JPS62117000A - Acoustic signal generator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an acoustic signal generator.

[Prior art] Conventionally, only one specific note is digitally converted and stored in a memory such as a ROM, and by changing the cycle of the clock that reads data from the ROM, pitches are created and songs are synthesized. There is something.

[Problems to be solved by the invention] According to the above method, depending on the period of the read clock,
The cutoff frequency of the low-pass filter provided at the output must be changed. However, when a digital filter is used, if the period range of the read clock becomes wider, it becomes impossible to pass only the necessary frequencies.

This is because in a digital filter, when the cutoff frequency is fc, the frequency (3f c-5f
c), (5f c77 f c), (7fc~9fr:
) ..., so a low-pass filter is installed in the latter stage to cut off frequencies of 3fc or higher, and depending on the period of the readout clock, unnecessary frequencies may be passed through. . For example, if the frequency of the read clock is reduced to 1/4, then 3fc
is below the cutoff frequency fc of the original signal,
A low-pass filter that blocks more than 3fc of the original signal cannot block it, and it passes through.

The present invention makes it possible to reliably cut off unnecessary frequency signals even if the period of the read clock changes significantly.

[Means for Solving the Problems] The present invention provides that, when the period of the clock pulse for reading data from the storage circuit is equal to or greater than a set value, the period between the read data is changed according to the data before and after the read data. An interpolation circuit is provided to ensure that the period of data input to the digital filter is always within a certain range.

[Embodiment] In the drawings, reference numeral 1 denotes a ROM, which digitally converts and stores one specific sound. 2 is a counter for reading data, 3 is a latch circuit that latches the previous data read from the ROM, and 4 is an arithmetic circuit that is currently reading data from the latch circuit 3 and from ROM 1. The average value (X+Y)/2 of data Y is calculated. 5
is a selector which alternately selects data from the ROM 1 and data from the arithmetic circuit 4 in response to a clock input. 6 is a digital filter, 7 is a D/A conversion circuit,
8 is a low-pass filter, and 9 is a speaker. 10 is 1
/2 frequency dividing circuit, and 11 to 13 are gate circuits.

Next, the operation will be explained. Terminal F1 receives a clock pulse for reading data from ROMI, and terminal F2 receives a clock pulse for reading data from ROMI.
A clock pulse is supplied to the terminal p for the operation of the digital filter itself, and the terminal p is normally supplied with "0", and when producing a tone one octave lower, it is supplied with "1".

As will be explained in detail later, for example, to produce the sound "u", a frequency signal of this pitch is supplied to terminal F1, and to produce the sound "u", which is one octave lower, the terminal p is set to "1". west,
A signal of the same frequency as above is supplied to the terminal F1. This signal is also supplied to the digital filter 6, and processing is performed using this signal as a clock. In other words, even in the case of a sound one octave lower, the digital filter 6 processes it using the same clock, so the low-pass filter 8 can reliably block unnecessary frequencies.

Now, when the terminal p is in the state of "0", the gate circuit 12 is opened, the signal from the terminal F1 is supplied as it is to the counter 2, and data is sequentially read from the ROM 1. This data is supplied to the digital filter 6 via the selector 5, inputted by a signal from the terminal F1, and processed. The output of the digital filter 6 is converted into an analog signal by a D/A conversion circuit 7, and is supplied to a speaker 9 via a low-pass filter 8 for sound generation.

When the terminal p is 1", the gate circuit 11 is open and the terminal F
The signal from 1 is divided by 172 and supplied to counter 2, latch circuit 3, and selector 5. Therefore, ROM
1, data is read out at twice the cycle as above. This data is supplied to the selector 5 and latched by the latch circuit 3, and the data calculated by the calculation circuit 4 and R
The above data from OM 1 is selected by selector 5 and output. For example, data a, b from ROMI.

C... are read out in this order, the digital filter 6 receives data a, (a+b)/2. b.

(b+c)/2. c... are supplied in this order in synchronization with the signal from the terminal F1. Therefore, the digital filter 6 processes a signal having the same frequency as above from the terminal F1.

In this way, since a tone of a certain pitch and a tone one octave lower than this pitch are processed by the digital filter 6 using signals of the same frequency, unnecessary frequencies can be reliably blocked by using a common low-pass filter. be.

Therefore, even if the pitch of the generated music spans two octaves, unnecessary frequencies can be blocked by using a low-pass filter 8 that attenuates within one octave.

In the above embodiment, the range is up to two octaves, but it is also applicable to a larger range.

Furthermore, the output from the ROM can also be applied to methods such as ADPCM.

[Effects of the Invention] According to the present invention, unnecessary frequency signals can be blocked by a common low-pass filter over a wide range of pitches, and sound with good quality can be reproduced with a simple configuration. .

[Brief explanation of drawings]

The drawing is a logic circuit diagram showing an embodiment of the present invention. 1...ROM 3...Latch circuit 4...Arithmetic circuit 5...Selector 6...Digital filter 7...D/A conversion circuit 8...Low pass filter that's all

Claims (1)

[Claims] In an acoustic signal generating device that synthesizes a melody by digitally converting one desired note and storing it in a memory circuit, and controlling the pitch by the cycle of a clock pulse that reads data in the memory circuit, the cycle of the clock pulse is set in advance. an interpolation circuit that interpolates between the data read from the storage circuit when the value is lower than a set value according to data before and after the data; and an interpolation circuit that interpolates between the data read from the storage circuit and the data interpolated by the interpolation circuit. An acoustic signal generating device that includes a digital filter as an input, a conversion circuit that converts the output of the digital filter into an analog signal, and a low-pass filter that receives the output of the conversion circuit as an input.