                 EmAv Calibration Procedure


Procedure for determining values for soundcard sensitivity parameters:

(1) Using the Options/System menu, set LS1_sensitivity=5, so that the
program will think that 1 volt (rms) generates 0.2 pascal (or 80 dB SPL)
of sound pressure.  Use the "Tone" test to tell the program to generate
an 80 dB SPL test tone on "channel A".  Measure the voltage being
delivered to "receiver A".  If this voltage is not exactly 1 volt rms,
then the DA1_sensitivity needs to be changed.  Divide the old
DA1_sensitivity by the measured voltage to obtain a new value for
DA1_sensitivity. 

(2) Likewise, set LS2_sensitivity=5, output an 80 dB SPL test tone to
"channel B", and measure the voltage being delivered to "receiver B" to
determine a new value for DA2_sensitivity. 

(3) Keep LS1_sensitivity=5, set MP_sensitivity=5, feed a 1 volt rms
signal from the first DAC into the first ADC by telling the program to
output an 80 dB tone on channel A and feeding the electrical signal from
the first DAC directly into the first ADC.  If the "RMS level" displayed
on the screen is not "80 dBSPL", then the value of the AD_sensitivity
parameter needs to be adjusted.  Take the old AD_sensivity value times
the "P-P" pressure (mPa) displayed on the screen and divide by 565.69 to
obtain a new value for AD_sensitivity. 


Procedure for determining values for probe sensitivity parameters:

(1) Set MP_sensitivity to the value appropriate for the preamp switch
setting.  Etymotic microphones are calibrated so that 1 microvolt rms
is generated by a tone at 20 micropascal rms.  If the microphone preamp
GAIN=0dB, then MP_sensitivity=0.05 (V/Pa).  If GAIN=20dB, then
MP_sensitivity=0.5.  If GAIN=40dB, then MP_sensitivity=5. 

(2) With the soundcard and microphone sensitivity parameters set to their 
proper values and the probe attached to the soundcard, place the probe 
in a "standard" acoustic cavity, tell the program to generate an 80 dB
SPL tone on channel A.  The "RMS level" displayed on the screen should
be "80 dBSPL".  If not, then adjust the LS1_sensitivity value until it
is.  One way to make this adjustment is to multiply the previous value
by the P-P pressure displayed the screen (mPa) and divide by 566. 
(Don't worry about being too accurate, the correct value varies
considerably with frequency and choice of acoustic cavity.)

(3) Repeat step 2 on channel B to adjust LS2_sensitivity. 

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