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Old 29th January 2013, 11:23 AM   #1621
Telstar is offline Telstar  Italy
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Originally Posted by RNMarsh View Post
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 think that's the case. They used a notch filter maybe?
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Old 29th January 2013, 08:49 PM   #1622
RNMarsh is offline RNMarsh  United States
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Originally Posted by Telstar View Post
I think that's the case. They used a notch filter maybe?
No notch then but they do now.
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Old 30th January 2013, 06:15 AM   #1623
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I am using an ESI Juli@ card to bring the data into my PC. I use Praxis as my primary go to software solution, mostly because I have it and know how to get a lot from it. However HPW-works or Arta or others are similar. I don't think any of them are nuts enough to include 16M point fft's.
Well, HpW-Works supports up to 32M FFT using a 64Bit MS OS (8 GBytes system memory) and has included the required high performance FFT Windows functions! The calculation is internal done by 64 & 80 bit float.

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The QA400 uses the Cirrus CS4272 CS4272 : 114 dB, 24-Bit, 192 kHz Stereo Codec which seems to be pretty good and a good value but not in the same league.
This exactly the point! In the old days good sound card as Turtle Beach Tahiti went down to DC and at this time the Sound Blasters using Codec's where no value. For measurement the source or converter should deal in a higher league!

Currently I have to time to deal with such HW... This HW should also deal with input & output gain / attenuation / load (Pete already asked ).

There are also some new ADC/DAC on the horizon as Arda Technologies - Home...


HpW
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Old 30th January 2013, 07:37 AM   #1624
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No notch then but they do now.
I'm still confused about what AP model you're talking and what your exact setup is--the top-notch models System One, System Two and SYS-27xx surely have an analog notch filter which you can route ahead of the ADC. If you're feeding the ADC with the input signal directly don't blame anyone else for unreliable results... An ordinary ADC is good down to -100 dB THD, a recent high-performance one perhaps to -110 dB.

Samuel
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Old 30th January 2013, 08:02 AM   #1625
RNMarsh is offline RNMarsh  United States
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Originally Posted by Samuel Groner View Post
I'm still confused about what AP model you're talking and what your exact setup is--the top-notch models System One, System Two and SYS-27xx surely have an analog notch filter which you can route ahead of the ADC. If you're feeding the ADC with the input signal directly don't blame anyone else for unreliable results... An ordinary ADC is good down to -100 dB THD, a recent high-performance one perhaps to -110 dB.

Samuel
A-Prec Sys one. The generator has lower thd/harmonics than is shown by its own FFT. I had not heard about that before. It doesnt look like a notch is used.... but attribute the problem to poor adc/dac of the era.

I see the data from the newest AP and it looks like a notch is used. I didnt get that with the system One (dual domain model). So, now, I want to see an FFT that gives more accurate results without buying a newer A-P ($$$). I need a better ADC. I was dissapointed that newest ADC's can not be used straight into them and not be a lot better than -100.... So, now am looking for a notch filter to make/buy/steal to go with a couple of adc i recently acquired.

Meanwhile, I bought a ShibaSoku AD725D distortion analyzer. That with an excellent sine wave source has made the whole ADC issue mute. Almost. I still want to get as low Harmonic measurement as I can using an ADC with a notch filter to see harmonics beyond the 5th measured by ShibaSoku. I should be able to hook up, as Damian says, to the instrument with any ADC and get accurate data on harmonics but I havent seen that happen yet. ??

Yes, it looks like the -100 is close to the limit straight in, as you say. And, then drop 5-10 dB from the max input level. So we have a real 90dB range to work with for accurate measurements use... which makes me think John Curl is correct... we (he) can design analog which is still better than what digital can do.

Thx for your input to my saga on this.... waiting on a pcb for a twin-t filter now. -RNMarsh

Last edited by RNMarsh; 30th January 2013 at 08:08 AM.
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Old 30th January 2013, 08:35 AM   #1626
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Dual-Domain System One surely can route the notch filter ahead of the ADC. I've just run a measurement on the one we have, and I see the harmonics at/below -120 dB (1 kHz/+10 dBu).

Setup as follows:

* Analog Analyzer Function Reading set to "THD+N Ratio"
* Digital Analyzer Source set to "Anlr Rdg Ratio"

Samuel
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Old 30th January 2013, 01:14 PM   #1627
davada is offline davada  Canada
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Originally Posted by HpW;3348231
There are also some new ADC/DAC on the horizon as [url=http://www.ardatech.com
Arda Technologies - Home[/url]...


HpW
That's been up there a long time and I haven't seen anything come of it.
I see they removed their store.
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Old 30th January 2013, 02:02 PM   #1628
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That's been up there a long time and I haven't seen anything come of it.
I see they removed their store.
24 bit resistor ladder DAC, interesting they don't mention factory calibration and/or any trimming.
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Old 30th January 2013, 05:10 PM   #1629
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Originally Posted by RNMarsh View Post
A-Prec Sys one. Thx for your input to my saga on this.... waiting on a pcb for a twin-t filter now. -RNMarsh
I agree with Samuel I have never seen an AP without a notch on the fundamental available.

Here's a simulator for you, Infinisim - Results. Probably beyond the budget.
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Old 30th January 2013, 05:29 PM   #1630
RNMarsh is offline RNMarsh  United States
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I have to stand by what i saw.... took it to another with newer AP model and compared.... they saw same thing. Either mine has an problem or that is the way it is made.
But, -120 isnt good enough anyway. Marginal. I'm looking for at least -130. -140 would be more useful.

BTW --just got a note - Victor hyper tuned a 1KHz oscillator that takes the H2 down to -150 ! That pretty much takes it out of the picture for my use !

Thx-RNMarsh

Last edited by RNMarsh; 30th January 2013 at 05:59 PM.
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