Bode plot of jitter and phase noise performance for the Micro Clock mk2, the Grimm CC-1, and the Audiophilleo AP1

Recently we sent our Micro Clock mk2 to the folks at Positive Feedback for a review. During the course of conversation, they revealed that their main clock was a Grimm CC-1. Grimm is a company whose name is synonymous with high end digital audio.  Their  designers have had profound influence on my approach to digital circuitry, and some of their philosophies served as a fundamental aspect of the Micro Clock mk2′s architecture. Imagine my surprise when Positive Feedback sent us Bode plots showing the jitter and phase noise performance of both the Micro Clock mk2 and the Grimm CC-1. Also included in the plot is a unit known as the Audiophilleo, which I am not familiar with.   I know the performance numbers of the Micro Clock mk2, but I was surprised to see that its jitter and phase noise measurements were a tiny bit better than the Grimm in these tests. These slight differences between the two aren’t audible, but it makes me proud to see how well our humble, silly little Micro Clock mk2 performs compared to a design that I would consider to be among the best.

Q: What is Jitter?

A: A very broad definition of jitter could be something like this:  Any variation of the frequency, amplitude, or phase of harmonics within a given clock or data signal.  There are actually two types of jitter: Random Jitter and Deterministic Jitter.  Without getting too complex, Random Jitter is jitter that appears randomly from the signal generation.  It’s caused only by errors within the crystal oscillator and not by any outside force.  Deterministic Jitter is the opposite in a sense.  It’s caused by an outside force acting upon the behavior of the crystal oscillator.

For the purpose of audio applications, jitter would be more narrowly defined as any unwanted and unrelated artifact that appears within the lower half of clock signal–a form of Deterministic Jitter.  Typically, measurement equipment will place the most emphasis on frequencies between 0Hz on up to approximately 1/2 the clock signal frequency.  So if we use a 44.1kHz signal as an example, we will mostly look for jitter between 0Hz and roughly 22kHz.  Imagine for a second that we look at our 44.1kHz signal on a piece of test equipment.  We’ll see the 44.1kHz fundamental as well as harmonics that extend upward in frequency.  But then imagine that we also see something else: a 13.26kHz signal roughly 80dB lower than our 44.1kHz fundamental.  This 13.26kHz signal would be an example of jitter.  It bears no true relationship to the 44.1kHz fundamental, and is there because of some interference from an outside source, like power supply noise, switching harmonics, etc.

Check us out next week for a new Q&A!