Using REW with the DATS hardware...

Brian Steele

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I've found a way to get REW to do impedance measurements using the DATS v2 hardware, but to get it to work a bit better, I need to be able to set the value for the measurement level higher than the apparent maximum of -3dB that can be set in the measurement dialog box. Is there any way to do this?
 

John Mulcahy

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That's a full scale signal in the digital domain, best check the various Windows volume controls to see if anything else along the path is reducing the level.
 

Brian Steele

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Ok, thanks John. I'll take a closer look. I just stumbled across this a day or so ago, when wondering if I could use REW directly with the DATS v2 hardware to take impedance measurements, rather than using the DATS software and then exporting the data and importing it into REW.

The other issue I'm running into is REW complaining that the input level is too low during the leads calibration sequence, but it seems to measure impedance correctly after that when I read the leads resistance level off of the generated graph and use that for subsequent measurements. See attached capture for example, which is a comparison of impedance measurements taken with REW and DATS software, using the same DATS hardware and speaker.
20180103-DATS vs REW.png
 

John Mulcahy

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Looks to be working well, which trace is which - REW in red? What dBFS input level do you see during the calibration?
 

Brian Steele

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Ok, so I've been a bit of an idiot. When I saw the "Calibration" option in REW, I reflexively thought it would be similar to the calibration process in the DATS software.

It Isn't.

The calibration process in the DATS software is done as follows:

1. Short the leads, run the "test lead calibration" option.
2. connect the leads across a known resistor (1 kOhm), run the "impedance calibration" option.


The REW impedance calibration process requires that the SENSE RESISTOR be shorted and the leads be left disconnected in the first step. What I did was short the leads (as that was the normal process for the DATS calibration), so obviously the resulting input during the calibration process was a lot lower than what REW would expect to see. Still, interestingly enough, the resulting graph provided exactly the same value for the impedance of the test leads as that generated by the DATS test lead calibration process.

As REW requires the sense resistor to be shorted as part of the calibration process, and as the "sense resistor" is built-in to the DATS hardware so there's no way to short it, there's basically no way to complete the REW impedance calibration process when using the DATS hardware.

Now, if there was a way to select an impedance calibration process in REW that followed the DATS software method instead... :)
 

John Mulcahy

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Somewhere in my todo list is a note to look at other calibration options for impedance measurement, though they would probably only become relevant for much higher impedances than a drive unit would present. It doesn't look like a calibration is needed in any case, the DATS input channel gains must be well matched.
 

Brian Steele

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Looks to be working well, which trace is which - REW in red? What dBFS input level do you see during the calibration?
I forgot to answer the first question. The REW measurement is in red. Measuring via REW does provide a few advantages, including longer sweep options and of course the ability to do all of the impedance and FR testing in one piece of software, so I will likely be using REW with the DATS hardware going forward.
 
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