JPS5842476B2 - How to remove noise from musical sound waveforms - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a musical sound waveform noise removal method for removing noise on a musical sound waveform of an electronic musical instrument that performs digital processing.

Conventionally, in electronic musical instruments that perform analog processing, a method using an analog filter or the like has been adopted as a means for removing or reducing waveform distortion and noise appearing on a musical sound waveform.

However, recently developed electronic musical instruments that perform digital processing produce noise in musical waveforms that is different from that of electronic musical instruments that perform analog processing.

There is no suitable method for eliminating or reducing this that is suitable for electronic musical instruments.

FIG. 1 is a schematic diagram of a conventional digital processing electronic organ, in which 1 is a stop or tablet, 2 is a digital processing section, 3 is a D/A converter, 4 is a sound device, and 5 is a keyboard.

Information on each tablet, stop, piston, knob, etc. is provided from the stop or tablet 1, and information on the pressed state of each weight is provided from the keyboard 5 to the digital processing section 2.

The digital processing section 2 processes the musical sound waveform according to the input information and outputs it as a digital signal.

The D/A converter 3 converts the digital signal into an analog signal, and the audio device 4 outputs it as a musical tone.

In this case, the size of the emitted waveform differs depending on the type of tone selected by the tablet.

Among various tones, if the ratio of the waveform size with the minimum amplitude to the waveform size with the average amplitude is m, the number of tablets in the electronic organ is n, and the maximum number of pressed keys on the keyboard is p, then the electronic The dynamic range of the musical sound waveform of an organ is m
It becomes np times.

However, in this case, volume adjustment using expression pedals etc. is not included.

Therefore, the digital output signal from the digital processing section shown in FIG. 1 also has this dynamic range.

m, that is, the relative level ratio between each tone is at least m=3
is necessary.

Originally, p is the number of keys, but due to the simplification of the digital processing section, the number p is often limited in digital processing organs that have appeared to date, and the number p is taken into consideration based on the number of fingers on the hand, etc. = 12 is acceptable.

The number of tablets n is considered to be at least n=10 in an electronic organ.

Therefore, m''n'p=3.10.12=360, and its expression requires 9 bits in 2 reverse strokes.

Normally, this dynamic range ranges from several hundred to several thousand times.
More than 10 bits are required for reverse strokes.

Further, the number of bits required to sufficiently represent a musical sound waveform by, for example, pulse code modulation is normally 7 to 8 bits, and at least 5 bits are required.

From the above, the number of digital output bits of the digital processing section 2 is usually close to 20 bits, and at least 14 bits are required.

The digital processing section 2 is composed of logic circuits such as various registers, counters, adders, gate multipliers, etc., and the delay time increases in proportion to the number of bits due to carry of the adder and the like.

Delay time can be reduced by constructing high-speed logic elements, but for reasons such as lower power consumption, higher integration, higher reliability, and lower cost, it is necessary to construct logic circuits with the lowest possible operating frequency using low-speed logic elements. It is hoped that

Therefore, since a circuit that outputs at least 14 bits or more in parallel is constructed of low-speed logic elements, the change point of each bit may shift due to accumulation of delay time, etc., or a hazard may occur.

Then, thin Parne-like noise caused by the switching element appears in the analog signal of the D/A converter 3.

The magnitude, or energy, of this noise is determined by the product of the width and height of the thin pulse-like waveform.

The width of this noise is determined by the speed of the logic element and the number of bits, but the height of the noise is determined by the point where many bits change among each bit, and the most significant bit (MSB).
), etc., appears higher at the point where the bit changes, and is considered to be proportional to the sum of the weights of the changing bits.

The most significant change is that all bits change, and if the bit configuration is , from [bit data] x 1) to (bit data), and from (2) to (
This is the point where it changes to 1).

Generally, when an envelope is added to a musical tone signal,
The waveform has a substantially symmetrical shape in the positive and negative directions with the zero level as the center.

FIG. 2 shows one example.

Therefore, in order to use the D/A converter 3 effectively, it is necessary to
This zero level should be set approximately in the middle of the output range of the A converter.

In other words, the digital input of the D/A converter is a bit string (1)
Or in case (2), the analog output outputs zero.

The points indicated by bits 1x1) and 2) are pl, p2, .・・・・・・・・・・・・
...Position of p4 o p1 ship p3 p5 and p
2 Since p4 and pa appear at the same frequency as one cycle of the waveform, the noise has a component at the same frequency as the frequency component of the musical waveform, and the noise is always approximately within the analog output range of the D/A converter. Although the sound waveform has a fixed size, the dynamic range of the musical sound waveform is wide, so the noise appears relatively large, especially for small amplitude waveforms.

This noise is extremely audible and must be removed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a musical sound waveform noise removal method for reducing noise on a musical sound waveform of an electronic musical instrument that performs digital processing.

In order to achieve the above object, the musical waveform noise removal method of the present invention extracts only the most significant bit or the most significant bit and the next most significant bit of the musical waveform signal expressed as a digital signal, and removes those no-hits. This method is characterized in that noise is removed from a musical sound waveform by synchronizing a specific bit or all bits with a preset digital signal at the timing of a logic change.

The principle and embodiments of the present invention will be explained in detail below.

First, to explain the principle of the present invention, as described above with reference to FIG. 3, when a digital musical tone waveform is converted into an analog musical tone waveform by a D/A converter, noise appears conspicuously at point p1. p2・・・・・・・・・・・・・・・
t pa, and the highest pitch in these respects)
(MSB) was found to be changing.

In the present invention, paying attention to this, these MSB
This method detects a point and synchronizes each bit of the waveform around that point.

FIG. 4 is an explanatory diagram showing the configuration of an embodiment of the present invention, and a broken line frame 10 indicates a digital waveform shaping circuit.

In the figure, 11 is a delay circuit, 12 is a multiplexer, 13 is a storage register, and 14 is a monostable multivibrator (MM).

Only the MSB is extracted from the musical waveform information from the digital processing section, and depending on the change in this bit, H (upper) → L (lower),
The signal is input to the multiplexer 12 via a monostable multivibrator (MM) 14 that operates both from L (lower) to H (upper).

The output of the monostable multivibrator (MM) 14 is at point p1. shown in FIG. p2゜・・・・・・・・・・・・・・・
It rises at the 96th point, and its pulse width is set to cover each bit delay time of the waveform information from the digital processing section.

The storage register 13 stores binary information "1000..."
......ooo" or "Ol 11...
......111" is memorized.

The multiplexer 12 normally selects the output of the delay circuit 11, and selects and outputs the contents of the storage register 13 only during the pulse period from the monostable multivibrator (MM) 14.

In this way, monostable multipipe rake (MM) 1
Each bit is synchronized near the change point of MSH by the output of 4, and the noise can be removed.

The delay circuit 11 outputs the MSB of the signal from the digital processing section.
This delay time is provided because it is necessary to synchronize signals whose change points appear earlier than the above, and the delay time should be set to be longer than the delay time of each bit of the output of the digital processing section.

Preferably, the respective delay times of each bit are also equal.

FIG. 5 is an explanatory diagram showing the configuration of another embodiment of the present invention, in which a broken line frame 20 indicates a digital waveform shaping circuit.

In the figure, 21 is a delay circuit, 22 is a multiplexer, 23 is a storage register, and 24 and 25 are monostable multipipe lakes (MM).

Compared to FIG. 4, the delay circuit 21 has the same function as the delay circuit 11, the multiplexer 22 has the same function as the multiplexer 12, and the MMs 24 and 25 have the same function as the MM 14.

MM25 has the highest weight after the MSB) (SMSB
(abbreviated as MM24) is used as an input signal, and a pulse having a constant width is outputted at a rising point at the change point of 5M5B, similar to MM24.

The image powers of both MM24 and MM25 are entered into a storage register 23 and branched off to be applied to a multiplexer 22 via an OR gate 26.

The storage register 23 reads the corresponding amplitude value according to the signals of the MMs 24 and 25, and supplies it to the multiplexer 22.

That is, in the embodiment of FIG. 4, only the MSB is considered, whereas in the embodiment of FIG. 5, the MSB and SMSB are considered, and more of the noise can be removed.

As explained above, according to the present invention, only the MSB or the MSB and 5M5H (
Noise can be reduced from the musical sound waveform by extracting the logical sum) and using the waveform information of the change point to avoid the noisy part and synchronize and change specific bits or all bits.

The above noise can be removed to some extent by applying a deglitch type D/A converter, but this type of D/A converter
A converters are extremely expensive compared to ordinary D/A converters and are not suitable for electronic musical instruments.

In addition, this type of D/A converter requires a write pulse to be given to the built-in register, but the write pulse is set when the input waveform is a composite waveform of musical waveforms having two or more different frequencies. It was not used in electronic musical instruments because it had the disadvantage of being extremely difficult to perform.

In contrast, the present invention has a simple and inexpensive structure, and is free from the above-mentioned problems and can be said to be a musical waveform noise removal method suitable for electronic musical instruments.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a digital electronic organ, Figure 2
3 is an explanatory diagram of the principle of the present invention, FIG. 4 is an explanatory diagram showing the configuration of an embodiment of the present invention, and FIG. 5 is an explanatory diagram showing the configuration of another embodiment of the present invention. Inside, 10 and 20 are digital waveform shaping circuits, 11 and 21 are delay circuits, 12 and 22 are multiplexers, 13 and 23 are storage registers, and 14 and 24
．． 25 is a monostable multivibrator, and 26 is an OR gate.

Claims (1)

[Claims] 1 Extract only the most significant bit or the most significant bit and the next most significant bit of the musical waveform signal expressed as a digital signal, and synchronize a specific bit or all bits at the timing of the logic change of those bits. A method for removing noise from a musical sound waveform, characterized in that noise is reduced from the musical sound waveform by substituting it with a preset digital signal.