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Old 1st May 2013, 06:36 PM   #2551
davada is offline davada  Canada
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If there is going to be an a DSP involved why not just use one convertor. Store the period of a single cycle and sum it with the next cycle. This can be done recursively for any number of cycles. The output can be any convenient audio format.

Or just do what the 725 does and output that to a convenient audio format rather than reconstructing the signal and analog processing.

LT has a app note for this.

Look at figure 4. This can be modified to do the job.

http://cds.linear.com/docs/en/lt-jou...d_1100_Mag.pdf
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Old 1st May 2013, 07:54 PM   #2552
RNMarsh is offline RNMarsh  United States
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That could work as well. This sort of thing is the natural next step for a hyper-low distortion test system.

The Panasonic VP-7722A has just arrived to see what it's potential is and how well it works.and what is the design used. has great specs, uses DSP etc.
[>-140dB 2H rejection spec. THD <.0002% spec. Designed for to be fully automated for production testing of 10 parameters or more]

Thanks,
Richard

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Old 1st May 2013, 08:36 PM   #2553
RNMarsh is offline RNMarsh  United States
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The VP-7722A is similar to the ShibaSoku AD725D in THD resolution (using its own generator output to it's 7722 analyzer input displays a THD level of .00005%. So thats a good beginning. Have to look at the monitor port residuals with FFT. Measures individual harmonics like the 725 does. It also does IM and a host of measurements.... might be the one for you guys to find before prices go thru the roof on it. I paid $1k for it on eBay. I had found the 725D on eBay a microsec after it was put there asking only $450 and snatched it up. Later, I saw a refurbished 725d on another site going for $12K ! Good deals do exist from time to time.]

-RNM

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Old 2nd May 2013, 04:51 AM   #2554
1audio is online now 1audio  United States
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I'm sure its a really nice bench tester. Its new enough that it will have the sharp low pass filter necessary to measure distortion on digital sources. Since its defined by numbers and the Japanese have an obsession with performance execution it will be a really good instrument.
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Old 2nd May 2013, 05:38 AM   #2555
1audio is online now 1audio  United States
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Quote:
Originally Posted by davada View Post
If there is going to be an a DSP involved why not just use one convertor. Store the period of a single cycle and sum it with the next cycle. This can be done recursively for any number of cycles. The output can be any convenient audio format.
This is what the melt noise is doing on the QA400. Unfortunately the trigger/clock must be precisely synchronized with the signal or both the signal and the noise "melt". If the QA400 had a continuous mode it would be possible to lock an external oscillator.
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Old 2nd May 2013, 02:03 PM   #2556
davada is offline davada  Canada
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Quote:
Originally Posted by 1audio View Post
This is what the melt noise is doing on the QA400. Unfortunately the trigger/clock must be precisely synchronized with the signal or both the signal and the noise "melt". If the QA400 had a continuous mode it would be possible to lock an external oscillator.
I noticed that with the melt. It took the signal down too.
Needs a little work.
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Old 2nd May 2013, 02:06 PM   #2557
davada is offline davada  Canada
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Hi Demian,

Is windows audio capable of any sample rate or the just the common audio sample rates?
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Old 2nd May 2013, 02:21 PM   #2558
1audio is online now 1audio  United States
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Quote:
Originally Posted by davada View Post
I noticed that with the melt. It took the signal down too.
Needs a little work.
If you use it in loopback the signal should not change. Any synchronous component will be reinforced. Any noise/randomness will get reduced. It does seem to work for me.
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Old 2nd May 2013, 02:24 PM   #2559
1audio is online now 1audio  United States
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Originally Posted by davada View Post
Hi Demian,

Is windows audio capable of any sample rate or the just the common audio sample rates?
Depends- The windows sound engine supports a standard list of sample rates and resamples everything to the default rate of your system. Its not a particularly good resampler and should not be used in any measurement process. If you use something like ASIO you can go around the sound engine somewhat, if your soundcard driver and application supports ASIO.
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Old 2nd May 2013, 03:00 PM   #2560
davada is offline davada  Canada
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Originally Posted by 1audio View Post
Depends- The windows sound engine supports a standard list of sample rates and resamples everything to the default rate of your system. Its not a particularly good resampler and should not be used in any measurement process. If you use something like ASIO you can go around the sound engine somewhat, if your soundcard driver and application supports ASIO.

Will ASIO support any sample rate?
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