As you probably took note of, there is no USB output. The reason becomes crystal when you consider the design philosophy. Grimm put enormous effort into getting the very best clock signal. Why now discard it by using USB which contains no clock? For us it meant that we couldn't use our Mytek Brooklyn Bridge as DAC. Fortunately we had two alternates, a TotalDac Direct D1 and a T+A DSD DAC8. The first is a discrete R2R ladder with defeatable upsampler, the T+A DAC a chip-based design which automatically upsamples to 352.8kHz. These machines would offer nice hardware comparisons for later.

Each time we receive products from Grimm Audio to review, they are hand delivered—The Netherlands are small—to offer plenty of time to discuss various issues. In general the company does well and the list of dealers for the LS1 loudspeakers and now MU1 is growing especially in Asia. Then the conversation considered possible reasons why many 16/44.1 files streamed from Qobuz and Tidal can sound very different from store-bought CD. Sometimes streaming them from the cloud adds some sort of flutter. Eelco did bit tests of several Tidal and Qobuz tracks which usually were 100% perfect copies. However, he also found deviations. Sometimes there is a difference between the master stamped to CD and the 'remaster' offered to the streaming services. That simply shouldn't sound like flutter. The likely cause? Record companies add watermarks to keep track of illegal copies. It is not difficult to copy incoming streams—AudFree is an example—to burn them to CD and sell pirated discs (not condoned by us!).

With a watermark in place, it's possible to track back the copy to a streaming service. Now what? Removing the watermark is hardly possible without damaging content to add audible distortion. According to a Microsoft paper on digital watermarking, the watermark sits within the 1kHz-3.6kHz band. Often the resultant signal quality is similar to that of MP3. Such watermarking plus the fact that the versions offered to streaming services are sometimes 'remastered' to reduce dynamic range can be the cause for disappointing sound quality of virtual media. But there's an upside from an unlikely source. Some files at Tidal are called high resolution and labeled MQA. It seems that here record companies take virgin masters to put them through the MQA origami process. The result is that those MQA versions even in a non-unfolded state and converted by a non-MQA DAC to us sound better than their non-MQA versions. Here MQA is useful and Bob Stuart explains some of it here.

MQA origami unfolding with Grimm overlay on ideal jitter behavior on both sides of the AD/DA divide.

Returning the conversation to the MU1, Eelco called it an audio hub able to convert any incoming signal to 176.4/192kHz so that their LS1's processing offloads to sound its best. The same holds true for any other audio chain with a non-Grimm DAC and non-Grimm speakers. All D/D conversion duties like upsampling of incoming PCM or downsampling DXD and DSD 128/256 are performed by Grimm's custom-coded FPGA. You might wonder why one would downsample higher-resolution formats. The answer is simple. The maximum sample rate for S/PDIF is 192kHz. USB supports 384kHz but eliminates a clock signal. S/PDIF's embedded clock signal meeting the MU1's superior clock is sonically far more relevant than sample rates above 192kHz!