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Old 28th September 2013, 11:38 PM   #231
1audio is offline 1audio  United States
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I looked into the predistortion stuff. Its interesting but seems to be focused on reducing IM on cell systems. That is a very different problem and they are using 10 and 12 bit ADC's not 24 bit ones. if you have a more relevant link I'm interested.
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Old 29th September 2013, 12:19 AM   #232
CG is offline CG
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I apologize for not having any useful links immediately.

Mostly, I have dealt directly with the guys doing this work. I'm not sure how public the details are, but I'll try to find out. It's true that all of the work I'm familiar with is centered around much higher frequencies than audio, but I'm told the problems are very similar.

I'll see what I can find out.
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Old 29th September 2013, 10:32 PM   #233
CG is offline CG
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I will still pursue asking the experts, but here is a paper that speaks in generalities about some approaches to digital predistortion techniques.

http://www.ece.rochester.edu/~sterling/icassp2007.pdf

There also is another approach, based on the idea that the test signal is pretty much deterministic, or could be made so.

Imagine that you take one of your high performance audio oscillators, and passively filter the harmonic output. In theory, harmonics will be buried well into the test system noise. So, if you apply that signal to your ADC system, ideally you should see nothing but the test tone. If you do, great. If there's other spurii in the results, these can be cancelled mathematically in the output. Are the tones gone? No, but they aren't part of the measurement. This is similar in concept to normalizing or calibrating amplitude response of a network analyzer. In that case you are not changing the nature if the applied signal, but instead are normalizing the results.

If this process is automated, it can be run at a host of levels and frequencies, giving an entire calibration table for the system. I think this is how the Agilent analyzers calibrate for X-parameter measurements.

That make sense? Why not use the computational capabilities of the control computer to help simplify measurements? The whole process could be used for both the generator side as well as the analyzer side. Done well, the generator could be pre-distorted to be essentially perfect, since you know what you want the output to look like - just add exactly the same level and exactly opposite in polarity tones to cancel the undesired products. Computational feed-forward, if you like.

Many of these ideas were already discussed, albeit in analog form, in the uber low distortion oscillator thread. I'm just suggesting getting the computer to do all the heavy lifting.

Last edited by CG; 29th September 2013 at 11:01 PM.
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Old 3rd October 2013, 12:20 PM   #234
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Hi Frex!
Tell me please, can you sell was built and debugged device, or just DIY kit?
How good is your ADC for high end audio or is it better to use for measurements?

Best
Igor
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Old 4th October 2013, 07:27 PM   #235
Frex is offline Frex  France
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Hello Igor,

I only sale bare circuit board (or only with CPLD programmed), you must get others parts by yourself.
Of course, i also provide design files to build it without issue.
You need some skill to solder SMD parts, but nothing very difficult
The AA5381 ADC has been designed to fit very well as measurement tool,
but you can of course use it as high-end audio recorder.
Regards.

Frex
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Old 4th October 2013, 08:21 PM   #236
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Quote:
Originally Posted by Frex View Post
Hello Igor,

I only sale bare circuit board (or only with CPLD programmed), you must get others parts by yourself.
Of course, i also provide design files to build it without issue.
You need some skill to solder SMD parts, but nothing very difficult
The AA5381 ADC has been designed to fit very well as measurement tool,
but you can of course use it as high-end audio recorder.
Regards.

Frex
Hi Frex!
Well, may be should recollect my youth and get a huge soldering iron! Besides this will take time and order the the other the elements (unfortunately in my country, this may not be quite simple). If I do not find a suitable device for my purposes, I will turn to you. Although it would be great to get the finished product.
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Old 9th October 2013, 05:21 PM   #237
Frex is offline Frex  France
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Hello Igor,

I understand. If you are really interested by finished one, and your not able to get parts,
i can sale you mine. So, i could build another one for me in my spare time...
Just send me a PM for that.
Regards.

Frex
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Old 13th October 2013, 10:00 AM   #238
DDriver is offline DDriver  Ukraine
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Hi, Frex!
The oscillator PCB are still available ? I am in for one board.

Greeting.
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Old 13th October 2013, 04:15 PM   #239
Frex is offline Frex  France
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Yes DDriver,
some bare PCB of EOSC10kV2 oscillator are available for sale.
Price is 25 including worldwide shipping in priority letter.
I only accept Paypal payment, and a full design folder of the design
is send by e-mail as soon payment done.
Regards.

Frex
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Old 21st October 2013, 09:54 PM   #240
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Quote:
Originally Posted by Frex View Post
Hello Igor,

I understand. If you are really interested by finished one, and your not able to get parts,
i can sale you mine. So, i could build another one for me in my spare time...
Just send me a PM for that.
Regards.

Frex
Hello Frex!

And what about my question?
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