JPS636799Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a means for arbitrarily adjusting the reverberation time of an echo circuit, and its purpose is to adjust only the reverberation time without changing the signal output level of the echo circuit. The purpose of this research is to propose a variable circuit that can be used.

In audio equipment, mechanical echo devices using coil springs were used to give an echo effect to the playback signal. However, since this mechanical device is prone to generating noise when subjected to external impacts, echo circuits using bucket brigade devices (hereafter referred to as BBD), which are analog signal delay elements, have recently come to be widely used.

A so-called BBD is an LSI in which many transistors and capacitors are arranged alternately, and the charge corresponding to the input signal is sequentially transferred in a bucket brigade style using clock pulses, thereby delaying the input signal by a certain period of time. It is also possible to output a signal and change its delay time arbitrarily.

FIG. 1 shows a block diagram of a conventional echo circuit using a BBD. This echo circuit consists of a signal input terminal 1, an adder 2, an amplifier 3,
Low pass filter 4, BBD 5, low pass filter 6, amplifier 7, variable resistor VR, adder 8, signal output terminal 10, the above amplifier 7 and variable resistor VR
The attenuator 9 is connected between the connection point between the adder 2 and the adder 2, and the signal system is connected between the signal input terminal 1 and the adder 8.

In the above circuit, the input signal applied to the signal input terminal 1 is directly applied to the adder 8 and also to the adder 2, amplified by the amplifier 3, and applied to the BBD 5 via the low-pass filter 4.

In this case, the input signal is delayed by a predetermined time (for example, 50 msec) while the charge is transferred through multiple stages (for example, 1024 stages) by the BBD 5, and then passed through the low-pass filter 6, amplified by the amplifier 7, and then connected to the variable resistor. The level is adjusted by VR and added to the adder 8.

On the other hand, the output of the amplifier 7 is lowered in level by the attenuator 9 and then fed back to the adder 2, and the delay operation of the BBD 5 for the same signal is repeated.
The signal output terminal 10 outputs a delayed signal that is at the same level as the input signal and that is attenuated after a certain reverberation time (for example, 2 seconds) following a non-delayed signal.

Note that a clock pulse is supplied to the above BBD5 from a clock pulse generator (not shown).
The charge transfer period inside the BBD is determined by the clock frequency, so changing the clock frequency can change the signal delay time, but the clock frequency is usually set to a relatively low frequency (8 kHz) to make the delay time as long as possible. degree). Therefore, the reverberation time of the echo circuit shown in FIG. 1 is adjusted by the variable resistor VR, and FIG. 3 shows the relationship between the output level of the delayed signal appearing at the signal output terminal 10 and the reverberation time. show.

If the variable resistor VR is adjusted to change the output level of the delayed signal at time t ₀ in three steps, for example, as shown in Figure 3, the time it takes for the signal to reach the 0 level becomes almost constant, but the signal The detection limit, that is, the time to reach the noise level a is t ₁ , t ₂ , t ₃
The reverberation time increases as the signal level at t ₀ increases.

In other words, in conventional echo circuits, it is necessary to change the signal output level in order to adjust the reverberation time, and to maintain a predetermined output level, the level must be readjusted using a separate level adjuster (not shown). The drawback was that I had to do it.

This invention is an improvement over the conventional problems as described above, and FIG. 2 shows a circuit of one embodiment of the invention, and the same parts as those of the conventional example are given the same symbols and the explanation thereof will be omitted. In the circuit shown in FIG. 2, a series circuit of a resistor R and a capacitor C is connected between the output terminal of the amplifier 7 and the adder 8 in the conventional circuit.
A variable resistor is connected between the connection point of the adder 8 and the ground.
VR is connected, and the output signal of the amplifier 7 is fed back to the adder 2 from the connection point between the capacitor C and the variable resistor VR via an attenuator 9.

In the above circuit, the resistor R, capacitor C, and variable resistor VR form a high-pass filter 11, and by adjusting the variable resistor VR, the cut-off frequency of the high-pass filter can be changed.

Figure 4 shows the frequency characteristics of low-pass filters 4 and 6 inserted into the BBD circuit, and the frequency characteristics of high-pass filter 11. 6dB/ for the frequency of
It has an octave attenuation characteristic, and on the other hand, the frequency characteristic of the high-pass filter 11 changes as shown by curves C ₁ , C ₂ , and C ₃ by adjusting the variable resistor VR, and the resistance value of the variable resistor VR changes. The smaller the value, the higher the cutoff frequency.

FIG. 5 shows the relationship between the delayed signal output level and the reverberation time of the circuit according to the embodiment of this invention. When the high-pass filter characteristic in FIG. 4 is curve C ₁
Since almost all frequency components of the BBD output are output, the reverberation characteristics will be as shown by curve d ₁ in Figure 5, and if the high-pass filter characteristics are curve C ₂ , some reduced frequency components will be cut out. As a result, the reverberation characteristics are as shown by curve _d2 , and similarly, when the high-pass filter characteristics are curve _C3 , most of the low frequencies are cut out, resulting in the reverberation characteristics as shown in curve _d3 .

Note that the frequency characteristics of the high-pass filter 11 are C ₁ , C ₂ , C ₃ when the resistance value of the variable resistor VR is lowered.
However, as mentioned above, since the value of the resistor R is sufficiently small compared to the resistance value of the variable resistor VR, the signal level applied to the adder 8 hardly changes, and the time t ₀ The signal output level at is almost constant as shown in FIG.

However, the frequency characteristics of the high-pass filter 11 are
By changing C ₁ , C ₂ , and C ₃ , the passband of the output signal from BBD becomes gradually narrower.
In particular, the output level for audio signals is the curve d ₁ ,
The degree of temporal attenuation increases in the order of d ₂ , d ₃ , and the reverberation time until reaching noise level a is t ₃ , t ₂ ,
It gets shorter in the order of t ₁ .

Note that curve C ₄ in Figure 4 shows the case where the resistance value of the variable resistor VR is lowered to almost equal to the value of the resistor R, and the pass band of the BBD output signal becomes extremely narrow, so the attenuation of the output signal is As shown in curve d ₄ in Figure 5, the reverberation time becomes shorter and the time
The output level at t ₀ also decreases.

That is, the circuit of the embodiment of this invention can change only the reverberation time while keeping the output level at time _t0 almost constant in the normal frequency range, but it is also possible to set both the reverberation time and the signal output level to zero by adjusting the variable resistor VR.

As described above, the variable reverberation time circuit of this invention changes the passband of the BBD output signal by changing the cutoff frequency of the variable high-pass filter, and thereby changes the attenuation curve of the delayed signal output. It is characterized by adjusting the reverberation time.

In addition, in echo devices, it is generally said that the lower the frequency, the larger the auditory echo effect, so the circuit of this invention is designed to increase the low frequency components in the output signal as the reverberation time increases. A configuration has been adopted.

The variable reverberation time circuit of this invention can arbitrarily adjust the reverberation time while keeping the output level almost constant, so there is no need to readjust the signal level in the subsequent circuit, which is not only convenient for operation, but also reduces the reverberation time. Since the frequency characteristics of the output signal change depending on the length of the circuit, there is also the advantage that the perceptual echo effect becomes more pronounced than in conventional circuits.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional echo circuit, Figure 2 is a block diagram of a conventional echo circuit.
Figure 3 is a block diagram of one embodiment of the echo circuit of this invention, Figure 3 is a diagram showing the reverberation characteristics of the output signal of the conventional circuit, and Figure 4 is the frequency of the low-pass filter and high-pass filter of the circuit of the embodiment of this invention. FIG. 5 is a diagram showing the reverberation characteristics of the output signal of the circuit according to the embodiment of this invention. 1...Input signal terminal, 2, 8...Adder, 3,
7...Amplifier, 4,6...Low pass filter, 5
...BBD, 9...Attenuator, 10...Signal output terminal, 11...High pass filter, VR...Variable resistor, R...Resistor, C...Capacitor.

Claims (1)

[Scope of utility model registration request] An analog signal delay element such as a bucket brigade device, a low-pass filter inserted on the input side and output side of this analog signal delay element, an adder to which the input signal and the delayed signal are applied, and a delay to the adder. The echo circuit consists of an attenuator inserted in the signal return path, and outputs a delayed signal that attenuates after a predetermined reverberation time when an input signal is applied. A reverberation time variable circuit in an echo circuit configured to change the reverberation time of a delayed signal output by changing the cut-off frequency of the high-pass filter using a variable resistor.