JP2901240B2 - Reverb generator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverb generator, and more particularly to a reverb generator having a transfer function having a dispersion characteristic in a feedback path. 2. Description of the Related Art Conventionally, a reverb generator is used in an audio device such as an electric musical instrument or a sound reproducing device to process an output audio signal to change a sound effect or increase a sense of reality. . A conventional reverb generator includes a delay circuit that adds a fixed time delay to an input signal regardless of frequency and outputs the delayed signal, and adds a predetermined amount of attenuation to an output signal of the delay circuit regardless of frequency to output the delay signal. It consists of an attenuator that returns to the input side. In such a conventional reverb generator, a tape recorder or the like has been used as a delay unit before, but recently, a digital circuit device is often used. In a typical conventional reverb generator, a series of impulses that exponentially attenuate according to the attenuation constant of an attenuator that defines a feedback amount for one input impulse is repeated with a delay time defined by a delay circuit. In the reverb generator having such a response characteristic, the variable parameters are limited to two, that is, the attenuation constant of the attenuator and the delay time of the delay circuit, so that the degree of freedom in processing the output audio signal of the audio device is limited. I will. Also, if you want to use such a reverb generator for electric musical instruments and sound reproduction devices to obtain the reverberation effect and realism of a concert hall,
If the attenuation constant is reduced or the delay time is increased, a very unnatural feeling is generated, and in an extreme case, it is possible to hear that several sounds radiated from the loudspeaker overlap. For this reason, the selection range of the attenuation constant and the delay time is limited to an extremely narrow range unless intentionally aiming for such a special effect. The resulting sound effect is also limited. For example, when the delay time is typically about 30 milliseconds or more, the unnatural feeling becomes so severe that it cannot be used. Also, if the amount of return is increased and reverb is applied too much, it becomes unnatural. On the other hand, according to Japanese Patent Application No. 60-123630 filed by the same applicant as the present application, the input stereo audio signal is reproduced as it is from ordinary left and right speakers, and at the same time, the time delay depending on the frequency is reduced by using a phase shifter in the low band. There is known a device that simulates the acoustic space of a concert hall by reproducing the delayed stereo sound signal from respective speakers in addition to increasing the amount of delay in the high frequency range. Furthermore, a device for simulating the effect of indirect sound due to multiple reflections generated in a concert hall by cascading a phase shifter giving this frequency-dependent time delay to a conventional reverb generator is disclosed by the same applicant as the present application. This is described in Japanese Patent Application “Stereo Audio Signal Reproducing Apparatus” filed on March 4, 1987. Each of the above devices can simulate the acoustic space in a concert hall by using a phase shifter having a frequency-dependent delay characteristic, but when used as a reverb generator, it lacks a return path. However, there is a problem that the reverberation effect that can be generated is limited because the phase shifter is not included inside the return path. Means for solving the problems The present invention is directed to a delay circuit means for adding the above problem to an input audio signal input to an input terminal, adding a fixed time delay irrespective of frequency, and outputting from an output terminal, and the delay circuit An attenuator means for attenuating an output signal output from an output side of the means in accordance with a predetermined attenuation constant and feeding back to the input side of the delay circuit means, wherein A signal path passing through the output terminal to the output terminal in series with the delay circuit means and in a return path from the output side of the delay circuit means to the input side of the delay circuit means through the attenuator means. Where Here, n is an integer of 2 or more, τi is a time constant, and s is a reverb generator characterized by comprising a phase shift means having a transfer function represented by a Laplace operator. The phase shift means shifts the phase of the input audio signal in accordance with a frequency-phase lag curve that sharply rises with frequency in the low frequency band and gradually flattens in the high frequency band. This results in a smaller time delay, or variance. Since the phase shift means is included in series with the delay circuit means and in the return path passing through the attenuator, the incoming audio signal is output after being repeatedly dispersed, and a very natural reverberation effect occurs in the output sound. . Further, in such a reverb generator, since the delay characteristics of the phase shifter are variable, the number of parameters that can be adjusted is increased as compared with the conventional reverb generator, and there is an advantage that the degree of freedom in adjusting the acoustic effect is increased. Embodiment FIG. 1 is a block diagram showing an embodiment of a reverb generator according to the present invention. The input audio signal input to the input terminal 1 of the reverb generator 10 is delayed for a fixed time irrespective of the frequency by a delay circuit 2 and then phase-shifted by a phase shifter 3 having a transfer function g (s) depending on the frequency. Is output to the output terminal 4 as an output audio signal. Transfer function g
(S) is the following equation Here, n is an integer of 2 or more, τi is a time constant, and s is defined by a Laplace operator. Add. In response to this phase shift action, the output signal of the phase shifter has a time delay that is large in the low band and small in the high band. Further, the output audio signal is branched at the connection point 5 and fed back to the input side addition connection point 7 of the delay circuit 2 through the attenuator 6. Hereinafter, the term “feedback path” is used to refer to a signal path from the output side of the delay circuit 2 to the input side of the delay circuit 2 via the connection point 5, the attenuator 6, and the addition connection point 7. Accordingly, the reverb circuit of FIG. 1 includes the phase shifter 5 in the feedback path 8. Further, the order of the delay circuit 2 and the phase shifter 3 may be reversed. FIG. 2 is a block diagram equivalent to the block diagram of FIG. The transfer function e− ^{S · ΔT in} FIG.
K represents the transfer function of the attenuator 6. g (s) is a transfer function of the phase shifter 3 defined by the equation (1). Here, ΔT is a delay time generated by the delay circuit 2 and is an amount independent of the frequency. K is a positive constant smaller than 1 corresponding to the attenuation constant of the attenuator. Using these transfer functions, the transfer function G (s) between the input terminal 1 and the output terminal 4 in FIG. Is represented by When the expression (2) is expanded, the following expression is obtained. G (s) = e− ^{s · ΔT} · g (s) [1 + K · e
^{−s · ΔT} · g (s) + K ² · e ^{−2S · ΔT} · g ² (s) +
^{K 3 · e -3S · ΔT ·} g 3 (s) + ... ] will be briefly described below the transfer function g (s). For simplicity, if n in equation (1) is 1, g (s) is Is represented by The gain and phase shift of the phase shifter having the transfer function represented by the equation (4) are shown as functions of frequency in the Bode diagram of FIG. However, the frequency on the horizontal axis is shown on a linear scale. As can be seen from FIG. 3, in the element having the transfer function of the equation (4), the gain is independent of the frequency, but the phase rises (delays) in the negative direction together with the frequency in the low frequency range and −180 in the high frequency range. It has the property of asymptotic to °. Also, it can be seen that the frequency fi at the point where the phase delay becomes 90 ° is defined by the equation fi = 1 / 2πτi (5). When n in the expression (1) is an arbitrary integer other than 1, the gain is 1 as in FIG. 3 and does not change with respect to the frequency, but the change in the phase is n times. The amount of change in the phase is asymptotic to n × (−180 °). FIG. 4 schematically shows the amount of phase change when n is large. Thus, when n is large, it can be seen that the phase lag of the element having the transfer function given by equation (1) has a characteristic that it sharply rises with frequency in a low frequency region and becomes flat in a high frequency region. By the way, when the phase is φ, the delay time at each frequency f is dφ / d
Since it is proportional to f, when n of g (s) is large, there is a tendency that the lower the frequency, the larger the frequency corresponding to the phase delay that rises sharply with frequency in the low frequency range. FIG. 5 shows a typical example of an impulse response of a phase shifter having such a frequency versus phase delay or time delay characteristic. As can be seen from FIG. 5, a high frequency component appears in the output immediately after the impulse is input, and a low frequency component appears with a delay. This is dispersion. The phase shift circuit having the transfer function represented by the equation (1) can be constituted by a large number of cascaded operational amplifiers. The specific circuit structure is described in Japanese Patent Application No. 60-123630 by the present applicant. Therefore, the description is omitted in the present application. Returning to the transfer function G (s) represented by the equation (3), G
Examining the convergence of (s), the absolute values of e− ^{S · ΔT} and g (s) are 1, and since K is a positive number smaller than 1, each expansion term of G (s) becomes smaller with n. It can be seen that they converge. That is, the output terminal 4 of the reverb generator 10
, A response that becomes smaller each time it is repeated at time ΔT is superimposed and appears. FIG. 6 shows the transfer function G (s),
That is, the impulse response of the reverb generator 10 according to the present invention is shown for each expansion term. In FIG. 6, (a) is the input impulse, and (b) is the first term e in equation (3).
^{The response} delayed by ΔT by ^−SΔT · g (s) and the variance is added, and (c) is the second term Ke ^{−2S · ΔT} · g ²
The response delayed by 2ΔT by (s) and further added with variance is shown in (d), and the response in (d) is the third term K ² e− ^{3S · ΔT} · g.
³ (s) represents a response delayed by 3ΔT and further dispersed. In addition to the illustration, a response sequence converging with an infinite number of n is formed according to each term of the expansion of the equation (3). Since the transfer function G (s) includes g (s) in the form of a power series, the amount of phase change caused by g (s), that is, the magnitude of dispersion, increases in proportion to the order of g (s) for each expansion term. Become. That is, the amount of phase change due to g ² (s) is twice the amount of phase change due to g (s), and the amount of phase change due to g ³ (s) is three times the amount of phase change due to g (s). At the output terminal 4 of the reverb generator 10, a response (b)
A very complicated waveform is formed by superimposing a series of responses including (c) and (d). It can be seen that this is quite different from the simple impulse response of the conventional reverb generator shown in FIG. 7, that is, not including a phase shifter that causes dispersion in the feedback path. FIGS. 8 and 9 show an example of application of the reverb generator according to the present invention to a stereo reproducing apparatus. FIG. 8 shows an example in which the reverb generator having the configuration described in the above embodiment is connected to the left and right channels of a stereo playback device. In this case, the delay time ΔT _L , ΔT _R , transfer function
By adjusting g _L (s) and g _R (s) and the feedback gains K _L and K _R independently, the reproduced audio signal is adapted to the recording state of the recording signals of the left and right channels to optimize the sense of presence. be able to. FIG. 9 has a configuration in which the left channel output is supplied to the right channel input side via the attenuator K _L2 and the right channel output is fed back to the left channel input side via the attenuator K _R2 in addition to the configuration of FIG. The device shown in FIG. 9 can simulate complex acoustic effects such that the right and left channel sounds are reflected on the left and right walls of the concert hall, respectively. When these devices are used to simulate indirect sound in a multi-channel audio signal reproducing device as described in Japanese Patent Application No. 60-123630 filed by the present applicant, it is effective to enhance the sense of realism. In order to improve the sense of presence in the sound reproducing apparatus, the value of K is preferably about 0.2 to 0.4, depending on the recording state, and ΔT is preferably in the range of 5 to 150 milliseconds. Thus, the reverb generator according to the present invention has an advantage that a natural reverberation effect can be obtained even with a long time delay of up to 150 milliseconds, which was impossible with the conventional reverb generator. Further, in the reverb generating circuit according to the present invention, since the phase shifter 3 is included in the feedback path 8, a large dispersion effect can be obtained even if the number of connection stages of the operational amplifiers constituting the phase shifter is small. For example, in the phase shifter described in Japanese Patent Application No. 60-123630, at least 30 connection stages of operational amplifiers are required. However, in the phase shifter of the present application, no problem occurs even if it is reduced to 15th place. Further, in the transfer function of the equation (1), τ ₁ is set to be all constant. The same effect can be realized with a simpler circuit configuration. In this case, the adjustment of the reverb circuit can be made simple by adjusting only the parameters K, ΔT and τ. As described above, according to the present invention, a delay circuit means for adding a fixed time delay to an input audio signal input to an input terminal irrespective of frequency and outputting from an output terminal, and an output side of the delay circuit means An attenuator for attenuating an output signal output from the delay circuit in accordance with a predetermined attenuation constant and feeding back to an input side of the delay circuit, wherein the input terminal passes through the delay circuit to the output terminal. The following equation is included in the return path in series with the delay circuit means and in the return path returning from the output side of the delay circuit means to the input side of the delay circuit means through the attenuator means. Here, n is an integer of 2 or more, τi is a time constant, and s is a phase shift unit having a transfer function represented by a Laplace operator, whereby the effect of dispersion by the phase shift unit is enhanced, and the delay time of the delay circuit unit is increased. A reverb generator that can form a reverberation effect without causing an unnatural sensation even if it is made longer, increases the degree of freedom in adjusting the reverberation effect, and can adjust the reverberation effect over a wide range without causing an unnatural sensation. Can be When the reverb generator according to the present invention is applied to a sound reproducing device or a musical instrument, the sense of presence in a concert hall can be enhanced, and comfortable sound reproduction that cannot be obtained with a conventional hi-fi device can be realized. Also, even if the original recording is distorted, the reverb generator according to the present invention can improve the reproduced sound musically.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a reverb generator according to the present invention, FIG. 2 is an equivalent block diagram corresponding to the reverb generator shown in FIG. 1, and FIG. Is a Bode diagram showing an example of a frequency characteristic of the phase shifter of FIGS. 1 and 2 having a simplified transfer function g (s), and FIG. 4 is a phase shifter of FIG. 1 and FIG. FIG. 5 is a characteristic diagram showing a general example of the frequency characteristic of FIG. 1, FIG. 5 is a diagram showing an impulse response (dispersion) of the phase shifter of FIG. 1 and FIG. 2, and FIG. FIG. 7 shows an impulse response of a reverb generator having a phase shifter which causes dispersion in a feedback path, and FIG. 7 shows, for comparison, an impulse response of a conventional reverb generator which does not include a phase shifter which causes dispersion. FIGS. 8, 9 and 9 show the reverb generator according to the present invention applied to a stereo reproducing apparatus. FIG. 4 is a block diagram showing an example of a case where the operation is performed. DESCRIPTION OF SYMBOLS 1 ... Input terminal, 2 ... Delay circuit, 3 ... Phase shifter, 4 ... Output terminal, 5 ... Connection point, 6 ... Attenuator, 7 ... Addition connection point,
8: return path, 10: reverb generator.

Claims (1)

(57) [Claims] Delay circuit means for adding a fixed time delay to the input audio signal coming into the input terminal and outputting it from the output terminal irrespective of the frequency; and attenuating the output signal output from the output terminal according to a predetermined attenuation constant. A reverb generator comprising an attenuator means that feeds back to an input side of the delay circuit means, wherein the reverb generator is in series with the delay circuit means in a signal path from the input terminal through the delay circuit means to the output terminal. The following equation is included in the feedback path from the output side of the delay circuit means to the input side of the delay circuit means through the attenuator means and returned to the input side of the delay circuit means. However, n is an integer of 2 or more, τ _i is a time constant, and s is a reverb generator including phase shift means having a transfer function represented by a Laplace operator. 2. The time constant τ _i in the transfer function g (s) of the phase shift means
2. A reverb generator according to claim 1, wherein i is the same in the entire change range of i.