In another discussion, I was challenged on why someone might use a high frequency tone such as 24 KHz (for 48 KHz sampling) to test for jitter. I explained that due to the way jitter works in that it creates sidebands that are proportional to source frequency +- jitter frequency, it is indeed possible to have audible jitter distortion even though the source tone/music itself is ultrasonic.
To demonstrate this, I used the Adobe Audition software's FM synthesis to create a scenario around this. I used a 24 Khz tone at -2dbfs (same level Paul Miller uses in his jitter tests) . I then added a jitter component at yet another ultrasonic frequency of 21 Khz. Here is the result: (you may want to right click and save the file locally and then playing it, If you don't do this, you may want to wait a few seconds for it to load before hitting the play button) http://www.whatsbestforum.com/tmp/jitter-62-2.wav
The distortion you are hearing is one million times lower than the 24 Khz tone at -66db yet it is quite audible. For grins, we can lower the music/excitation tone down by 7db, for distortion products at -70db: http://www.whatsbestforum.com/tmp/jitter-70-9.wav. Still readily audible on my laptop’s tiny speakers.
Let’s go down to -80db, with the primary tone now at -20db: http://www.whatsbestforum.com/tmp/jitter-80-20.wav. What you are hearing now is at the levels of measured jitter of about 2.5ns. I can still hear them without resorting to headphones.
Note that since jitter can have many components, frequencies and amplitude, there is no one sound that represents jitter. So this is just a sample, albeit an interesting test case.
To demonstrate this, I used the Adobe Audition software's FM synthesis to create a scenario around this. I used a 24 Khz tone at -2dbfs (same level Paul Miller uses in his jitter tests) . I then added a jitter component at yet another ultrasonic frequency of 21 Khz. Here is the result: (you may want to right click and save the file locally and then playing it, If you don't do this, you may want to wait a few seconds for it to load before hitting the play button) http://www.whatsbestforum.com/tmp/jitter-62-2.wav
The distortion you are hearing is one million times lower than the 24 Khz tone at -66db yet it is quite audible. For grins, we can lower the music/excitation tone down by 7db, for distortion products at -70db: http://www.whatsbestforum.com/tmp/jitter-70-9.wav. Still readily audible on my laptop’s tiny speakers.
Let’s go down to -80db, with the primary tone now at -20db: http://www.whatsbestforum.com/tmp/jitter-80-20.wav. What you are hearing now is at the levels of measured jitter of about 2.5ns. I can still hear them without resorting to headphones.
Note that since jitter can have many components, frequencies and amplitude, there is no one sound that represents jitter. So this is just a sample, albeit an interesting test case.