 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
65.19.76.104
In Reply to: RE: JetPLL™ jitter reduction technology posted by fmak on February 16, 2012 at 07:51:15
"It is frequencies well below 100 Hz (10 Hz) that count."
I don't think so.
10 Hz is in the range corresponding to flutter. The best tape transports have far more speed variation in this range than one would see from any digital and yet are deemed to sound good. With digital, it's the higher frequencies that count where the sidebands are far enough away from the music tones that they won't be masked.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Follow Ups:
Tony,
Audio related jitter error is most prevalent below 10Hz and is best tested at 1Hz. Fred is correct about this.
If you look at the new breed of oscillators for audio from Crystek you will see they are testing to 10Hz in their graphs. This is good, but when tested to 1Hz these look good but not great.
~~~~~
Fred actually the Jetpll is pretty well respected. It is still what it is and really does not approach fixed XO performance, but it really made a big impact in low cost Pro gear, which before that was dreadful.
Thanks
Gordon
J. Gordon Rankin
Yep, I was off by about 20 dB.
A quick calculation. The time between symbols in SPDIF (biphase modulation) at 96/24 stereo is about 100 nsec. (1/(96000*24*2 *2)). This means that an SPDIF signal having peak jitter of 25 nsec can be reliably decoded.
The peak flutter of a Studer A820 at 15 IPS is 0.04%. The period of digital audio samples at 96 kHz is about 10,000 nsec. To achieve comparable jitter performance to this flutter performance the jitter at a DAC would need to be kept below 4 nsec. So it looks like my statement is only correct if an SPDIF DAC clock recovery circuit reduces the received jitter by about 20 dB down in the flutter range. (The AES flutter measurement standard weighs flutter with a filter centered on 4 Hz, rolling off 6 dB per octave above and below.)
The PLL will follow the source clock below its cutoff. If we assume the AES perceptual weighing is correct the bandwidth of the PLL must be kept well below 1 Hz for my statement to be correct. This obviously is not covered by the JetPLL specification, as fmak correctly pointed out.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Read up on phase noise.
"Read up on phase noise."
I have. That's why I made my comment about tape flutter vs. digital jitter.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Then you have not understood the effect of low freq noise on jitter.
Please explain the difference between low frequency noise on the clock signal at a digital to analog converter and how it differs from low frequency noise on the linear motion of tape over a playback head on its effect on the resulting audio signal.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
Go to diyhifi.org and serach for Jocko and George Hi Fi's posts.
There is no direct correlation between analog and digital audio when it comes to jitter, Many PLLs deal with high freqs but not low ones.
You didn't answer my question, presumably because you didn't understand it. I made the question as clear as possible, so I don't believe there is any more point to this discussion.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
I have shown you how to get answers.
As you must know by now, I am not here to write 1000 words pieces for inmates who say they have intimate knowledge of digital audio, and then enter into some circumnavigating debate on side issues.
I was hoping you would give us the answers in your own words, so that the skeptics here can see if you know what you are talking about and not just blowing smoke.
Tony Lauck
"Diversity is the law of nature; no two entities in this universe are uniform." - P.R. Sarkar
If you are not prepared to do your own homework, who is blowing smoke?
"You didn't answer my question, presumably because you didn't understand it. I made the question as clear as possible, so I don't believe there is any more point to this discussion."
Tony,
This is par for the course... He still never answered why he is putting a 3 amp slow blow fuse in a device that should draw well less than one amp?
:)
Post a Followup:
| FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
||||||||||||||
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]