Jitter 102B


Member Sponsor & WBF Technical Expert
Jun 23, 2010
Monument, CO
<continued from Jitter 102A>

Now look what happens when the signal level is cut in half (-6 dBFS)


Ah, the noise floor drops, too, and ENOB stays about the same. With less signal, ENOB will go down since we are using less of the DAC’s range (reducing the number of bits used). Jitter drops because, as stated in Jitter 101, it is related to the slew rate of the signal. Smaller signal, lower slew rate, at least for a sinusoid. This is not true for something like a square wave that has faster edges (and thus higher frequency components – see the “Building a Square Wave” thread). So, jitter will degrade fast pulses more than a single tone like this test case.

Looking at a 10 kHz tone, 1 lsb of jitter is 1/10th that of the 1 kHz case (0.5 ns vs. 5 ns). As we’d expect, the results are about the same as the 1 kHz test case.


Now, increase the jitter to ~5 ns, equal to 1 lsb at 1 kHz, and performance is markedly lower:


Wow, 70 dB SINAD (signal to noise and distortion), and only a little over 11 bits! Ouch! SFDR is still high, over 100 dB, but the noise level is rising to audibility.

Now let’s return to a 1 kHz input with 5 ns (1 lsb at 1 kHz) jitter, but add 1 lsb of the input to the jitter. That is, nothing fancy, just a simple addition of 1 lsb (in time) modulation of the (formerly) random jitter on the clock. This is the dreaded deterministic jitter term.


Well, ENOB is about as before, but now there’s a 2 kHz tone sticking well above the noise floor. That is second-order distortion, i.e. a second harmonic that wsan’t there before. Probably not really audible at almost 100 dB down, but a very annoying thing to see. Dropping the signal amplitude reduces the distortion spur as well, just as before.


On to Jitter 102C...
Last edited:

About us

  • What’s Best Forum is THE forum for high end audio, product reviews, advice and sharing experiences on the best of everything else. This is THE place where audiophiles and audio companies discuss vintage, contemporary and new audio products, music servers, music streamers, computer audio, digital-to-analog converters, turntables, phono stages, cartridges, reel-to-reel tape machines, speakers, headphones and tube and solid-state amplification. Founded in 2010 What’s Best Forum invites intelligent and courteous people of all interests and backgrounds to describe and discuss the best of everything. From beginners to life-long hobbyists to industry professionals, we enjoy learning about new things and meeting new people, and participating in spirited debates.

Quick Navigation

User Menu

Steve Williams
Site Founder | Site Owner | Administrator
Ron Resnick
Site Co-Owner | Administrator
Julian (The Fixer)
Website Build | Marketing Managersing