Acoustic measurements require the use of a suitable microphone, but not necessarily an expensive one.
In general we suggest that you use a microphone that is specified for test and/or measurement use. This often means a small-diaphragm condenser (or electret) microphone, and you can obtain these microphones for as little as $70.
Note that while there are some recording microphones that may appear to have suitably flat response curves for measurement, that only tells part of the story. Measurement microphones often have much lower sensitivity (allowing for higher inputs exceeding 100dBSPL) and lower self-noise characteristics.
Measurement microphones are also omnidirectional and hence are better suited to capturing reflections at all angles equally well.
Most measurement microphone manufacturers supply calibration data that FuzzMeasure can import to apply corrections to your frequency response graphs automatically, accounting for any deviations from a perfectly flat response.
Note: Measurement microphones are typically flat from DC to 1kHz, and hence are suitable for room acoustics use. Calibration data is nice to have, but not required for most room acoustics applications where relative and not absolute values are important.
FuzzMeasure cannot recognize a license key file unless it has the .fumekey3 file extension.
Some email programs will add the .xml extension, which does not allow FuzzMeasure to recognize this as a valid file to open. Other email programs will strip the extension altogether, so you have to add it.
To solve this problem, either remove the extra .xml extension, or add the .fumekey3 extension, depending on your particular situation.
The demo available at http://rodetest.com/fuzzmeasure is restricted in the following ways:
- Each document can only store two measurements
- Microphone Calibration may not be used
- New graphs may not be added to the document
- Only a limited set of document templates are available
- Documents may be saved, but data cannot be imported or exported
Should you have further questions about the FuzzMeasure demo, or if you would like to arrange an evaluation for your commerical organization, please contact us.
FuzzMeasure reports its delay based on the sample index of the peak of an impulse’s energy (which is calculated more accurately by using the Envelope Time Curve in version 3.2 and above.)
Because of the way FuzzMeasure captures its recordings, this delay is affected by the audio hardware, and the Mac’s built-in audio services.
To eliminate this delay, you can use FuzzMeasure’s Automatic Correction feature, which is located in the Audio Capture Settings window.
When checking the Automatic Correction box, you must ensure the following points are true:
There is a loopback cable hooked up between the indicated Playback and Record channels. Failure to attach this cable will result in unstable and incorrect measurements.
You are measuring with a single device selected for playback and record. Mixed device measurements are not currently advised or supported.
The Automatic Correction feature is able to work the hardware/software delays by correlating the two signals that have both passed through the audio system. The common system delay in both signals is eliminated, leaving only the signal’s transit time through the air, or the closed loop system under test.
Microphone calibration files should be in text format, and could have one of a number of file extensions (.txt, .csv, …) The extension is easy to change, but the data format is less so. Here is the start of a calibration file that I received from Earthworks:
"Transfer Function Mag - dB volts/volts (0.10 oct)(eq)(eq:aux)" "Hz" "Data" 781.25, 0.7222968 820.3125, 0.7226313 859.375, 0.7241868
The first two lines are ignored, and the file will work with just the data values. You can also add a third column that contains phase information as well.