To measure jitter, we use the same method that the Hi-Fi magazine Stereophile uses for their testing. An example of their measurement method can be seen here. The method is described in detail in this paper by Julian Dunn. The signal used is a 11025 Hz sinewave at -3 dBFS added to a square wave at 229 Hz at -90.3 dBFS. In Hexidecimal numbers, this signal translates to: “C000 C000 4000 4000 (x24) BFFF BFFF 3FFF 3FFF (x24)” repeated again and again.
When you examine the signal around the 11025 Hz peak, the peaks at 11025-n*229 Hz and 11025+n*229 Hz result from data-induced jitter. The peak-to-peak jitter can then be roughly, but only roughly, calculated from these peaks by the formula presented in Dunn's paper. Due to the limitations of analogue to digital conversion resolution and noise, the precision of this method is limited to a comparison and an estimate of the jitter content of around 40 ps (picoseconds peak-to-peak).
DAC 2004 and CD Players :: Measuring Jitter Performance
The total jitter is the sum of this value for all peaks. Adding up only the highest peaks gives a good estimate of the total amount of jitter. Based on this, here is a list of approximate jitter values:
DAC 2004 :: Very Near Ultimate Perfection
The image below shows the typical scenario using a CD Player and high quality DAC in the traditional way:
It is clearly evident that in this configuration the Jitter is worse than 500 ps.
The following image shows the typical scenario using a CD Player with a high quality clock upgrade, and whose external DAC is also slaved to the CD player, which is in principle the exact same scenario as above, only with a better clock. This is also the case when using a $10,000 transport with the best possible internal clock:
It is clearly evident that this configuration achieves less Jitter at about 170 ps.
Now we modify the cheapest CD Player we can get our hands on (in this case a JVC model) and use the external LessLoss Audio DAC 2004 in Digital Master Mode. In this way, the Master Clock is in the DAC and the CD player is connected via two cables: the typical S/PDIF Digital cable and a Digital Clock cable. The results would not differ if you used a $10,000 transport with the best possible drive mechanism or other exotic features such as Housing Metal from Mars, etc.:
You can clearly see that this configuration achieves the least possible Jitter at less than 60 ps. Due to noise resulting from the ADC conversion process, it is not possible using this method to make any judgement on anything less than around 50 ps.
However, to show what the absolute ideal case would look like, we have generated this simulation. It differs from reality in the following ways:
Again we stress that this last image does not reflect a physically measured case, but rather a case which would have less than ~30-50 ps jitter using the method described above, were it possible to measure the results in this way. We believe that the LessLoss Audio DAC 2004 is capable of this performance, using a customized, mass-produced CD player!