JPH0683379A - Echo adding circuit - Google Patents

Abstract

PURPOSE:To provide the echo adding circuit which can generates an echo signal having a small noise component even when a companding process is performed. CONSTITUTION:This circuit is equipped with a cyclic loop which consists of a compressing conversion circuit 2 generating a logarithmically compressed signal C from a source signal A, a waveform composing circuit 1, a low-pass filter 3, a delay circuit 4, a low-pass filter 5, and an attenuator 7 and generates a delayed signal D from the signal C and an expanding conversion circuit 6 which generates the uncompressed echo signal E from the signal D. The compressing conversion circuit 2 and expanding conversion part 6 are not included in the cyclic loop, so noises which are generated there are not integrated by remaining in the loop.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an echo adding circuit, more specifically, a karaoke apparatus, a stereo set, a VTR.
The present invention relates to improvement of an echo adding circuit (a circuit for generating an echo signal from an original signal related to sound, adding the echo signal to the original signal and outputting the same) for use in audio equipment such as.

[0002]

2. Description of the Related Art Most of today's audio equipment has a so-called karaoke function for mixing and synthesizing a voice input from a microphone with another reproduction signal, etc. Functions are also essential. The echo signal for this purpose is usually generated by delaying an original signal, which is a sound such as voice or music converted into an electric signal, for a predetermined time. Further, in order to improve the reverberation effect, not only the original signal but also the echo signal is attenuated and fed back to generate a signal mixed with the original signal, and delay and mixing of this signal are repeated.

An example of a conventional configuration of such an echo adding circuit is shown in FIG. Here, 1 is a waveform synthesizing circuit, 2 is an analog logarithmic compression circuit, 3 is a low-pass filter, 4 is a delay circuit using, for example, a BBD (Bucket Brigade Device), 5 is a low-pass filter, 6 is a logarithmic expansion circuit, 7
Is an attenuator, and 8 is a waveform synthesis circuit. The original signal A input to the echo adding circuit is added with the echo signal E by the waveform synthesizing circuit 7 and is output as the acoustic signal with echo B, and finally output as sound from the speaker to the outside. , Is recorded on a tape or the like via a recording circuit.

Here, the generation of the echo signal E is basically performed by the waveform synthesizing circuit 1 by synthesizing the signal E'in which the echo signal E is attenuated to an appropriate level by the attenuator 7 and the original signal A, This is performed by delaying the combined signal by the delay circuit 4 for a fixed time to form an echo signal E. However,
From the viewpoint of, for example, reducing the cost of the delay circuit while ensuring the dynamic range, the logarithmic compression circuit 2 is placed before the delay circuit 4 and the logarithmic expansion circuit 6 is placed after it. Further, the low-pass filters 3 and 4 are also arranged before and after from the viewpoint of noise component removal and the like.

Therefore, specifically, a cyclic circuit constructed by connecting these waveform synthesis circuit 1, logarithmic compression circuit 2, low-pass filter 3, delay circuit 4, low-pass filter 5, logarithmic expansion circuit 6 and attenuator 7 in this order. The echo signal E generated from the original signal A is further attenuated and fed back by the loop. As a result, a reverberation effect is obtained in which the original signal becomes an echo signal and is attenuated and repeated.

[0006]

In such a conventional echo adding circuit, companding processing is added when the echo signal is generated. However, by performing this companding process, the effect that the dynamic range can be secured even with an inexpensive delay circuit is obtained, but on the other hand, there is the disadvantage that noise is increased by the companding circuit. Particularly, in analog companding processing, noise is likely to occur in the diode part in the logarithmic compression circuit or the logarithmic expansion circuit.

For this reason, noise cannot be sufficiently removed only by inserting a simple low-pass filter before and after. On the other hand, using a complicated and expensive filter, which has high performance, is inconvenient because the cost reduction of the delay circuit becomes meaningless. An object of the present invention is to solve such a problem of the conventional technique, and to realize an echo adding circuit having a configuration capable of generating an echo signal with a small noise component even if companding processing is performed. Is.

[0008]

The structure of the echo adding circuit of the present invention which achieves the above object is to receive an original signal relating to sound and generate an echo signal from the original signal by delaying the original signal to produce the echo for the original signal. In an echo adding circuit for outputting an acoustic signal with an echo to which a signal is added, the original signal is subjected to analog compression conversion according to a predetermined compression conversion function or further attenuated to generate a compression converted signal. A conversion circuit; a delay circuit for generating a delayed signal by delaying the received input signal or its low-pass filtered signal by a predetermined delay time, or by further low-pass filtering, An analog expansion conversion circuit for generating the echo signal by analog expansion conversion of the delayed signal according to an inverse function of the compression conversion function. When, with the added combined signal of the delayed signal or its attenuated signal and said compressed converted signal is intended to be with the input signal of the delay circuit.

[0009]

In the echo adding circuit of the present invention having such a configuration, the compression / expansion conversion circuit for performing the compression / expansion processing is removed from the cyclic loop for generating the echo signal. For this reason,
The noise generated in the compression / expansion conversion circuit will not be mixed into the echo signal, and the noise will not be mixed into the echo signal repeatedly through the cyclic loop and accumulated again, or it will be reduced. Therefore, the noise component included in the echo signal is reduced by that amount as compared with the conventional case, even without using a special noise removal circuit.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the echo adding circuit having the structure of the present invention will be described below with reference to the block diagram of FIG. Here, 1 is a waveform synthesis circuit, 2 is an analog logarithmic compression circuit, 3 is a low-pass filter, and 4 is, for example, BBD.
Delay circuit using (Bucket Brigade Device), 5
Is a low-pass filter, 6 is a logarithmic expansion circuit, 7 is an attenuator, and 8 is a waveform synthesizing circuit.

As described above, each element circuit itself is the same as the conventional one, and no special high-performance element circuit or additional circuit is used. Has been applied. That is, the first is that the order of the waveform synthesis circuit 1 and the logarithmic compression circuit 2 is reversed. Then, first, the logarithmic compression circuit 2
Produces a compressed signal C by logarithmically transforming the original signal A. Next, the waveform synthesizing circuit 1 synthesizes the compressed signal C and the feedback signal D ′ from the attenuator 7, and sends this to the delay circuit 4 via the low pass filter 3. As a result, the logarithmic compression circuit 2 is removed from the cyclic loop.

The second improvement is the feedback signal D '.
The input signal of the attenuator 7, which is the base signal of the above, is not the echo signal E which is the output of the logarithmic expansion circuit 6, but the delayed signal D which is the input of the logarithmic expansion circuit 6. As a result, the logarithmic expansion circuit 6 is also removed from the cyclic loop. Therefore, the cyclic loop for generating the echo signal is configured by connecting the low-pass filter 3, the delay circuit 4, the low-pass filter 5, the logarithmic expansion circuit 6, and the attenuator 7 in this order. By this cyclic loop, the delayed signal D generated from the compressed signal C is further attenuated and fed back. In other words, in the compressed and converted state, the reverberation effect that the original signal becomes an echo signal and is repeated while being attenuated causes the compressed signal C
Get about.

In the circuit in which the logarithmic compression circuit 2, the cyclic loop, and the logarithmic expansion circuit 6 are connected in this order, first, the signal C compressed from the original signal A by logarithmic compression conversion is generated. The delayed signal D is then generated from this compressed signal C. That is, an echo signal in a compressed state is generated. Finally, an echo signal E whose compressed state has been released is generated from the delayed signal D by logarithmic expansion conversion. As a result, an echo signal in a normal state having a reverberation effect is generated.

With such a configuration, the logarithmic compression circuit 2 and the logarithmic expansion circuit 6 as the noise source are not included in the cyclic loop in which signals are repeatedly delayed and mixed. In particular, noise generated in the logarithmic expansion circuit 6 in the subsequent stage is never fed back. Therefore, the influence of noise generated in these circuits on the echo signal E can be suppressed to a minimum. Finally, the echo signal E is added to the original signal A by the waveform synthesizing circuit 8 to form the echo-added acoustic signal B. Since feedback processing is performed in a compressed state, characteristics such as linearity of attenuation of reverberation are impaired, but overall sound quality is maintained by the original signal A even if the sound quality of the echo signal is slightly degraded. So there is no problem with sound quality.

Finally, the echo-added acoustic signal B, which is the final output from the echo adding circuit, is externally output as sound from the speaker or recorded on a tape or the like via the recording circuit. Further, FIG. 2 shows a specific configuration in which an amplifier before input of the original signal A, a switching circuit after output of the acoustic signal B with an echo, and the like are added. Here, the attenuator 7 and the waveform synthesizing circuit 1 in the block diagram of FIG.
A resistor circuit using 1 and R2 is integrally realized.

[0016]

As can be understood from the above description, in the echo adding circuit of the present invention, the compression / expansion conversion circuit for companding processing is removed from the cyclic loop for echo generation. As a result, the noise generated in these circuits does not remain in the cyclic loop and is integrated there, and the influence of noise is suppressed. Therefore, there is an effect that it is possible to generate an echo signal with a small noise component even if the companding process is performed.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an echo adding circuit having a configuration of the present invention.

FIG. 2 is a specific block diagram thereof.

FIG. 3 is a block diagram of a conventional echo adding circuit.

[Explanation of symbols]

 1 is a waveform synthesizing circuit 2 Logarithmic compression circuit 3 Low pass filter 4 Delay circuit 5 Low pass filter 6 Logarithmic expansion circuit 7 Attenuator 8 Waveform synthesizing circuit

Claims (1)

[Claims] 1. An echo adding circuit which receives an original signal related to sound, generates an echo signal from the original signal by delaying, and outputs an acoustic signal with an echo obtained by adding the echo signal to the original signal, wherein the original signal is predetermined. A compression conversion circuit that generates a compression-converted signal obtained by performing analog compression conversion according to the compression conversion function of A or by performing analog compression conversion and then attenuating, and a received input signal or a low frequency band of this input signal. A delay circuit for generating a delayed signal obtained by delaying the filtered signal by a predetermined delay time or by delaying and then low-pass filtering, and the compression conversion function for the delayed signal. An analog expansion conversion circuit for generating the echo signal by analog expansion conversion according to an inverse function of the delayed signal. Alternatively, an echo adding circuit, wherein a signal obtained by adding the attenuated signal of the delayed signal and the compression-converted signal is used as the input signal of the delay circuit.