Author Topic: Normalize cables and iPhone response  (Read 4225 times)

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a2dconverter

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Normalize cables and iPhone response
« on: September 10, 2012, 01:34:04 PM »
I'm new here and am enjoying 'sweeping' some custom guitar efffects units and other audio gear...

I am using a Tascam iU2 as the iPhone audio interface to connect the sweep output and audio input to the device-under-test (DUT)...

Since I will always use cables and never use the microphone/ speaker, and since I am familiar with RF spectrum analyzers and Network scalar analyzers, that allow you to normalize out the test cables, I would like to to be able to 'barrel' the audio in to audio out to get a reference before testing

then I would like to normalize those cables (and the frequency response of the iPhone) out of the final response.
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This is most easily accomplished as with the HP 8568B spectrum analyzer from the '80's by the following...

1. connect the audio input and output cables together to get a resultant trace that represents the cable and test gear error.

2. save this trace to TRACE B

3. Select TRACE A and connect your device-under-test to see a resultant trace that represents the DUT's response + the cable and test gear error.

4, press the A minus B > A button (TRACE A minus TRACE B display on A)

5. this will give you only the DUT's response without any error due to iPhone response or cables.
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I can do this manually by downloading excel files of the reference and the DUT response and then just subtract them within excel and then graphing, but, it would be nice if the SignalScope PRO had a "NORMALIZE" function  :-D

Please let me know if this could be a future-feature

Regards

Joe

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Re: Normalize cables and iPhone response
« Reply #1 on: October 30, 2012, 12:12:52 PM »
Joe,

Since it sounds like your goal is to perform frequency response measurements, I would recommend that you take a look at IOScope, which is a true dual-channel analyzer. It offers frequency response magnitude and phase, group delay, coherence, impulse response and cross-correlation. With IOScope, you could solve your "normalization" concern to a great extent, by measuring the frequency response by connecting the input and output of your DUT to the two input channels on your iU2.

Still, correcting for the response of the I/O path is something that we may add to IOScope in the future (this function already exists in the Mac counterpart, which is the Dual FFT Analyzer in Electroacoustics Toolbox).

Best regards,

Ben