HOLMImpulse: Measurements in practice - Page 15 - diyAudio
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Old 17th December 2009, 11:10 PM   #141
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Well, I went ahead and ordered a Berhinger Microphone and an M-Audio MobilePre USB - USB Powered Pre-amp and Audio Interface thingy.

Hopefully these will work with this HolmImpulse software
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Old 24th December 2009, 08:44 PM   #142
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I just installed HOLMImpulse, compared to SW it is far away better and more user friendly. I use a diy microphone with a WM61A capsule.
I measured a Cyburgs Needle with a FRS8 driver at a distance of 0.5m. I added the calibration file for the WM61 but the response is very weird. There is a steep roll off starting at 5Khz. Would you advice what causes this problem, the program says my setup is fine. Card is uncalibrated ( line out --> line in ).

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Old 26th December 2009, 10:13 PM   #143
D OB G is offline D OB G  Australia
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Can someone help me with HOLMImpulse and step response (it may already have been addressed- sorry).

I have a digital active 3-way system.

I can adjust the delay in many ways, including distance measurement, or better still, using Praxis to get the optimum step response.

But I haven't had success with HOLMImpulse.

What I have done is add delay for each driver so that the separate impulse peaks overlay the stimulus peak (zoomed in for accuracy).

Is this logic correct? It certainly measures differently this way, and doesn't sound right.

With thanks.

David
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Old 3rd January 2010, 08:15 PM   #144
Elbert is offline Elbert  Norway
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Hmm.. this is strange..

Tried to calibrate the sound-card on my lap-top using the loop-back function..
After having done the calibration sweep, the measurement is implemented, and i get a new sweep curve showing perfectly flat frequency and flat Phase response..

But when I do a new sweep (ordinary measurement this time) through the same loop, the phase is not flat anymore!

Have i missed something obvious here??

Best regards,
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Old 3rd January 2010, 08:39 PM   #145
Elbert is offline Elbert  Norway
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Here's the plot from the calibration run i attempted.. Blue is the loop-back measurement, red is the corrected response (?), and green is the measurement I did last with the loop still connected..

Don't know if anybody can read anything from this.. I was expecting the green curves to be exactly like the red ones??
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File Type: png cal loop.png (16.9 KB, 473 views)
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Old 3rd January 2010, 10:43 PM   #146
Key is offline Key  United States
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I think this happened to me and it was simply that I didn't have ADC-DAC Calibration checked in the options.
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Old 3rd January 2010, 11:32 PM   #147
Pano is offline Pano  United States
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Right! Did you see if the calibration box is checked?
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Old 4th January 2010, 06:38 PM   #148
Elbert is offline Elbert  Norway
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Well, I've only found one check-box for ADC-DAC converter, and that's the one under the device & Signal tab where you can allso initiate the calibration or import a calibration file.

When I un-tick this box and perform a new measurement, it is obvious that the measurement is not corrected with calibration.

Also, when I run the measurement, it says that calibration is being applied in that window that pops up.

What else could be wrong here??

Would really hate not to have this sorted by the time I have my measurement mic buildt!!
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Old 4th January 2010, 06:45 PM   #149
Key is offline Key  United States
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Well from the measurement I am assuming 44.1kHz. But other than that I am unsure of the signal chain. Try using ASIO. If you do not have ASIO drivers then try downloading ASIO4All.

If you use Direct Sound it could be doing an uneven resample on the fly.
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Old 4th January 2010, 07:25 PM   #150
Elbert is offline Elbert  Norway
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Well, My default was set to MME, and uppon switching to ASIO, the in and output windows went blank, hence it was obvious I missed that ASIO driver, whatever that might be!

Anyway, followed your advice, downloaded and installed, and voila; both frequency response and phase was flat as a pancake!

Seems THD went up a bit, but perhaps this is due to my set-up? I looped the headphone-output (only analog audio out available) straight in to the mic-input pulling output level allmost to the bottom to avoid digital clipping..

Perhaps the digitally limited( i assume) output gives high THD or noise and I'd be better off attenuating with some resistors?

Anyway, thanks a lot for the advice, couldn't have figured this one out my self!
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