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For the measurement of aircraft noise or car engine noise, we use the digital video camera with external stereo microphones. Sound is recorded by16bit/44kHz sampling with motion pictures. Then, the audio data is imported to the computer and analyzed by the RA (Realtime Analyzer). I introduce here examples of the equipment that is reasonably available. Those who would try to the similar measurement can use them.
|Digital handycum and notebook PC (Sony vaio) is connected
by iLINK cable. The vaio software Dvgate can control the video deck.
Set the input device of the Realtime Analyzer as "wave" to get the internal signal in the computer. Replay the recorded movie and start the ACF measurement.
The input sound level is simply adjusted by the sound level meter's value. For the precise measurement of the sound pressure level, you should calibrate the microphone before the measurement. See RA's operation guide for how to calibrate the microphone.
Video camera is very convenient to record the situation of the measurement.
For the sound measurement, it is important to use a proper microphone and amplifier. Preparation of the equipments and the software is also important. It may seem difficult for untrained users, but don't worry. Our measurement software, DSSF3, is equipped with a number of support functions for performing the correct measurement easily. Anyone can measure sound correctly by following the procedure written in the operation guide of the program manual.
I usually use recording equipments such as MD and DAT recorder with automatic recording mode. When I need a picture, I use Sony digital video camera which is equipped with the 16-bit 48 kHz sampling stereo sound recorder. I pay a special attention to the recording level, because the quality of the measurement is decided by the dynamic ranges of the microphone and the microphone amplifier.
The quality of the equipments (especially the microphone) greatly affects the measurement results. If available, you should use the highest-class microphone. But such microphones are very expensive. Comparatively cheap and excellent microphones are also available.
See also Additional devices for sound measurement for more information.
Element: Stereo etectret condenser
Price: JPY 7,800
The audio capability is important. If it does not allow 16 bits recording, the dynamic range is insufficient and it can not be recommended for the sound measurement. The products listed below satisfy this specification.
PCM digital stereo recording 12bit 32kHz / 16bit 48kHz
PCM digital stereo play 12bit mode / 16bit mode
Speech mode should be set at 16bit.
We usually use SONY VAIO and DELL INSPIRON, but of course you can use other PC if it can control the video camera.
April 2003 by Masatsugu Sakurai