Abstract:
An electronic keyboard instrument generates signals of frequencies respectively corresponding to keys by depressing the keys of a keyboard from a signal source, and reproduces a musical note corresponding to the generated signal. The frequency spectrum of an external signal is detected and used to control the frequency spectrum of the generated signal to cause the frequency spectrum of the generated signal to approximate that of the external signal.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to an electronic keyboard instrument, and more particularly to an electronic keyboard instrument which is adapted to make its tone approximate to a tone of an external signal. 
     Generally, an electronic keyboard instrument produces a musical note corresponding to electric signals from a speaker and has the property of obtaining various tones by freely shaping the waveform of the electrical signal. To this end, the electronic keyboard instrument is usually designed to produce sounds of tones approximate to those of musical instruments, such as a violin, a flute, an organ, a piano, a clarinet, a glockenspiel, etc. by changeover of a switch. 
     In the prior art, signals of respective scales selected by keyboard switches are applied to fixed filters for waveform shaping to obtain various tones. Accordingly, the fixed filters are each provided for each tone and selected by the player&#39;s switch changeover operation to play a tune in a desired tone. 
     SUMMARY OF THE INVENTION 
     This invention provides an electronic keyboard instrument in which an external input terminal is provided separately of such a tone changeover switch and a desired signal, for example, an audio signal of a player&#39;s voice, is applied to the external input terminal, thereby to produce a sound approximate to the tone of the signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating an embodiment of this invention; 
     FIG. 2 is a graph explanatory of the operation of the principal part of this invention; and 
     FIGS. 3 and 4 are block diagrams showing other embodiments of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, reference numeral 1 indicates a conventional electronic keyboard instrument, which comprises a signal source 2 formed, for example, with a voltage controlled oscillator group, for producing signals of frequencies of respective scales, a key switch group 3 for selectively picking up the signals of the respectively scales derived from the signal source 2, a plurality of fixed filters 4a, 4b, 4c and 4d for converting the signals from the key switch group 3 into various kinds of waveforms to provide tones of various musical instruments, a tone switch group 5 for selectively applying the outputs from the fixed filters 4a to 4d to an amplifier 6 and a speaker 7 for converting the amplified signal to a sound. 
     With the present invention, there are provided in such an electronic keyboard instrument 1 an external input terminal 8, spectrum detecting means 9 for detecting the frequency spectrum of a signal applied to the external input terminal 8 and means 10 for approximating the frequency spectrum of the signal of the electronic keyboard instrument 1 to the frequency spectrum of the external signal with the detected output from the spectrum detecting means 9. 
     In the illustrated embodiment, a microphone 11 is connected to the external terminal 8 and an audio signal picked up by the microphone 11 is amplified by amplifier 12, if necessary, and the amplified output is applied to the frequency spectrum detecting means 9. The frequency spectrum detecting means 9 can be formed for instance, with a plurality of band pass filters 13a, 13b, 13c, . . . 13n of different center frequencies, by which respective frequency components of the external signal picked up by the microphone 11 are analyzed to detect its frequency spectrum. The outputs from the band-pass filters 13a through 13n are respectively rectified by rectifiers 14a through 14n and the rectified outputs are applied to the means 10. 
     The means 10 can be composed, for example, of a plurality of band-pass filters 15a through 15n of different center frequencies for analyzing frequency components of the scale signals selected by the key switch group 3, as is the case with the spectrum detecting means 9, and a plurality of variable gain control circuits 16a through 16n for changing the levels of the analyzed output signals from the band-pass filters 15a through 15n. 
     To the variable gain control circuits 16a through 16n are respectively connected the rectified outputs from the means 9 to control the gains of the variable gain control circuits 16a through 16n in proportion to the respective analyzed frequency components of the external signal. As a consequence, the variable gain control circuits 16a through 16b provide respective frequency components of levels which are substantially approximate to the analyzed frequency components of the external signal. These outputs are added together to obtain at a terminal 17 a signal having a frequency spectrum substantially approximate to that of the external signal, which signal is applied via the amplifier 6 to the speaker 7. 
     As a result of this, the sound produced from the speaker 7 has an interval selected on the keyboard 1 and a tone nearly approximate to that of the external signal picked up by the microphone 11. Accordingly, for example, if a player depresses a key while uttering through the microphone 11, a sound which has the same interval as the depressed key and is similar to the player&#39;s voice is created from the speaker 7 of the keyboard instrument 1. Therefore, if the player simultaneously depresses a plurality of keys while singing, a sound just like a chorus is produced. 
     It is also possible to mix the rectified outputs from the rectifiers 14a through 14n by a mixer 18, apply the mixed output via a capacitor 19 to a resistor 20 and supply the resulting voltage signal at the resistor 20 to a voltage control terminal of the signal source 2, whereby to modulate, for example, the frequency of the scale signal derived from the signal source 2. With such an arrangement, when the level of an external signal suddenly changes, its differentiated output is provided at the resistor 20 and, by the differentiated signal, the frequency of the scale signal is modulated, so that the sound created from the speaker 7 can be made more approximate to the external signal. 
     The pass-band frequencies of the band-pass filters 13a and 15a, 13b and 15b, 13c and 15c, . . . 13n and 15n are respectively selected equal to each other. The center frequencies of the band-pass filters 13a and 15a, 13b and 15b, 13c and 15c, . . . are preferred to be selected, for example, 100 Hz, 150 Hz, 220 Hz . . . , as shown in FIG. 2. FIG. 2 shows the case where the external signal and the signal from the electronic keyboard instrument are frequency analyzed by thirteen band-pass filters. It is preferred to make the numbers of band-pass filters 13a through 13n and 15a through 15n as large as possible but, in practice, ten to twenty band-pass filters will suffice to make a sound of the electronic keyboard instrument 1 approximate to the sound of an external signal. 
     In the embodiment of FIG. 1, a noise source 21 is provided for superimposing, for example, a white noise, on each signal of the signal source 2. By superimposing the white noise on the scale signal, the sound from the speaker 7 is heard as if it is a natural sound. But this is not essentially related to the present invention. 
     As described above, according to this invention, a sound of the electronic keyboard instrument can be made approximate to the tone of a sound picked up by the microphone 11; for example, by applying the player&#39;s voice or a sound of another musical instrument to the microphone 11, a scale signal of a tone close to the applied external signal can be obtained. 
     FIG. 3 illustrates another example of the principal part of this invention, in which the variable gain control circuits 16a through 16n have a nonlinear characteristic to avoid distortion of a signal. To this end, at the output sides of the variable gain control circuits 16a through 16n, there are provided band-pass filters 22a through 22n, each having the same characteristic as the corresponding ones of the band-pass filters 13a through 13n and 15a through 15n provided before the variable gain control circuits 16a through 16n. With such an arrangement, distortion occurring in the variable gain control circuits 16a through 16n can be removed by the band-pass filters 22a through 22n. Where the band-pass filters 22a through 22n are respectively connected to the output sides of the variable gain control circuits 16a through 16n, the band-pass filters 15a through 15n need not always be provided. 
     FIG. 4 shows still another example of this invention, in which the external signal supplied from the external input terminal 8 is applied to a variable band-pass filter 23 to sweep its center frequency, whereby to frequency analyze the external input signal on a time divided basis. To perform this, as the center frequency of the variable band-pass filter 23 is swept, a switch 24 is changed over step by step and, in synchronism with the stepping of the switch 24, the results of the frequency analysis at respective frequency positions are temporarily stored in capacitors 25a, 25b, 25c, . . . and by the stored values, the gains of the variable gain control circuits 16a through 16n are controlled. The center frequency of the variable band-pass filter 23 is repeatedly swept by a sawtooth wave or a sine wave from a sweep signal source 26 and the switch 24 is changed over in synchronism with this sweep. Accordingly, it is sufficient that the capacitors 25a, 25b, 25c, . . . store for only one sweep period. 
     Where the storage time of the capacitors 25a, 25b, 25c, . . . can be selected sufficiently long, if the switch 24 is stopped in its step movement, as required, so that it is not connected to any contacts, immediately preceding frequency analysis results can be stored in the capacitors 25a, 25b, 25c, . . . . The system of storing the frequency analysis results in capacitors, as described above, is applicable not only to the frequency sweep system shown in FIG. 4 but also to the frequency analysis system described previously with respect to FIG. 1. 
     As has been described in the foregoing, according to the present invention, a variety of sounds unobtainable with conventional electronic keyboard instruments can easily be produced without the necessity of increasing the number of fixed filters; therefore, this invention enhances the performance effect of the electronic keyboard instrument and has great utility in practice. 
     It will be apparent that many modifications and variations may be effected without departing from the scope of novel concepts of this invention.