microphone sensor sensitivity calibration

[scanlon]

I am using a Bruel & Kjaer 4189 microphone and 2671 pre-amp and acquiring data using NI-USB 9233 DAQ device, Labview 8.0, DAQ 8.0.1 on windows 2000.

I performed mic calibration using the SVT toolkit and adjusted my DAQ sensor sensitivity in my program accordingly, to 46.2. My data acquisition was going well but bizzarly after a few days the audio suddenly started to sound exteremely sensitive. When I recalibrated I got roughly the same value as before. However when I set the sensor sensitivity to about 150, the audio sounded normal again.

I have tried this on a few different mics, new and old.

Any suggestions to what the problem might be would be much appreciated.

[Stuart_R]

With regards to the sensitivity values you have been previously using; if the sensitivity level is set fairly low it will pick up very slight variations in sound which includes noise. So you may end up amplifying a lot more noise. With a higher sensitivity level less noise would be amplified and if you want to record louder noises you will probably get a cleaner signal with a higher sensitivity setting. So even though the calibration says you can have a sensitivity of 46 you may want to keep it around 200+ just to prevent any extra noise. One other thing to double check is whether the calibration signal is being clipped which could cause inaccuracies in the data.

I would just use a value thats sounds good for you and that fits your application.