Search

In an electronic musical instrument a demultiplexing audio waveshape generator, which accepts multiplexed frequency signals and generates a complex audio waveshape. This is accomplished by having a multiplexed frequency source with one or more outputs with each output being individually connected to a weighted resistor. The outputs of the resistors are connected in common to create a current source for presentation to an analog switch. The analog switch selects the multiplexed channels to be combined to produce the audio output signal, and through the use of gating signals can be made to create pulsed waveshapes. In the preferred embodiment of the present invention the signal from the analog switch is presented to a capacitance-resistance combination. The switched current presented to the capacitor causes an incremental charging and discharging of the capacitor which corresponds to the desired contribution of that particular channel to the audio output signal. The capacitance-resistance combination also functions as a low-pass filter to smooth the waveshape and provide some formant filtering.

An electronic musical instrument is provided with a keyboard which may comprise one or more keyboard sections. Plural instrument voices are stored in memory for each section of the instrument keyboard. Each stored voice comprises a set of plural multiple bit digital words. A composite audible tone corresponding to an active key comprises varying combinations of component signals derived from the stored voices. The decay pattern of the composite audible tone is divided into successive time zones. The durations of the zones may vary. For each zone, the amplitude of at least one of the component signals of the composite tone is caused to decay while the amplitudes of the remaining component signals are either not modulated or are maintained at zero. The rate of decay of the amplitude of a component signal, hence the duration of a particular time zone, may be made a function of the keyboard section associated with the active key. In an alternative embodiment, the instrument voices are not stored in memory. Instead, plural octavely related frequency signals generated by the multiplexed accumulator of the instrument are combined to generate the signals which are to be modulated to obtain the decay pattern of the composite audible tone.

A method and apparatus for interpolating between the harmonic structures of a waveform stored in memory during the transient periods of said waveform. In an electronic musical instrument having a greater number of selectively actuable switches than generators to cause the production of sound corresponding to the respective notes of the musical scale the present invention interpolates between the harmonic structures of a waveform stored in memory during the transient period of that waveform. This is accomplished through the use of memory units having a number of locations or zones within each memory where the number of zones is equivalent to the number of discrete harmonic structures. The first of the memory units contains a discrete fixed harmonic structure in each of its zones, and a second of the memory units contains a difference value in each of its zones where the difference value is equal to the difference between the discrete fixed harmonic structure in adjacent zones of the first memory. Each of the memory units is addressed by a means for generating addresses for selectively reading out from each of the zones of each of the memories the respective values therein which are converted to an analog current and scaled to provide correlating magnitudes so that the converted and scaled voltages may be summed to form the interpolated harmonic structures of the waveform. These interpolated harmonic structures are then scaled by a waveform envelope and fed into an audio amplifier for reproducing the waveform as audible sound through a suitable sound transducing device. The different transient periods of the waveforms are detected by this scheme and cause either an attack or a decay type waveform to be generated.

The present invention is a two-part apparatus for producing note attack and decay in a conventional electronic musical instrument. Either part of the invention may be used independently of the other; however, at present the combined use is preferred. In part one, there is provided an eight state counter clocked at a rate equal to the note generator cycle and a digital magnitude comparator. The inputs (A) from the eight state counter are compared to the attack and decay scale factor inputs (B) by the comparator. The A>B,A=B functions are generated by the comparator in combination with an OR gate. The OR gate output and the sample gating signal from the conventional musical instrument are applied to an AND gate which outputs a modulated sample gating signal. In part two, the modulated sample gating signal of part one is subpulsed individually by two subpulses. Through the use of gating techniques, the most significant bit of the attack and decay scale factor is used to combine the modulated sample gating signal with the first of the two subpulses. Upon reaching the maximum pulse frequency with the first subpulse, the most significant bit of the attack and decay scale factor forces the continued maximum frequency output of the first subpulse and begins a second combination using the second of the two subpulses. The second output is combined with the first through OR gating which results in a signal with both sample period and pulse width modulation.

In a digital musical instrument, timbre modulation is effected through the use of a digital magnitude comparator and associated digital logic. Selected note frequency signals and selected scale factors are compared in the digital magnitude comparator. Selected comparator outputs are applied to the associated digital logic in conjunction with a sample gating signal. This modulation results in a segmentation of the audio waveshape in accordance with the frequency signals selected for use in the comparator. Hence, choice of lower pitched frequency signals will result in a wider segmentation period, while choice of higher pitched frequency signals will narrow the segmentation period. Timbre modulation may be employed during note attack and/or decay.

A programmable voice characteristic memory system for programming any number of different specifications in an electronic digital organ. Digital information which defines voice characteristics in an electronic digital organ is stored in a read-write specification memory. Voice characteristic information may be selectively written into the specification memory from an external data inputting device such as a punched card reader or from an external non-volatile read-write memory such as a magnetic tape. Information stored in the specification memory may be transferred to and recorded on the external non-volatile read-write memory for permanent storage and future use. Voice characteristic information stored in the specification memory may also be accessed by the digital organ to generate musical tones in conventional fashion.