The topic of master clock has been on my mind for some time now. It's fascinating to see what sonic improvements can still be teased with it out of a digital chain. The brand new REF10 NANO from MUTEC is a variant of the outstanding REF10 that concentrates on the essentials at half the price.

That's quite an announcement and makes the subject of clocking even more interesting as it already is. I've had two cascaded MUTEC MC3+ USB re-clockers in my inventory for many years and am always amazed at how good a digital chain can sound with them. And since my two tests of the REF10 and REF10 SE120 master clocks, I also know that it can be much better. However, I've always had a certain stomach rumble when a clock that's at least four times as expensive "only" clocks the MC3+ USB. To help you better understand what I mean, I need to expand a little. A master clock, such as the REF10 NANO, generates an extremely low phase noise 10 MHz clock signal. But we can't do anything with that at first. Modern DACs work with clock frequencies of 22.5792MHz or 24.5760 MHz, which are integer multiples of the standard audio sampling rates 44.1, 88.2, 176.4kHz and 48.0, 96.0, 192.0 kHz. With USB2.0 we have a clock frequency of 48 MHz and typical Ethernet clock frequencies are 25 MHz, 125 MHz and 156.25 MHz. Nowhere do we find 10 MHz.

Thus, we need a converter that synthesizes the required audio clock frequencies from the 10 MHz clock. The magic formula is called a "digital frequency synthesis". The task of such a process is to generate any clock frequency on the basis of a reference clock of 10 MHz. It is obvious that the clock provided on this basis depends not only on the precision of the clock itself, but also on the quality of this synthesis. A prerequisite for the use of a master clock is therefore that the device to be clocked has such a frequency synthesizer and a connection for an external 10 MHz clock. Unfortunately, there are currently not too many manufacturers and devices in the high-end sector that take this, admittedly complex, approach. MUTEC has compiled a list of currently available 10 MHz-compatible audio devices on its website. But there are still more hurdles to overcome: there is no consensus among manufacturers as to whether the reference clock is provided in the form of a sine wave signal or a square wave signal. Accordingly, it cannot be ruled out that the built-in frequency synthesizer will cope better or worse with one or other signal form. To make matters worse, there are also two standards for interface and cable termination: 50 ohms on the one side and 75 ohms on the other. In the high-end sector, we encounter both standards.