JITTERSIMULATOR
There is an on-going debate about how much jitter is audible. To make the
situation even more complicated, jitter comes in several forms: random, deterministic,
data-correlated, etc. Jitter is also caused by different offset frequencies. Another reason for variety of experiences
and opinions is that effect of each form of jitter varies according to the
design of the DAC, among other things.
If you want to explore how the most common form of jitter affects your system, the Audiophilleo1 has an additional,
intentionally “noisy” clock that bypasses the internal reclocking circuitry. One can toggle between the normal and JitterSim modes via
a programmable remote control or using the Audiophilleo1 display:
- Level 0, Normal, JitterSim off. 2.6 ps RMS phase jitter, integrated from 10 Hz to 100 kHz. < 5 ps RMS period jitter. This is the default setting, without any artifically-added jitter.
-
Level 1, JitterSim On. Nominal 250 ps RMS period jitter and around 1300 ps RMS phase jitter,
integrated from 1 Hz to 100 kHz. These values are better than most integrated
computer audio outputs or the Bel Canto USB Link, for example, but not as good
as those of the best USB-S/PDIF interfaces.
The diagram below shows the effects on phase noise with the JitterSimulator turned on. The blue trace shows the normal phase noise response of the Audiophilleo1 using the 44.1 kHz sample rate clock, which is 2.8224 MHz. The RMS phase jitter from 1 Hz to 100 kHz is 8.2 ps. The magenta trace
shows the effects of added jitter, with the Audiophilleo1's JitterSimulator feature turned on. The RMS phase jitter is now 1300 ps (13 ns) from 1 Hz to 100 kHz.
which should be audible in many systems.
The phase noise spectrum, that is, jitter evaluated in the frequency domain, across a given bandwidth, is an important indicator of "real world" audio quality. This graph shows the clock phase noise when JitterSimulator Level 1 is enabled. Note that if the graph continued to higher frequencies, it would show a rising dBc trend because the reclock circuitry is bypassed. This intentionally generated jitter is generally uncorrelated to the audio data. Uncorrelated, or random jitter is usually less audible than correlated.
Because JitterSimulator generates only the less-audible uncorrelated form, another device with the same amount of correlated jitter could sound worse. JitterSimulator does not emulate all types of jitter, but at the very least will help educate your ears to the some of the common effects.