Lee Scoggins
Senior HTF Member
For regular CD (redbook) and high resolution digital audio, audio signals consist of (1) musical data in the form of one and zeros like computer data - the Y axis and (2) time code not like computers - the X axis.
Time code is the least understood. In 1992 some friends of mine and I worked on a Test CD for Chesky Records. We recorded some music with a digital interconnect between the ADC and the digital storage unit. We tried a very high jitter cable ($2) and a low jitter cable ($500). In preparation of a new audio test CD, I had an opportunity to conduct a blind test at the Atlanta Audio Society today.
What happens when the time code is off just a little bit?
Each music sample was exactly the same in musical data of a drum solo with increasing dynamics. Around 20 Society members were in attendance. We listened twice to each sample and no one was told which was the lower jitter sample. In this brief test, we found roughly five people felt that the first sample (high jitter) was more musical and around 15 preferred the lower jitter second sample. While not the last word in studies, this confirms our basic contention of the audibility of jitter.
We have also noticed that when we add an external master clock to our beloved Alessis decks, the jitter goes down from 200 picoseconds (yes, that small!) to 20 picoseconds (ps) and the music, particularly strings opens up to more detail. The image seems tighter and more musical.
We have discovered two scientific proofs of jitter. This is important for reproducing music since this time-based distortion
The first is by Julian Dunn of Nanophon:
http://www.nanophon.com/audio/jitter92.pdf
See Section 3.3 Audibility of Jitter. Here Julian finds that 20 ps should be the threshold of audibility on high frequencies.
The second paper is by Eric Benjamin and Benjamin Gannon presented in 1998 at the AES where audibility was discovered to 10 ns.
What is the value of all of this for music fans?
(1) Buy hardware that has lower jitter statistics. These can often be found in Stereophile and The Absolute Sound.
(2) For the best in sonic realism, purchase music that is produced by audiophile labels that use low-jitter recording chains.
This jitter also affects the production of the "glass master" used in the CD manufacture. I will comment on this in a later thread as I learn more of the details.
Think of it this way..."bits are bits when they arrive at the precisely right moment in time."
Do you have any experience with certain CD transports sounding better than others?
Do you believe in jitter's audibility?
Do you find Julian's paper to be valid?
Time code is the least understood. In 1992 some friends of mine and I worked on a Test CD for Chesky Records. We recorded some music with a digital interconnect between the ADC and the digital storage unit. We tried a very high jitter cable ($2) and a low jitter cable ($500). In preparation of a new audio test CD, I had an opportunity to conduct a blind test at the Atlanta Audio Society today.
What happens when the time code is off just a little bit?
Each music sample was exactly the same in musical data of a drum solo with increasing dynamics. Around 20 Society members were in attendance. We listened twice to each sample and no one was told which was the lower jitter sample. In this brief test, we found roughly five people felt that the first sample (high jitter) was more musical and around 15 preferred the lower jitter second sample. While not the last word in studies, this confirms our basic contention of the audibility of jitter.
We have also noticed that when we add an external master clock to our beloved Alessis decks, the jitter goes down from 200 picoseconds (yes, that small!) to 20 picoseconds (ps) and the music, particularly strings opens up to more detail. The image seems tighter and more musical.
We have discovered two scientific proofs of jitter. This is important for reproducing music since this time-based distortion
The first is by Julian Dunn of Nanophon:
http://www.nanophon.com/audio/jitter92.pdf
See Section 3.3 Audibility of Jitter. Here Julian finds that 20 ps should be the threshold of audibility on high frequencies.
The second paper is by Eric Benjamin and Benjamin Gannon presented in 1998 at the AES where audibility was discovered to 10 ns.
What is the value of all of this for music fans?
(1) Buy hardware that has lower jitter statistics. These can often be found in Stereophile and The Absolute Sound.
(2) For the best in sonic realism, purchase music that is produced by audiophile labels that use low-jitter recording chains.
This jitter also affects the production of the "glass master" used in the CD manufacture. I will comment on this in a later thread as I learn more of the details.
Think of it this way..."bits are bits when they arrive at the precisely right moment in time."
Do you have any experience with certain CD transports sounding better than others?
Do you believe in jitter's audibility?
Do you find Julian's paper to be valid?
