This invention concerns a duet-sound generating method for use in an electronic musical instrument.
Generally, a duet-sound refers to an ensemble of notes. In other words, it may be a sound produced from incorporating a current melody note being played with a machine generated note or notes. To generate such a duet-sound note interval, as shown in FIG. 1, a conventional electronic musical instrument includes: a microcomputer 11 that controls related sound-source control data and generation thereof by inputting various control-switching signals and melody keyboard key switching signals; an auto-accompaniment switch 13, a duet switch 15, a filter selection switch 19, and a melody keyboard 17 that generates depressed key note signals. A sound-source generation integrated circuit (referred to as a sound-generator IC hereinafter) 21 generates related sound-source and chord sounds according to the chord and the sound-source control data from the microcomputer 11 and outputs them to the output terminals OUT1 and OUT2; a chord and bass filter 41 that, enabled under the control of the microcomputer, filters the output of the sound-generator IC's chord and bass; a rhythm generator a 43 generating rhythm signal under the microcomputer's control; a plurality of filters 45, 47 and 49 for filtering the sound-source output of the sound-generator IC 21; a pre-amplifier 51 that pre-amplifies the outputs of the filters; pre-amplifiers 53, 55 that pre-amplify the outputs of the chord and bass filter 41 and the rhythm generator 43; and a main amplifier 57 that amplifies the output of the pre-amplifiers 51, 53, 55 and outputs them to the speaker 59.
FIGS. 2a and 2b are flow chart for a conventional duet-sound generation, that is a program for use in the microcomputer 11 of FIG. 1. FIG. 2a represents the auto-accompaniment part and FIG. 2(b) is the non-auto-accompaniment. In auto-accompaniment mode's case, the duet sound is programmed to be produced when a melody note on the melody keyboard 17 of FIG. 1 is depressed and the duet switch 15 is turned `on`. The conventional duet-sound generation procedure is explained in the following section with reference to FIGS. 1 and 2. When the Filter Selection switch 19 is switched to Filter 1, e.g., a piano-voice selection signal to the microcomputer 11, the microcomputer recognizes the Filter 1 selection condition (e.g., paino sound) performs key scanning and sends a logic high signal to the output terminal S1 to enable Filter 1, filter 45. If the auto-accompaniment switch 13 becomes "on" under such a condition, the microcomputer 11 recognizes the change by key-scanning activity and determines the current mode is auto-accompaniment on. It then sends chord data for the generation of chord sounds to the sound-generator IC 21 and outputs the chord and bass-filter enable signal and rhythm-enable "high" signal at terminal S8 to enable them. During this time, the sound-generator IC 21 produces and sends the related chord sound to the output terminal OUT2, which causes the chord and bass filter 41 to output the filtered chord sound. The enabled rhythm generator 43 produces a certain rhythm. The chord and rhythm signals generated above, go through respective pre-amplifiers 53 and 55 to be amplified to a certain level, mixed in the main amplifier 57, and finally sent to speaker 59. During operation, pressing a key on the melody keyboard 17 prompts the microcomputer to check if the duet switch 15 is on. If the duet switch 15 is "off", a channel is assigned to a key to produce a sound. But, with Duet Switch 15 on, the melody keyboard 17 is scanned for a root note for the output chord. As in the logic of FIG. 2a, if a melody keyboard note is depressed without the root note present data for the root note and the melody note are allocated to two channels to be inputted to the sound-generation IC 21. At the moment, the sound-generation IC 21 generates the sound source according to the microcomputer's data and sends it to the output terminal OUT1. The sound-generation IC's sequentially outputting the data allocated to the two channels by the microcomputer 11, thereby generating the duet sound. For example, if a chord currently being outputted is a C chord, a "Do" sound that is equivalent to the root note of the chord is allocated to one of the two channels and a "Mi" sound is allocated to the other one, thereby being outputted to the sound-generator IC's output terminal OUT1. The duet sound outputted from the sound-generator IC 21 is inputted to the enabled filter 45 to be then processed into a duet sound using Filter 1 upon for the sound of the output. On the other hand, if the result of the above checking operation shows that any melody keyboard note equivalent to the root note of the outputting chord is depressed, then the outputting chord is checked to see if it is major key or a minor key. Thereafter, data for harmonious the major or minor key responding note interval with respect to the depressed key, is sent to the sound-generator IC 21. The sound-generation IC 21, at this moment, produces the sound source corresponding to the above data and sends it to the filter 1, 45 to generate the duet sound.
The duet sound produced by the instrument of FIG. 1 according to the flow chart of FIGS. 2a and b, however, provides only a mono-tone single instrument voice sound, incapable of producing duet-sounds with various instrument voices. In other words, the method may accomplish the duet sound only with a sound of a single instrument.