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Old 28th January 2013, 05:39 PM   #1601
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
You are bumping into the Crystal ADC's limits.

I have attached a plot of the same generator as above (KH4400) measured with the QA400. You can see the difference in the distortion floor. Other key tricks, you must get the frequency to be precise or the bins will miss. That's why I added the injection lock to the KH4400. Make sure the internal generator matches the frequency since that is what their software uses to determine the harmonics.

The QA400 software is a good start and will get useful results immedately. However if something like HPW-works were to support the hardware I would find that very helpful (hint!).
Hi Demian,

I raised the question of software dependency on the internal generator of the QA400 with Matt and he said all the software does on the FFT side is measure.

Unless explicitly set to use gen1 for THD calculation then the SW just uses the highest
measured signal to calculate THD, THD+N.

I asked Matt if they could add in the option of specifying a frequency to use for THD calc
but it's not working the way I envisioned it. I also asked for an option to have markers track what they are placed on. If they can get this working then THD can be calculated on the markers used.
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Old 28th January 2013, 05:46 PM   #1602
davada is offline davada  Canada
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Hi Samuel,

If you are willing to share that, Mat at QuantAsylum is really open to suggestions and adding features to improve the software.
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Old 28th January 2013, 06:09 PM   #1603
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Telstar View Post
Weird, can somebody borrows you an AP?
Well, this is becoming a pattern. I had an A-P and I used the FFT in it and same thing! The FFT showed higher distortion than swept sine measurement from same instrument. I thought something was wrong with A-P and took it to Thailand for repair in October. Its still there. Maybe nothing is broken with it?!

So I started on the 339A and then the ShibaSoku and the QA400. Similar results. I think the A-P (earier version) didnt have the ADC/DAC precision available today. So, it read higher harmonics than the QA does. [But a lot of people used it and published the DUT results with the FFT.]

I can see the harmonic structure change (2nd relative to 3rd) as I lower/raise the input level to the QA400. So, I know I Must use a notch before it. That is my next step. I'd like to see QA make a variable notch filter... I hate making this stuff... so time consuming for the users. Note: QA spec's the -400 as a 105dB range. I need a lot better and the notch into the QA400 might do it for me.

Thx-RNMarsh

Last edited by RNMarsh; 28th January 2013 at 06:19 PM.
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Old 28th January 2013, 06:12 PM   #1604
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If you are willing to share that, Mat at QuantAsylum is really open to suggestions and adding features to improve the software.
Sorry, killed my post because I realized that I didn't read the one I was answering correctly.

I was saying that there are much better windows than the ordinary flat top one finds in standard FFT software. I'm using some of those disclosed here for critical work:

http://www.rssd.esa.int/SP/LISAPATHF...sis/GH_FFT.pdf

I'll need to install the QA400 on my new computer to get it up and running.

Samuel

Last edited by Samuel Groner; 28th January 2013 at 06:15 PM.
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Old 28th January 2013, 06:14 PM   #1605
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The FFT showed higher distortion than swept sine measurement from same instrument.
What do you mean by "swept sine measurement"? Did you use the FFT after the notch filter or with the direct analog input? And what distortion level are we talking about?

Samuel
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Old 28th January 2013, 08:46 PM   #1606
RNMarsh is offline RNMarsh  United States
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I mean like the way 339A measures or other non FFT instrument... all analog.
Direct analog input is used... without notch on fundemental.
Really low and near max level. Above 0.5 volts and below -90.
No complaint about windowing or FFT software at this time.... adc issue, i'm sure --- well, maybe sure.
Thx-RNMarsh

Last edited by RNMarsh; 28th January 2013 at 09:05 PM.
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Old 28th January 2013, 11:42 PM   #1607
davada is offline davada  Canada
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Quote:
Originally Posted by RNMarsh View Post
I mean like the way 339A measures or other non FFT instrument... all analog.
Direct analog input is used... without notch on fundemental.
Really low and near max level. Above 0.5 volts and below -90.
No complaint about windowing or FFT software at this time.... adc issue, i'm sure --- well, maybe sure.
Thx-RNMarsh
Hi Rick,

Do you mean swept tuned? That would be an analog spectrum analyzer.
Neither the 339a or the ShibaSoku are swept tuned. The 339a is direct and the ShibaSoku, after reading the patent paper, is a very clever approach to resolving harmonic distortion, typical of Japanese engineers. Sample the fundamental and reconstruct it at a fixed lower frequency so that fixed frequency filters can be used. It's not heterodyne as I thought but it's has similarities.
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Old 29th January 2013, 12:17 AM   #1608
RNMarsh is offline RNMarsh  United States
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I was thinking the A-P swept sine. But all analog is the meaning and not FFT adc. I Thought a 24/192 would be better than they are for this purpose..... I mean with -144 noise floor you would think it is better than it is with thd, too. Is the Analog Devices much better... looks great on paper... esp. thd at -60db. Its my current favorite for audio use. Thx-RNMarsh
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Old 29th January 2013, 12:39 AM   #1609
1audio is offline 1audio  United States
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The AKM 5394a is the best I have measured so far. Its possible the new one from ESS, 9108, could be better. Since the demo board is $450 I won't be finding out. I have an app note for bonding two AKM ADC's together to get a lower noise floor. The linearity on any of these is exceptional, especially considering the limited voltage range they have to work with.
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Old 29th January 2013, 01:05 AM   #1610
davada is offline davada  Canada
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Originally Posted by 1audio View Post
The AKM 5394a is the best I have measured so far. Its possible the new one from ESS, 9108, could be better. Since the demo board is $450 I won't be finding out. I have an app note for bonding two AKM ADC's together to get a lower noise floor. The linearity on any of these is exceptional, especially considering the limited voltage range they have to work with.

Hi Demian,

Can you post that app note?
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