JPH043556B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a waveform generator for an electronic musical instrument, and more particularly to a method for storing waveform data in a waveform memory in a compressed representation format to reduce storage capacity and simplify subsequent waveform calculations. BACKGROUND ART Conventionally, in waveform storage devices for electronic musical instruments, waveform data values have been stored as they are in a linear or logarithmic representation format. As a result, the number of data bits has increased, and the storage capacity has tended to increase. In particular, data of the entire waveform or multiple cycles of the waveform from the start to the end of the musical tone is stored in the memory,
If you try to obtain a high-quality musical waveform signal equivalent to a natural instrument sound by reading this, if the waveform data for one sample point is multi-bit, the overall memory capacity will become enormous. There is a risk. If the number of bits per piece of data is reduced in order to avoid this problem, the dynamic range will become narrower, causing a loss in sound quality. Also, if the waveform data is multi-bit,
The arithmetic circuit for level control has also become larger, and
Digital-to-analog converters have also become larger and more expensive. OBJECT OF THE INVENTION The object of the present invention is to eliminate the above-mentioned drawbacks by making it possible to process digital waveform data in a data representation format that can provide sufficient dynamic range with a small number of bits. The present invention aims to provide a waveform generator for an electronic musical instrument that can reliably generate a desired waveform. Summary of the Invention The present invention is characterized in that, for each sample point of a desired waveform, the difference data of amplitude values between adjacent sample points is expressed as a floating point representation consisting of a mantissa and an exponent, and this is stored in the waveform memory. It's on the point I remember. Then, by using a floating digital-to-analog converter to convert the mantissa data corresponding to the read output of the waveform memory into analog at a ratio according to the exponent data, the real value of the difference data for each sample point is converted into an analog signal. demand. By cumulatively adding and subtracting the analog signal of the difference data thus obtained using an analog accumulator, an analog amplitude value for each sample point is obtained. By storing the difference data rather than the waveform amplitude value itself, the number of data bits per sample point can be reduced, and by representing the difference data in floating point representation, the number of data bits can be further reduced. can. Further, when weighting calculation is performed on data read from the waveform memory, a floating point type calculation circuit can be used, so the configuration of the calculation circuit can be simplified. Further, since cumulative addition and subtraction are performed after converting floating point type difference data into real-value analog signals, a simple-configured analog accumulator can be used as an arithmetic circuit for this purpose. Embodiment In FIG. 1, the waveform memory 10 stores, for example, the difference in amplitude value between adjacent sample points for each sample point of a musical sound waveform consisting of multiple cycles from the start to the end of sound as shown in FIG. Data expressed in floating point representation is stored. An enlarged example of the waveform sample point amplitude value is shown in Figure 3, where sample points 0, 1,
The amplitude values of 2, 3, 4... are A ₀ , A ₁ , A ₂ , A ₃ , A ₄
..., the difference data of sample points 1, 2, 3, 4... Δa ₁ , Δa ₂ , Δa ₃ , Δa ₄ ... Δa ₁ =A ₁ −A ₀ , Δa ₂ =A ₂ −A ₁ respectively , Δa ₃ =A ₃ −A ₂ , Δa ₄ =A ₄ −A ₃ ,... The waveform memory 10 decomposes the digital values ⁽ representatively represented by _{Δa i} ) of the difference data Δa ₁ , Δa ₂ . The data of the mantissa part M and the data of the exponent part E are stored. B is the base number, and in binary system it is generally B
=2. An example of the storage format of the waveform memory 10 is shown in FIG. 4, in which the data M p to M o of the mantissa part M of the difference data Δa _i determined for each sample point as described above and the data M _p to M _o of the exponent part E are Data E _p to E _o are stored corresponding to each sample point address O to N, respectively. A keyboard 11 is used as a means for specifying the pitch of a musical tone to be generated, and information (key code KC) indicating the key pressed on the keyboard 11 is given to an address data generator 12. The address data generator 12 is a means for reading waveform data from the waveform memory 10 in accordance with the pitch specified on the keyboard 11, and reads sample point address data that sequentially changes at a rate corresponding to the specified pitch. Occur. The sample point address data generated from this address data generator 12 is stored in the waveform memory 10.
The mantissa data M _p to M _o and the exponent data E _p to _{E o} corresponding to each sample point address O to N stored therein are sequentially read out. Note that the address data generator 12 is connected to the keyboard 1.
1, it is reset to the initial address (ie, sample point address O) by a key-on pulse KONP that is generated instantaneously when a certain key is pressed. This address data generator 12
Since any known technique can be used as the address data generation technique in , the details thereof will not be particularly shown. The mantissa data M and the exponent data E read from the waveform memory 10 are sent to a multiplier 13 for level control.
and are input to the adder 14, respectively. The key scaling or touch function generator 15 converts the level coefficient data for key scaling into the key code of the pressed key.
The level coefficient data for touch response control is generated according to a predetermined key scaling function using KC as a parameter, or the level coefficient data for touch response control is generated according to a predetermined touch function using touch detection data as a parameter. K=m・2 ^e (where K is the level coefficient) Mantissa data m expressed in floating decimal point notation
and exponent part data e. The multiplier 13 multiplies the mantissa data M and m, and the adder 14 adds the exponent data E and e, resulting in "K.
A weighting operation at the floating point level equivalent to the weighting operation at the real number level called Δa _i is performed. That is, K・Δa _i = m・2 ^e・M・2 ^E = (m・M)・(2 ^e+E )
The first term (m·M) on the rightmost side is multiplied by the multiplier 13, and the exponent part of the second term (2 ^e+E ) is added by the adder 14. By the way, when we look at the sequence of mantissa data M, as shown in Table 1, the values range from the maximum value 1111... (all "1") to the minimum value, corresponding to each value of the exponent data E.
Continuity is shown up to 0000... (all "0"), but discontinuity exists between values of exponent data E that are different. In other words, when the exponent data E is "0", the mantissa data M directly corresponds to a real number, but when the exponent data E is other than "0", the mantissa data M does not directly correspond to a real number. Instead, as shown in the right column of Table 1, the value obtained by adding "1" to the high-order bit of the mantissa data M corresponds to the real number, and by doing this, the value of the exponent data E differs. The continuity of the sequence of mantissa data M between objects is ensured.

【table】

Claims (1)

[Scope of Claims] 1. A waveform memory that stores in advance the difference data of amplitude values between adjacent sample points for each sample point of a desired waveform, each representing the data in a floating point representation consisting of a mantissa part and an exponent part; A floating digital-to-analog converter converts the mantissa data corresponding to the read output of the waveform memory into analog at a ratio according to the exponent data, and the amplitude of each sample point is calculated by cumulatively adding and subtracting the analog-converted signals. A waveform generator for an electronic musical instrument, comprising an analog accumulator for obtaining an analog signal corresponding to a value. 2. The mantissa data and exponent data corresponding to the read output of the waveform memory to be converted by the floating digital-to-analog converter are data obtained by appropriately weighting the mantissa data and exponent data read from the waveform memory. A waveform generator for an electronic musical instrument according to claim 1. 3. The weighting coefficient is expressed in a floating point representation consisting of a mantissa part and an exponent part, and the weighting is performed by multiplying the mantissa part data together and adding the exponent part data together. A waveform generator for an electronic musical instrument according to claim 2. 4. The waveform generator for an electronic musical instrument according to claim 1, wherein the desired waveform is a musical sound waveform. 5. The waveform generator for an electronic musical instrument according to claim 1, wherein the desired waveform is an envelope waveform.