Low-distortion Audio-range Oscillator

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#3,944
Samuel Groner said:
The "flat top" window is the best to use for THD measurements as it gives the lowest (IIRC a fraction of a dB) amplitude error of all windows available in the SYS-2722. It has poor side-lobe behaviour, but that's no issue as the dynamic range is low after the notch filter.

Samuel
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Hi Samual, --

thank you for giving us a window setting we can have confidence in.

David and Demian.... do you have ability to use Flat Top or rectangle or 'none' ??If so, would you repeat your tests with Flat Top?

THx-
 
#3,945
Drums had too short a range David, so they had to use smoke signals.

I guess you then, for arguments sake say the father of modern
digital communications are Samuel F. B. Morse, along with
Joseph Henry and Alfred Vail. Morse profited heavily from
it, I don't know aobut Henry and Vial. The Morse family used
to own Pebble Beach, CA.

Any of us could have purchased it all right after Pearl Harbor as nothing
would have, could have stopped the invasion of Japaneese forces.

There were sightings off the coast then. Rumors of a sub breaking up
south of there and bombers crashing in the Los Padres National Forest.
It is so desolate they still find WWII lost planes in there.

The answer is "42". Please bring your towel.
Somewhere in there is a lost gold mine and I think a silver mind
that has never been rediscovered.
 
#3,946
RNMarsh said:
Hi Samual, --

thank you for giving us a window setting we can have confidence in.

David and Demian.... do you have ability to use Flat Top or rectangle or 'none' ??If so, would you repeat your tests with Flat Top?

THx-
Click to expand...

Well I looked around but my oscillator seems to be missing.

Yes ARTA has FlatTop.

I also have SpectraPlus and see no disagreement there.



I posted a demonstration of that yesterday of the 339A

Noticeable but not much difference. Agrees with the table I linked to.
 
#3,948
Read it carefully. Measuring random noise is the discussion. Measuring discrete tones is what its normally targeted at. The correction factors are for noise.

I have a Wavetek FFT that has a noise measurement mode (in rtHz) that I use. Anything else has too many ways for confusion and mistakes.
 
#3,949
1audio said:
Read it carefully. Measuring random noise is the discussion. Measuring discrete tones is what its normally targeted at. The correction factors are for noise.

I have a Wavetek FFT that has a noise measurement mode (in rtHz) that I use. Anything else has too many ways for confusion and mistakes.
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Yes I know it for noise measurements. Richard is getting change on both. If a noise correction factor changes the tone as well something is wrong with the AP.
 
#3,950
From what I've read up on FFT what's in the bins is pile of noise and what ever has the greatest power, the signal, stands up more when the power in the bin is squared.
Why would the signal power be effected as much as it is on the AP by changing windows?
 
#3,955
RNMarsh said:
Some of the choices.... wider filtering would increase noise level on data display:

Click on these and blow them up to read.

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THx-RNMarsh
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I don't get what your pointing to. You stated in an earlier post you are seeing 6 to 9dB difference between flattop and hann. That's way too much and what you have above supports that. Therefore something is wrong.
 
#3,957
davada said:
I don't get what your pointing to. You stated in an earlier post you are seeing 6 to 9dB difference between flattop and hann. That's way too much and what you have above supports that. Therefore something is wrong.
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I said also that the average level difference is 4-5dB. Thats after tweeking the sample rates and steps et al. That seems realistic from what I read.
However, which is the most accurate one for measuring single sine wave for harmonic level.... Hann? As you and Demian are using? Or, A-P's Flat Top as I was suggested to use by A-P and is stated in their literature I showed above. and as Samuel seems to suggest using as well for amplitude accuracy. I think I will stick to using what A-P says to use. So there will be data difference between us if you dont want to use Flat Top Windowing.

I would need the 725D to be very different from the A-P before spending money to see if there is a problem with the A-P. When I had the 725D with me and compared, they agreed.

THx-RNMarsh
 
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#3,958
RNMarsh said:
I said also that the average level difference is 4-5dB. Thats after tweeking the sample rates and steps et al. That seems realistic from what I read.
However, which is the most accurate one for measuring single sine wave for harmonic level.... Hann? As you and Demian are using? Or, A-P's Flat Top as I was suggested to use by A-P and is stated in their literature I showed above. and as Samuel seems to suggest using as well for amplitude accuracy. I think I will stick to using what A-P says to use. So there will be data difference between us if you dont want to use Flat Top Windowing.

I would need the 725D to be very different from the A-P before spending money to see if there is a problem with the A-P. When I had the 725D with me and compared, they agreed.

THx-RNMarsh
Click to expand...

Okay then get Demian to use flattop then.
 
#3,959
davada said:
Richard here us info from Bruce himself.

AP High Performance Audio Analyzer & Audio Test Instruments : Service & Support

AP High Performance Audio Analyzer & Audio Test Instruments : Service & Support

You may have to add the correction factors in manually according to this. However this is for a different model.
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I've read this before. Interesting.. however, I dont really care about the noise level shifts with Windowing and A-P's approach to measuring. I accept it and would only need to get into it if I wanted to know the real noise level. But there are easier ways to measure wide band noise than deriving it from FFT/windowing etc. A more direct measure is useful. This only leaves the 'true' level of the harmonics to know and be certain of. After this, all will go smoothly.

THx-RNMarsh
 
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