Comparing REW, ARTA and CLIO in speaker driver and acoustic measurements - Page 3 - diyAudio
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Old 15th January 2014, 04:41 AM   #21
1audio is offline 1audio  United States
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The differences are really small. Were they both using the same mike or different microphones? The differences between the measurements could be as simple as different windowing functions. I get suspicious of too much detail in acoustic measurements, its not useful and it may be a lie. You can do very little about those tiny wiggles anyway.

Looking at REW the mike cal file is a pretty standard format but no representation of sensitivity is provided. My memory of Clio (not the latest) is that it has no provision for a mike calibration file. We have a Clio setup but no one uses it, its too klutzy for our work.
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Old 15th January 2014, 06:16 AM   #22
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The CLIO mic did not have a cal file. I can only do sensitivity cal with a calibrator. I did not cal for absolute level of both systems since I concerned more about the curve shape (resolution).

I will use my ECM8000 and UA-25 to compare both systems (CLIO + ECM8000 vs REW + UA-25 + ECM8000) again next. Use one mic in both systems.
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Old 15th January 2014, 08:08 AM   #23
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Here are data for both systems (CLIO and REW) using ECM8000 mic. One is raw data and the other is resampled and smoothed data. Resampling was used to make both data sets equal to 2048 samples.

I feel confident to use REW in all forthcoming measurements.
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File Type: jpg SPL comparison ECM8000.jpg (66.4 KB, 237 views)
File Type: jpg SPL comparison ECM8000 resample smooth.jpg (55.5 KB, 240 views)
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Old 15th January 2014, 08:22 AM   #24
Salas is online now Salas  Greece
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Solved as to why the initial differences.
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Old 15th January 2014, 12:45 PM   #25
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Comparisons of exported txt files is poor choice.

Apples v Oranges: CLIO chirp (log swept sine) of 16k v 256k sweep with REW

Rectangular window is also poor choice.


Use same length sweeps with same start and stop frequencies. Either export impulse response as wave file from CLIO and import into REW or other way around. Ensure that IR generated from REW and CLIO are aligned to same time reference. Use identical windowing to view frequency responses.

You will find differences are vanishingly small.

Sweep length determines temporal separation of HD components from linear IR. With short sweep and big FFT for frequency response, HD components get integrated into results.

Virtually all sound cards use capacitors on input to filter out phantom voltage used to power microphone. These and potentially capacitors at output of soundcard, and input of power amplifier determine HP characteristic of system. This usually approximates to 2nd or 3rd order Butterworth filter with f3 around 3-6Hz. Resolving long time constants of these filters typically require sweep length >2.7sec, i.e. 131072 sample sweep at fs 48kHz. Shorter sweeps result in aliasing artifacts in measured IR. All this is best explored with direct loopback excluding microphone and speakers.

Loopback IR measurements are important for verifying that soundcard isn't mixing input signal back into output test signal, and that operating system isn't mangling data with poor SRC, mixer functionality, or poor buffer management.

I've extensively tested REW's IR measurement capabilities, and it gets top marks. HOLM also gets top marks.

ECM8000 is generally good microphone, but needs individual calibration to get trusted results:

Click the image to open in full size.

Above is plot of 40 ECM8000 microphones from a calibration service.
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Old 22nd January 2014, 03:19 AM   #26
RNMarsh is offline RNMarsh  United States
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The rising high end will give a flat random incidence response to 10-12KHz when used far field. Good for acoustics/room EQ.
Only if measureing a speaker at close distancei will high end of speaker show rise from microphone response.

Thx-RNMarsh

Last edited by RNMarsh; 22nd January 2014 at 03:21 AM.
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Old 22nd January 2014, 03:29 AM   #27
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When I reference ECM8000 against Earthworks OM-1 I get results very similar to plots shown in above picture.

ECM8000 has crappy compensation in capsule preamp.
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Old 24th January 2014, 04:05 AM   #28
RNMarsh is offline RNMarsh  United States
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A very good microphone is the Dayton EMM-6 [+/- 1dB] and at reasonable cost.

More upscale is the APM1 mic sold thru AUDYSSEY... an 1/8th inch mic But more money.


Thx-RNMarsh

Last edited by RNMarsh; 24th January 2014 at 04:10 AM.
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Old 9th April 2014, 08:40 AM   #29
Omholt is offline Omholt  Norway
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Quote:
Originally Posted by Barleywater View Post
Loopback IR measurements are important for verifying that soundcard isn't mixing input signal back into output test signal, and that operating system isn't mangling data with poor SRC, mixer functionality, or poor buffer management.
What if you're using a USB mic? Obviously you can't run a loopback with one.
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