(Not a) good explanation of jitter in TAS
Reply #129 – 2009-08-03 16:54:43
We are considering the creation of an ABX jitter test that could be posted on this forum. The test would allow comparisons between a jitter-contaminated track and an original track. We will keep this forum posted on our progress. That seems like a coincidence, since I don't expect you have written those four paragraphs within 3 minutes. I'm looking forward to your proposal. Yes indeed, I read your post after I posted. Here is what we could do with the equipment we have (comments and suggestions welcome): Jitter ABX: We have low-noise 96 kHz 24-bit recordings that are known to have been made with very low-jitter A/D converters. We can use these as test material. We will also apply the same procedure to a 10 kHz sine wave test tone (to show jitter sideband amplitudes on an FFT analysis). We have D/A converters in-house that will reproduce these tracks without any significant jitter artifacts (sidebands at least 135 dB below the music signal or test tone). We have an A/D converter in house that allows us to switch jitter attenuation on and off. When jitter attenuation is on, jitter-induced sidebands will be at least 135 dB below the music signal. We will use the A/D to apply jitter modulation to the clean analog audio reproduced by the "jitter free" D/A converter. Two versions will be created; one "jitter free" and one with added jitter. The result will be two 96 kHz 24-bit digital files (one with encoded jitter artifacts and one without). We will use one of our Audio Precision 2722 Test Systems to generate the jitter signal. We can generate sinusoidal, square and/or random jitter functions of varying amplitude (but must limit the choices if we want to get anything done). I suggest the use of the foobar ABX test plug-in, but careful attention must be paid to the following: 1) Jitter performance of the playback DAC 2) Distortion performance of the playback DAC 3) Data path from foobar to the DAC 4) Playback levels should be documented. 5) Playback equipment should be documented CD player ABX: Capture the output of a CD player using a "jitter free" A/D with precisely normalized gains. Capture the output of the same CD player through a "jitter free" D/A feeding the same A/D. Publish original track and captured CD player track, and the captured "clean track" for download and ABX comparison. All three tracks would be 44.1 kHz 16-bit. Play a 10 kHz TPDF -20 dB FS tone through both chains and capture the results for FFT analysis (to confirm presence of sidebands). Measure frequency response of both chains. The CD player test is much simpler and we may want to start with this. Comments and suggestions welcome please!