JPH0619489A - Reverberation adding device - Google Patents

Abstract

PURPOSE:To naturally cut noises without cutting a necessary sound even when a device with short word length is used for the arithmetic processing of reverberation by forcibly cutting noises left after artificial reverberation. CONSTITUTION:Digital data from a CD are inputted to comb filters 2a-2c through an input terminal 1. The data after being passed through delay circuits 4a-4c which differ in length are fed back through multiplying process circuits 5a-5c, added by adders 3a-3c, and outputted to an adding process circuit 6. At this time, a detecting process circuit 7 detects the output level of the comb filter 2a where the data is left latest with the time to detect a threshold level, thereby cutting the noises. Then the data obtained by adding the outputs of the comb filters 2a-2c by the adding process circuit 6 and the data obtained by the processing of a multiplier 12 are added by an adder 11 and outputted as digital data 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for artificially adding reverberation to a sound signal. For example, a signal from a normally recorded CD is produced as if it were produced in a large hall. The present invention relates to a reverberation adding device capable of changing the output like that.

[0002]

2. Description of the Related Art Audio equipment, such as a CD, which receives sound data, passes through a reverberation adding circuit such as a Schrader method, and outputs reverberation to the input sound, has been widely used. By changing the delay time of the comb filter and all-pass filter of the reverberation adding circuit and the multiplier when feeding back, various pseudo sound fields such as small halls and churches are created with the same circuit configuration. However, if the reverberation is long, the number of times of feedback increases, a lot of calculation error occurs, and the processed data due to the error remains after the point where the reverberation should be originally ended. You can hear it. Further, even in the countermeasure against this noise, the condition judgment for noise cutting is added after some comb filters and all-pass filters. And the signal of the sound buried in the noise is also cut at the same time.

[0003]

The conventional method has the following problems. For example, if you do not process noise, for long words,
Even after the sound is stopped and the reverberation ends, the noise will be suppressed to a level that is audible. However, when a word having a short word length is used for the arithmetic processing due to cost reduction, the shortened arithmetic error increases and the noise also increases. Also, for those that have been subjected to noise cut processing after the comb filter and all-pass filter, the noise level has already risen with the comb filter and all-pass filter, and even the necessary sound is buried in the noise, so only the noise is cut. Is difficult, and the sound is cut off the moment you cut it. An object of the present invention is to provide a method of naturally cutting noise without cutting a necessary sound even when a word having a short word length is used for reverberation calculation processing.

[0004]

According to the present invention, in a pseudo-reverberation generating circuit, even after arithmetic processing in a delay circuit having a short word length, the sound after the reverberation is not buried in the noise and the noise is naturally cut. Control means for detecting the output level of one of the comb filters of the plurality of comb filters and forcibly setting the output to 0 when the comb filter is below the threshold and operating the output data of the other comb filters. This is a reverberation adding device.

[0005]

[Function] Even if the volume of the audio amplifier or the like is increased, the annoying noise after reverberation is erased. Also, since it is unlikely that the reverberation sound will be cut off all at the same time when the noise is cut off, the sound will not sound like it is cut off in the middle, but it will sound natural.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a comb filter with a three-stage all-pass filter 1
FIG. 2 is an example of a reverberation adding circuit composed of stages, and FIG. 2 is a flowchart thereof. From the input terminal 1 to which digital data is input from a CD or the like, the comb filters 2a, 2b,
2c, and the data are input to the adders 3a, 3b, 3c after the feedback of the three-stage comb filter, and the delay circuits 4a, 4b,
After passing through 4c, it is connected as feedback to the adders 3a, 3b, 3c via the multiplication processing circuits 5a, 5b, 5c, respectively, and the outputs of the delay circuits 4a, 4b, 4c are added by the addition processing circuit 6, respectively.

At this time, the detection processing circuit 7 for detecting the output level of the comb filter 2a detects the threshold level by detecting the output level of the data remaining to the end in terms of time (having a long delay time and a large multiplication coefficient). Then, the output is cut off obliquely, and the control circuit 8 performs processing according to the flowchart shown in FIG. The adder circuits for the feedback signals of the comb filters 2b and 2c are provided with processing circuits 9b and 9c, respectively, which are controlled by the control circuit 8.

The data obtained by adding the outputs of the comb filters 2a, 2b, 2c in the addition processing circuit 6 is output through the adder 3d of the all-pass filter and the delay circuit 4d and the processing circuit controlled by the control circuit 8 through the multiplication processing circuit 5d. Feedback through 9d and addition to adder 3d, comb filter 2
The output of the comb filter 2d which forms d is added to the adder 11 via the multiplier 10, and the processing of adding the output previously processed by the addition processing circuit 6 to the output via the multiplier 12 is completed,
It becomes the digital data output 13.

Now, the processing of the processing circuit 8 will be described in detail. The output of each comb filter causes a calculation error due to feedback and the like, and data is noisy. After that, in the addition of the addition processing circuit 6, since the three outputs of the comb filters 2a, 2b, 2c are added, noise is also added at the same time, the noise level rises, and the noise passes through an all-pass filter having feedback. The noise level will rise even higher.

Therefore, the circuit of the detection processing circuit 7 of A is a circuit for forcibly cutting the noise while the noise is still small. Here, as a condition for cutting noise, a threshold level value (provisionally set to I)
Then, a counter value (tentatively J) is required for the number of times the state in which the input data (provisionally H) is smaller than the threshold level continues.

First, the output data H from the comb filter is received. (S1) Since this H exists both positive and negative, H
Takes the absolute value of. Here, the predetermined threshold I and | H | are compared. (S2) If the value of | H | is larger, the counter J
The value count for comparison with is reset to 0 and the output data H is received again. (S3) When | H | is small, if the count is less than the predetermined counter J, (S4) 1 is added to the count and the output data H is received again. (S5) If the counter J and the count are equal, the output after this circuit is forcibly set to 0 (S6).

Otherwise, the data H output from the comb filter before this circuit is output. Also, at the same time when it is forcibly set to 0, the output of point B, the output of point C, and D
The point output is also forced to 0. For example, if the word length is 16 bits, the point B, the point C, and the point D are provided with the value X, and are ANDed with the values after the multiplication processing circuits 5b, 5c, and 5d. The value of X can be easily realized by setting X = 0 only when it is forcibly set to 0 at the point A, and setting X = FFFF in hexadecimal otherwise. By doing so, the outputs of the points A, B, C, and D become 0, and by repeating this, the output 13 becomes 0, and a silent state is obtained.

[0013]

As described above, according to the present invention, when a word having a short word length is used as an arithmetic processor, the noise is forcibly cut before the noise becomes large.
Noise can be cut without cutting the required sound together. Also, when the volume of the amplifier etc. is raised,
No offensive noise is generated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart thereof.

[Explanation of symbols]

 1 input terminal 2a, b, c, d comb filter 3a, b, c, d, 11 adder 4a, b, c, d delay circuit 5a, b, c, d multiplication processing circuit 6 addition processing circuit 7 detection processing circuit 8 control circuit 9b, c, d processing circuit 10, 12 multiplier 13 output terminal

Claims (2)

[Claims] 1. An adder circuit for a plurality of comb filters, level detecting means for detecting an output level of one of the comb filters, and compulsory when the level detected by the level detecting means is below a threshold. A reverberation adding device characterized in that the output data is set to 0 and a control means for operating the output data of another comb filter is provided, and noise remaining after the pseudo reverberation is forcibly cut. 2. The comb filter has an adder at its input, and the output from the delay circuit is added to the input data by the adder via the multiplication processing circuit, and the output of the multiplication processing circuit is controlled by the control means. The reverberation applying apparatus according to claim 1, wherein.