JISCO Jitter reduction - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 22nd October 2003, 05:13 PM   #1
diyAudio Member
 
Tieftoener's Avatar
 
Join Date: Nov 2002
Location: Coastal AL
Default JISCO Jitter reduction

OK, I've seen a few posts on audioasylum about this thing, but have been unsuccessful in finding information on this forum. Anybody ever heard of it, or tried it? The reviews I've read are pretty convincing... but not enough to spend $500 on it.

I'm wondering if the amazing minds over here could possibly reverse engineer the concept... The concept makes sense to me, but I just can't figure out how passive device can first scramble the jitter, and then proceed to modulate it. How does one 'isolate' jitter? It's not really "part" of the signal, but rather, it "IS" the signal. I'm confused...

Perhaps this is the answer to the jitter problems of SPDIF ???

www.jitter.de/english/jisco.html

Please advise
__________________
Tieftoener -- You're ears can sense a movement in air that causes your eardrum to move less than 1/10th of the diameter of a Hydrogen atom! Don't abuse the one of the most amazing organs your Creator gave you!
  Reply With Quote
Old 22nd October 2003, 05:41 PM   #2
diyAudio Member
 
Join Date: Oct 2003
Location: The Lab
I would say one of these things would be fairly easy to build yourself, at a very small fraction of 500$.

My guess is you need a 40 MHz clock generator (derived from the 25nS delay time in the datasheet), a 74HC74 flip flop, and a 74HC04 for input / output signal conditioning.

Total cost of parts: 3-4$ plus the nice box and BNC plugs.
  Reply With Quote
Old 22nd October 2003, 07:32 PM   #3
diyAudio Member
 
Tieftoener's Avatar
 
Join Date: Nov 2002
Location: Coastal AL
I figured it would be easy to do...

Until now, I thought that it was a passive device. But, now I see that there is an "external power supply" in the spec sheet discription. This makes me feel much better.

Lars, could you elaborate a little more on the application of the flip-flop? I'm assuming he's just doing amplitude modulation with a summing circuit...

I still don't understand how the jitter is "isolated" to be modulated. The whole signal would be modulated from what I can see, and while the PLL will have the high frequency noise reduction to cancel out the 40MHz, the (primarily large) 10kHz jitter would still pass through. What am I missing...???

Thanks,
__________________
Tieftoener -- You're ears can sense a movement in air that causes your eardrum to move less than 1/10th of the diameter of a Hydrogen atom! Don't abuse the one of the most amazing organs your Creator gave you!
  Reply With Quote
Old 22nd October 2003, 07:44 PM   #4
diyAudio Member
 
Join Date: Oct 2003
Location: The Lab
From the description it seems clear, that the principle of this device is:

'If you can't remove the jitter, add some instead.'

And it might have an effect, because the jitter is not modulated with music signal, but overloaded with 'pink time noise', resulting from the modulation between the 40 MHz and the asyncronous SP/DIF signal.

I don't know for sure if it works this way, but it appears so, if you read between the lines of the data sheet.

It's a little bit like a Triode amplifier, the harmful (high order) distortions are masked by 10 times louder nice sounding (low order) distortions.

You might get out of the 'phonebooth effect' with this unit, however i don't think it is the solution for a wide and precise soundscape. For this you need to remove the jitter all together (which is very possible).
  Reply With Quote
Old 22nd October 2003, 09:51 PM   #5
Banned
 
Join Date: Feb 2002
Location: As far from the NOSsers as possible
Default I agree with part of what he says......

The part about you have to have low jitter at the DAC.

Even if his "decorrelates" the incoming signal, the PLL in the RX will generate its own anyway.

The only real way to do this is with a secondary PLL with a very stable VCXO as its reference.

Takes a few flip-flops, a good op-amp, clean VCXO, knowledge of PLLs..............

Jocko
  Reply With Quote
Old 29th October 2003, 11:50 PM   #6
Wim M is offline Wim M  Netherlands
diyAudio Member
 
Join Date: Oct 2003
Location: Groningen
For those who can make something of it: on the Jisco website (www.jitter.de) you can find a picture of how the device looks from the inside. It's in the pdf-file 'jitter artikel II' marked as 'new', top-right on the main page. (The text in that document is a nice explanation of the jitter phenomenon, but only in German.)
  Reply With Quote
Old 30th October 2003, 09:15 AM   #7
diyAudio Member
 
Join Date: Oct 2003
Location: The Lab
Very interesting ...

I found the Quartx oscillator on Google, it appears to be a standard 100 ppm TTL oscillator. Costing Ä1.45 = $1.75.

http://www.hofstaedtler.at/sonder/oszillatoren.htm

Two chips for SP/DIF signal recovery, presumably 74HCU04 or 74HC04, and the GAL 16V8 (www.latticesemi.com) for flip-flopping. (These programmable devices are often used only with the intent to improve the mystification factor, hence stopping diy'ers from copying the circuit. It is a programmable Logic Array, but the fact is, the device is so simple, that the program can pretty much only be used to direct input signals to the 8 internal logic gates / flip flop's - no big deal).

Total cost of active parts ... around 7-8 US$
Plus the nice box still .. )
  Reply With Quote
Old 30th October 2003, 11:28 AM   #8
Banned
 
Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Send a message via Yahoo to Elso Kwak
Cool Jisco Jitter decorrelator

Hi Wim,
for more information see:
http://l2.espacenet.com/espacenet/vi...b&LG=en&DB=EPD
and
http://l2.espacenet.com/espacenet/bn...+10006880A1+I+

Persononally I believe any jitter reduction device should be placed after the digital inputreceiver and also after the digital filter, if used, not before.
Unfortunately I did not find how exactly the Jisco works but I presume just as my Asynchronous Reclocker with a 40 MHz oscillator and a few flip-flops.
http://home.student.utwente.nl/f.s.b...-schematic.gif
and
http://www.geocities.com/react_71/audio/
(schematic will be soon on Pedja's site)
The decorrelation is a nice theory why the asynchronous reclocking improves the sound.

Still better is, I believe, to avoid the SPDIF interface all together using I2S direct or a one-box player.
http://www.diyaudio.com/forums/showt...220#post249220
  Reply With Quote
Old 30th October 2003, 12:12 PM   #9
diyAudio Member
 
Join Date: Oct 2003
Location: The Lab
Elso i agree with you completely!
  Reply With Quote
Old 30th October 2003, 05:54 PM   #10
diyAudio Member
 
Join Date: Oct 2003
Location: The Lab
You can also remove jitter from the SP/DIF line in another way:

1..Mount the ref clock in the DAC (rather than the transport).
Now the DAC has low jitter clean clocking.

2..Sync the transport with a coax running from the DAC to the
transport. Add 75 Ohms resistors on in-a nd out put of cable to avoid standing waves.

It works great IF your transport and DAC run on the same frequencies, like 11.2896 MHz ( the most common for DAC's) or 16.9344 MHz if your DAC uses the YM3623 receiver chip. (The receiver chip decides the operating clock frequency of the DAC) All Crystal (Now Cirrus Logic) and Philips receivers run 11.2896 MHz.

In some cases it works also when the transport and DAC run on different clock frequencies, but that is the twilight zone. Be careful, this should only be attempted by experienced diy'ers.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
generate jitter test signal and measurign jitter using AP2? BJAMR Digital Source 11 1st November 2010 02:07 PM
Hum reduction ideas (again) zigzagflux Tubes / Valves 2 26th November 2008 03:53 AM
Data Jitter Versus Electrical Jitter? 300_baud Digital Source 8 16th July 2004 07:59 PM


New To Site? Need Help?

All times are GMT. The time now is 01:29 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2