This is excerpted from a longer article available here:
https://uk.yamaha.com/en/products/contents/proaudio/docs/audio_quality/05_audio_quality.htmlaudibility of jitter:Assuming a 0dBfs sine wave audio signal with a frequency of 10kHz as a worst case scenario, a jitter signal with a peak level of 5ns will generate a combined A/D and D/A jitter noise peak level of:
EA/D+D/A = 20.log(2.5.10-92.π.10.103) = -64dBfs
When exposed to listeners without the audio signal present, this would be clearly audible. However,
in real life jitter noise only occurs with the audio signal in place, and in that case masking occurs: the jitter noise close to the audio signal frequency components will be inaudible, so the average audio signal’s spectrum will mask a significant portion of the jitter noise.
Note that the predicted level is the jitter noise peak level generated by 0dBfs audio signals. In real life, the average RMS level of jitter noise will be lowered by many dB’s because of the audio program’s crest factor and the system’s safety level margins used by the sound engineer. Music with a crest factor of 10dB played through a digital audio system with a safety level margin of 10dB will then generate
jitter noise below -84dBfs.The audibility of jitter is a popular topic on internet forums. Often a stand-alone digital mixing console is used in a listening session, toggling between its internal clock and external clock. In these comparisons it is important to know that such comparison sessions only work with a stand-alone device. If any other digital device is connected to the mixer, then clock phase might play a more significant role in the comparison results than jitter.
In uncontrolled tests, many subjective and non-auditory sensations have a significant influence on the result.
In multiple clinical tests, the
perception threshold of jitter has been reported to lie between 10 nanoseconds(* 5U) for sinusoidal jitter and 250 nanoseconds(* 5V) for noise shaped jitter - with actual noise shaped jitter levels in popular digital mixing consoles being below 10 nanoseconds.
