| 摘要 |
PURPOSE:To turn the directivity into an acute angle and also to secure the equal directivity to the frequency by selecting the amplitude frequency characteristic of a two-dimensional filter and the proper sampling frequency that satisfy the specific conditions. CONSTITUTION:The microphones units 1-4 which are linearly arrayed with the spaces (d) secured among them convert the sound waves into the electric signals. The A/D converter means 11-14 converts the electric signals into the digital values which are inputted to a two-dimensional filter 15. The output of the filter 15 is converted into the analog value by a D/A converter means 16. The frequency characteristic of the means 16 is corrected and flattened by a frequency characteristic correction means. Then the amplitude frequency characteristic of the filter 15 is corrected so that a passing area is secured in a linear area which is shown by an equation I on a two-dimensional frequency plane expressed by the normalized time frequency f1 (-0.5<=f1<=0.5) and the normalized space frequency f2 (-0.5<=f2<=0.5) and also that the time sampling frequency fs of the filter 15 is kept in the range of an equation II respectively. |
