has been given a FLL function. FLL stands for Frequency Locked Loop. The clock can lock on the incoming frequency if you select an spdif input for example. The method resembles PLL, but according to Grimm it is even less jittery. Of course, the resampler then also processes the signal again to further improve the result. Grimm reports that the MU1 can even lift a TV output or a cheap CD player to a very high level in this way.
We’ve already talked about the resampler / up- / oversampler. Now Eelco Grimm has explained the operation quite extensively in our interview in Eindhoven. You can see this video here. In short, all digital music streams go through the upsampler. This special upsampler makes it 24 bit / 192 kHz, or 176.4 kHz. Then this signal – super-tightly clocked – is sent out towards the d/a converter.
The advantage of this way of processing and transmitting is that the d/a-converter has less work to do. Because despite what some people think, most dacs don’t work with 16 or 24 bits. Almost every converter has its own internal format with which it works. This can be 1 bit with an ultra high frequency, but also 4, 5 or maybe 6 bits with a high sampling rate. In other words, the dac needs to process an incoming stream of data to make it suitable for d/a conversion. By already offering a high sampling rate, the dac does not have to calculate as hard and eventually the result is fewer rounding errors.
The condition is, however, that the preliminary work is done extremely precisely. And Grimm took care of that. The FPGA containing the upsampling software is an extremely powerful model, reports Grimm Audio.
In and outputs
Of course the Grimm Audio MU1 has a number of outputs. We see two AES outputs and a special LS1 output. The latter, of course, is for the LS1 series from Grimm. The fact that there are two AES outputs has to do with an update for surround in the future. Then there are a number of entrances: AES, Spdif, optical, two times usb (storage) and a tuner input. Right. Radio. The beauty with all these inputs, is that they can enjoy the extremely precise clock and the upsampler n the Grimm Audio MU1. whether it works, read on.