The present invention relates to an electronic musical instrument and, more particularly, to an electronic musical instrument which has a large-capacity recording medium for storing waveform data and which can read out waveform data associated with a tone to be produced.
A method of producing a tone signal is conventionally known and is described, for example, in U.S. Pat. No. 4,383,462, wherein all waveform data from the beginning to the end of a musical tone signal produced by a conventional musical instrument are stored in a waveform memory and are read out at a desired rate to obtain high-quality musical tones. According to this typical conventional method, a semiconductor memory is used as the waveform memory. A waveshape memory WM31 shown in FIG. 3 of U.S. Pat. No. 4,383,462 stores a complete waveform from the beginning to the end of a musical tone signal. However, a large-capacity semiconductor memory is required to store complete waveforms for all keys, resulting in high cost. In particular, when waveform data representing a long tone is stored, the semiconductor memory becomes extremely expensive.
In order to solve this problem, in FIG. 6 of U.S. Pat. No. 4,383,462, a component of the complete waveform during an attack period is stored in a waveshape memory WM61, and another component during a fundamental period after the attack period is stored in a waveshape memory WM62. An attack waveform is read out from the waveshape memory WM61 in response to a KD signal representing a key depression timing. A fundamental period waveform is repetitively read out from the waveshape memory WM62 during a time interval after the attack waveform is completely read out (IMF signal) and until a tone end signal (DF signal) is generated. However, strictly speaking, according to this method, discontinuity arises in a connecting portion between the repetitively read out period waveforms. Therefore, the complete waveform is preferably stored in the waveshape memory.
Another example for storing the complete waveform is also described in U.S. Pat. No. 4,383,462 wherein a reading system known as a flying spot scanner is used. As shown in FIGS. 1 and 2 of this prior art, waveform data of a tone to be produced is stored in a film 12, and the waveform storage portion of the film 12 is scanned with a spot beam from a cathode-ray tube 10 at a rate corresponding to the key depression pitch. Resultant transmitted light is detected by a photo cell, and photoelectric conversion is performed.
Still another example for detecting a waveform amplitude in accordance with the amount of transmitted light is given by a system using an external large-capacity recording medium such as an optical disk, a magneto-optical disk, or a floppy disk. According to this system, a large number of waveform data can be stored at relatively low cost, resulting in convenience. In an apparatus using such a large-capacity recording medium, however, it takes a long time to trace a read head to a start point of a memory area of waveform data to be read out. Such a long access time is not suitable for an electronic musical instrument for producing musical tones in a real-time manner upon key depression (tone selection operation). For example, in floppy disks which are prevalent these days, the tracking time becomes several hundreds of miliseconds, thereby delaying production of a musical tone upon depression of a key and hence disabling real-time musical performance.
Furthermore, when waveform data becomes larger, they are stored on both sides of a floppy disk or in a plurality of sectors or tracks thereof, and in this case the access time is further delayed when data access is performed across the sectors or tracks or for the opposite side of the disk.