Example Microphone Data File
PRAXIS corrects for measured acoustic frequency responses through use of the known response and sensitivity of the microphone that is used for the measurement. PRAXIS obtains this information about the microphone by loading a microphone correction file (with file extension ".dat"). If you are using a microphone of known response and sensitivity, you can easily generate your own data file for it by use of a text editor. For many laboratory microphones, a data file that indicates a flat response (0dB at every point), and a reported sensitivity is all that is needed.
The data file for a microphone can be loaded using the "Config->Hardware Specific->Mic/Accel" menus of the main form. The files can also be used to provide the measured response of an acclerometer sensor.
The text below is an example of the format needed for a microphone calibration file. The first line needs to begin with a quote (") mark and contain the reference sensitivity value, followed by the letters MV/PA (or MV/g for an accelerometer). The line should include the characters "NINV" if the mic is non-inverting (otherwise it will be assumed to be phase inverting).
The value near 1kHz is normally specified ato be "0dB", and the reference sensitivity specifies what that 0dB equates to (in millivolts per Pascal). 1Pa rms = 94dBSPL.
Each line that does not begin with a quote is interpreted as follows:
Frequency (in Hz), response magnitude (in dB), phase angle (in degrees).
The phase angle is optional (need not be provided).
Frequencies MUST be in increasing order, but may be given at any increment. Values will be interpolated and extrapolated from those provided. Sufficient frequency points should be included to define the response shape, as Praxis will attempt to fit the points to a curve using a spline fit. The last several frequencies should be closely spaced and have the same response magnitude.
Often, the best approach to generating your own microphone data file is to
simply start with and edit an existing data file, such as the "ExampleMic.dat"
or the "flatmic.dat" file provided in the
"C:\Program Files\Praxis" directory after installation of the software or demo. You can use the Windows built-in "Notepad" application to edit this file. Here is an example of the contents of a microphone response file:
" Example Mic correction data: NINV Ref Sensitivity = 8 MV/PA "
" the number above is needed to relate the sensitivity.
" Example is for for a mostly flat mic that is -3dB at 10Hz and 50kHz
" Note the last two points are closely spaced
" Hz, dB, degrees
2.5 -12.0 0
5 -6.0 0
7 -4.0 0
10 -3.0 0
15 0 0
17 0 0
20 0 0
40 0 0
80 0 0
160 0 0
320 0 0
640 0 0
1280 0 0
2560 0 0
5120 0 0
10240 0 0
20480 0 0
40960 0 0
45000 0 0
47000 0 0
50000 -3.0 0
50001 -3.0 0