| 摘要 |
The invention concerns a music teaching instrument which involves the use of a microprocessor to control the centre frequency of a tunable bandpass filter with high Q. As a musical sound passes through this filter, only the component of the signal with this passand frequency is seen at the output. Each incoming signal has a furidamental frequency. The output of the filter with its centre frequency at the fundamental frequency of the incoming signal will have a peak value compared to those at the surrounding frequencies despite the fact that the incoming signal may be very weak in its fundamental frequency. Such a peak can be detected by sweeping the centre frequency of the bandpass filter through a range of frequencies and then reading the value of the amplitude detector connected to the output of the filter. The amplitude detector rectifies the output from the filter and then smoothens out the peaks to give an indication of the maximum amplitudes of the filter output at each frequency. The microprocessor reading the values will be able to tell the frequency at which the filter output is a maximum compared to those at surrounding frequencies. |
