HOLMImpulse: Measuring Frequency- & Impulse-Response

[David_Web]

"Do you want to replay the echoes in the speaker or what"
Yep that. And import it into ARTA for CSD and the like.

Any idea how to get the text file into wav in the meantime?
Audacity seems useless in importing raw regardless how it it formatted so no luck for me there.

"For me its not a big deal to convert the ASCII to whatever format I want... but for other (non-programmers) it is."
Do you have a simple comm line app that would work?
I have not been able to find one.

[askbojesen]

New Release Version 1.1.6.0 (2009-06-17)

Features/Changes:
* ASIO support
* DirectSound support
* Export Impulse response as wave file
* TimeWindow start adjusted for logsweep
* Impulse domain: No autozoom in time after measurement

http://www.holmacoustics.com/downloa.../ChangeLog.txt

Impulse to wave-file
It was quite easy to implement export to wave file, so soon we will have the other wave-file save/load utilities

MME, DS (DirectSound), ASIO
I have made a test with my USB soundcard (analog loopback)
It seems that ASIO is slightly better regarding higher order harmonic distortions. (See attachment where the THD is shown)
But MME and DS are the same.
DS is also controlled by the same volume settings, but might have improved latency, which does not matter in this application.
http://msdn.microsoft.com/en-us/library/ms790010.aspx

My measurements were reproducible, but I have no explanation why the ASIO did perform slightly better

[KSTR]

Excellent, Ask, this good news makes my day!

Thank you very much!

- Klaus

[doug20]

I have had some time to play around with this and its ease of use is impressive since I would not be able to use it if it was not easy

I believe I was able to get a good sound card calibration and my Mic calibration file imported succesfully.





Now I need to figure out how to do gated measurements on my current speakers in my HT Room.

Anyone want to step me through that? Maybe its automatic??

Thanks
Doug

[doug20]

also how do I calibrate the dB levels so I know its measuring at 75dB?

[KSTR]

Originally posted by askbojesen
I have made a test with my USB soundcard (analog loopback)
It seems that ASIO is slightly better regarding higher order harmonic distortions. (See attachment where the THD is shown)
But MME and DS are the same.
DS is also controlled by the same volume settings, but might have improved latency, which does not matter in this application.
http://msdn.microsoft.com/en-us/library/ms790010.aspx

My measurements were reproducible, but I have no explanation why the ASIO did perform slightly better

I found the same (internal semi-pro soundcard, so jitter from clock regen in the USB-card is not the cause, it seems). The error term is in the odd harmomics, 3rd especially. It's weird, isn't it?

BTW, I checked the 32bit FP .WAV export, no problems. So now I can easily convolve a step response etc. without further ado. Ya-Hoo!

- Klaus

[KSTR]

Originally posted by doug20
Now I need to figure out how to do gated measurements on my current speakers in my HT Room.

Anyone want to step me through that? Maybe its automatic?

Semi-Automatic, more or less. Zoom out, in the impulse window, and follow the info that pops up each time you move your curser from one window into another. Which tells you to simply drag the right edge of the gate window.

Or go via Options-->TimeWindow. You have to calculate the gate time into samples at first:
samples = time * sample_freq, say for 20ms: 0.02s * 44100 = 882 samples

Klaus

[doug20]

Thanks Klaus,

how do I calibrate the dB levels so I know its measuring at 75dB?

[KSTR]

Doug,

You could use a simple Radio-Shack SPL-meter nearby (as close as possible to) the mic position to check the sensivity of the mic+ADC-chain before the actual measurement, say with at 400Hz test tone. Don' use any weighting for the level-meter (or C-weighting if that is an option).

Then shift the response in the FR graph at 400Hz to that level --> scaling is then in absolute dB-SPL. Is is more robust when you use a set of frequencies (not to high, say 250, 400, and 600Hz or something). Alas, at the moment Ask has restricted the top range to 20dB, so shift to 0dB instead (will be pretty close anyway) -- not to the SPL reading --, and then just add that value to everything with your brain (or photo-chop the graph output accordingly).

Otherwise I don't know if any mic sensivity given in a calibration file is used by Ask, so we better ask Ask

- Klaus

[askbojesen]

Originally posted by doug20
how do I calibrate the dB levels so I know its measuring at 75dB?

You don't ... see:
http://www.holmacoustics.com/downloa...lse/Issues.txt
+-----------------------------------------------------------------------+
HOLMImpulse FEATURE REQUESTS
+-----------------------------------------------------------------------+
* Absolute gain (calibration dependent)

If you were to give absolute SPL then you must know:
1. The sensitivity of your soundcard
2. The sensitivity of your microphone

(Like Klaus is telling how we can get)

Future
I'll implement two options for absolute SPL.

A. Enter sensitivity for one frequency

B. Simply have absolute values in the mic-cal file

OK?