JPS6240716B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waveform synthesis circuit, and particularly to a novel improvement for obtaining a waveform with an arbitrarily set amplitude.

In this type of waveform synthesis circuit that has been used in the past, when the intensity of each overtone spectrum increases by N times, the amplitude of the synthesized waveform also increases by N times.
Since the number of displacement bits of the waveform data is fixed, as each overtone spectrum becomes larger and the amplitude of the synthesized waveform becomes larger, an overflow from the fixed number of bits will occur, and the synthesized waveform that should originally be created will be distorted. The drawback was that it was not available.

The present invention aims to provide an extremely effective means for quickly eliminating the above-mentioned drawbacks, and includes an amplitude level switch, which allows the amplitude of the waveform to be synthesized to be set. The present invention relates to the configuration of a waveform synthesis circuit which is characterized in that it converts a spectrum from a fundamental wave to a suitable harmonic into a waveform having a set amplitude without causing overflow.

Hereinafter, this invention will be explained in detail with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention, in which numeral 1 is an amplitude level switch that sets the amplitude of the waveform to be synthesized, numeral 2 is an order switching switch that switches the order of overtones, and numeral 3 is an order switching switch 2. This is a harmonic level switch that sets the spectral intensity of the harmonic of the selected order.

4 is an overtone level register in which the spectral intensity of each overtone set by the order changeover switch 2 and overtone level switch 3 is set; 5 is an inverse FFT circuit that synthesizes a waveform from the data of overtone level register 4; 6 is an inverse FFT This is a temporary waveform data register that temporarily stores one cycle of the waveform synthesized by the circuit 5.

7 is a comparator for detecting the maximum amplitude in the temporary waveform data register 6; 8 is a register for storing the amplitude level set by the amplitude level switch 1; 9 is a register for storing the set amplitude level b and the composite waveform. This is a multiplier that calculates the ratio between the maximum amplitude a and the maximum amplitude a.

10 is a multiplier that multiplies the data C in the temporary waveform data register 6 by the ratio d determined by the divider 9;
12 is envelope data; 13 is a multiplier that multiplies the waveform data e from the waveform data register and the output from envelope data 12; 14 is the result of multiplier 13; 15 is a harmonic level register 4 for producing sound according to the D/A converter.
Alternatively, a display changeover switch 16 selectively displays the contents of the waveform data register 11, and 16 is a display device that displays the contents of the overtone level register or the waveform data register according to the display changeover switch 15.

In electronic musical instruments, the waveform data register 11
One cycle of waveform data e stored in the envelope data 12 is repeatedly read out and combined with the output from the envelope data 12 to create sound. Generally, instead of the waveform data register 11, a ROM or the like is used that stores waveform data for one period.
Even when using ROM, the waveform data register 11
Even when using , the number of bits in the waveform displacement direction is fixed. Even when the spectrum from the fundamental wave to higher-order overtones is synthesized, the amplitude of the waveform must be kept within a range that can be expressed by the number of bits in the displacement direction.

As shown in FIG. 5, the overtone level register 4 has an address corresponding to the harmonic order set by the order changeover switch, and an integer 5 bit of data is each overtone spectrum of the integer 5 bit set by the overtone level switch 3. Corresponds to intensity.

As shown in Fig. 6, from the fundamental tone to the 31st overtone can be set using the order changeover switch 2 and the overtone level switch 3, and from the 32nd to the 63rd overtone.
The zero overtone (DC component) has a spectral intensity of zero.

The inverse FFT circuit 5 is connected to the 31 of the overtone level register 4.
It is possible to synthesize the overtone spectrum up to overtones. If the spectral intensity of the fundamental wave is the maximum 5-bit integer, 31, and the spectral intensity of the other overtones is zero, the amplitude is a digitized sine wave (or cosine wave) with an integer of 31, as shown in Figure 2. becomes. In this case, the waveform data requires a code bit and 5 bits of an integer. 64 for one cycle of this waveform data
The point is set in the temporary waveform data register 6. If the spectral intensity of the second overtone is 31 and the others are zero, the result will be as shown in Figure 3. If the spectral intensities of the fundamental tone and second harmonic are 31 and the others are zero, the result will be as shown in Figure 4. The spectral intensity of each overtone is
If all are 31 and the peaks match (in the case of Cosin), the result of inverse FFT5 requires a 10-bit integer and a sign bit. Therefore, the temporary waveform data register becomes as shown in FIG. One cycle of 64 addresses consists of a code bit and 10 bits of integer data. A comparator 7 selects the maximum value (amplitude) of one period of the waveform stored in the temporary waveform data register 6, and outputs the maximum value as a.

On the other hand, the waveform data e to be multiplied by the output of the envelope data 12 and the multiplier 13 is a 64-point integer stored in the waveform data register 11.
This is data for one period of 5 bit code and 1 bit. The data in the waveform data register 11 consists of a sign bit and a 5-bit integer.
You can get a maximum of +31 and a minimum of -31.
The amplitude level switch 1 and the amplitude level register 8 determine the amplitude of the waveform data within this range. A 5-bit integer is input from the amplitude level switch 1 and set in the amplitude level register 8. For example, when 5-bit integer data 25 is input from the amplitude level switch 1, the maximum value (amplitude) of the waveform data register 11 becomes 25. From the amplitude level register 8, the integer 5-bit data b is sent to the comparator 7.
From then on, the maximum value data a in the temporary waveform data register 6 is input to the divider 9 in the form of a 10-bit integer part. The divider 9 outputs b/a as 15-bit fixed-point data d. d is integer part 5 bit, decimal part
Represented in 10 bits.

Sign of 64 points of temporary waveform data register 6
bit and integer 10 bit data are multiplied by the 15 bit output data of divider 9 and multiplier 10, and the integer part 5 bit
is stored in the waveform data register 11 as 1-bit waveform data. A code bit and a 5-bit integer waveform data e are repeatedly read out from the waveform data register 11 and multiplied by the output of the simultaneous envelope data 12 in a multiplier 13 . Thereafter, the signal is passed through the D/A converter 14 and output as sound from the speaker 17. Either the spectrum information stored in the overtone level register 4 or the waveform information stored in the waveform data register 11 is selected by the display changeover switch 15 and displayed on the display 16.

As described above, amplitude level switch 1, amplitude level register 8, comparator 7, divider 9, multiplier 1
By using 0, 11 bit depending on the overtone composition
Each data in the temporary waveform data register 6 that requires
It can be converted to fit in . Since the amplitude level switch 1 cannot take a 5-bit integer with a maximum of 31 or more, the contents of the waveform data register will not overflow. In addition, by setting the amplitude level switch 1 to an arbitrary integer between 0 and 31, the amplitude of the waveform data stored in the waveform data register can be given with 5-bit accuracy, making it possible to change the tone of an electronic instrument. The waveform data can be adjusted to a predetermined amplitude while freely manipulating the overtone spectrum, which is extremely effective in creating the tone of an electronic musical instrument.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an embodiment of the present invention, and Figure 2 is a waveform when the fundamental wave level is set to 31. Figure 3 shows the waveform when the level of the second harmonic wave is set to 31, Figure 4 shows the waveform when the level of both the fundamental wave and the second harmonic wave is set to 31, and Figures 5 and 6 are logic tables. . 1... Amplitude level switch, 2... Order selection switch, 3... Harmonic level switch, 4... Harmonic level register, 5... Inverse FFT circuit, 6... Temporary waveform data register, 7... Comparator, 8 ... Amplitude level register, 9 ... Divider, 10 ... Multiplier, 11 ... Waveform data register, 12 ... Envelope data, 13 ... Multiplier, 14 ... D/
A converter, 15... Display changeover switch, 16...
Display unit, 17...Speaker.

Claims (1)

[Claims] 1. An order selection switch that switches to multiple harmonic orders, a level switch that sets the waveform amplitude of the frequency selected by this order selection switch,
Inverse FFT (fast Fourier exchange) that synthesizes and outputs multiple waveform data set from the order switching switch and level switch, and this inverse FFT
an amplitude level switch for inputting a desired waveform amplitude; and a divider for calculating the ratio between the output of the amplitude level switch and the maximum output of the temporary waveform register. , a multiplier that multiplies the output of this divider by the output of the temporary waveform register, and a waveform data register that inputs the output of this multiplier, and adjusts the output of the waveform data register based on the setting input of the amplitude level switch. A waveform synthesis circuit characterized by preventing overflow.