1. Field of the Invention
The present invention relates generally to an electronic musical instrument, and in particular to a polyphonic electronic musical instrument having a truncate function.
2. Prior Art
There have been proposed electronic keyboard musical instruments which have a plurality of tone generating channels for simultaneously generating tones corresponding to keys depressed on the keyboard. In such conventional musical instruments, when a key is newly depressed while all of the tone generating channels are generating tones, an assignment of the tone of the newly depressed key to the tone generating channels has been performed in one of the following methods.
One of the methods is disclosed in U.S. Pat. No. Re. 31,931 in which amplitudes of envelope waveforms for controlling levels of tones generated by respective tone generating channels are compared with each other, to detect the channel to which the envelope waveform of the smallest amplitude is applied, i.e., the channel which is generating the tone whose tone level is the lowest. Then, generation of the tone designated by the newly depressed key is assigned to the detected channel, whereby the tone corresponding to the newly depressed key begins to be generated instead of the tone which has been generated by the same tone generating channel. Another known method is disclosed in U.S. Pat. No. 4,041,826 in which counter means is provided for each of tone generating channels. And, each time a key assigned to one of the tone generating channels is released, the counter means of that channel corresponding to this released key and the counter means of those channels corresponding to keys, which have already been released, are incremented by the same value so that the contents of each counter means indicate the order of releasing of the corresponding key. When a key is newly depressed while all the channel are generating tones, the contents of all of the counter means are compared with each other to detect the counter means which contains the greatest value, whereby the tone generating channel corresponding to the earliest released key is detected. Then, the newly depressed key is assigned to the detected channel to cause it to generate a tone of the newly depressed key instead of the tone which has been generated by the same tone generating channel. A still another conventional method is shown in Japanese Patent Application Laid-Open No. 57-136698, in which envelope level data, which simulate decays of envelope waveforms of tones generated by respective tone generating channels, are compared with each other to detect the channel which is generating the tone most decayed. When a key is newly depressed on the keyboard, the newly depressed key is assigned to the detected tone generating channel to cause it to generate the tone of the newly depressed key instead of the tone which has been generated by the same tone generating channel.
Thus, with the conventional methods, when a key is newly depressed on the keyboard while all the tone generating channels are generating tones, the tone of the newly depressed key begins to be generated by the tone generating channel which has been generating the tone of the lowest tone level, the tone corresponding to the earliest released key, or the tone whose envelope level data is the smallest. When one performs a music with, for example, a piano, it is often required to perform the music in such a manner that tones in the higher tone range are produced one after another at shorter time intervals while aftersound of a tone in a lower tone range is still being produced. With the conventional methods, however, it has been impossible to achieve such a performance. More specifically, to achieve such a performance, a key corresponding to the tone in the lower tone range is first released, and then keys corresponding to the tones in the higher tone range are depressed one after another. And therefore, it is possible that the tone in the lower tone range is detected as the tone of the lowest level when one of the keys in the higher tone range is depressed. It is also possible that the envelope level data of the tone in the lower tone range becomes the smallest of all when one of the keys in the higher tone range is depressed. Further, there is a possibility that the tone in the lower tone range is detected as the tone whose key is the earliest released key. As a result, generation of the tone in the lower tone range is forcibly stopped. Such phenomena are conspicuous particularly when the decaying time of each tone is controlled in accordance with the tone pitch or tone range of the tone. Thus, with the conventional methods, it has been impossible to achieve a performance of a music equal in effect to that achieved with a piano.
As described above, with the conventional electronic musical instruments, it has been impossible to cause a specific one of tones generated respectively by all the tone generating channels to continue to be generated irrespective of the tone level or order of releasing of the corresponding key of the specific tone.