JPS5911020A - Signal processing circuit - Google Patents

Abstract

PURPOSE:To attain ease of listening to minute sound quality of a low frequency for comparatively small sound volume, by expanding an input signal waveform to a frequency band of a prescribed frequency or below. CONSTITUTION:A signal inputted to an input signal terminal 1 selects one of paths 3, 4 of a switch 2. The signal of the path 3 is divided into the two paths, a low frequency signal is extracted from the one at an LPF6 and the amplitude of the signal is stretched by a stretching circuit 7, and a high frequency signal is extracted from the other signal at an HPF5. This signal and that from the circuit 7 are mixed at a mixing circuit 8. The signal obtained at the circuit 8 is a signal the amplitude at the low frequency only of which is expanded to the signal at the terminal 1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio amplifier, and more particularly to a signal processing circuit suitable for use in a tone control circuit of a preamplifier or control amplifier.

Conventionally, in audio amplifiers, the amplitude frequency characteristics of signals have been changed using tone controls and loudness controls. This is done to obtain sound quality that suits the user's preferences, or to enhance the bass range when the volume is low. Controlling the amplitude frequency characteristics means controlling the volume for each frequency range, and although this has a sufficient effect in this respect, it is still insufficient when sound quality is taken into account.

That is, in human hearing, the equal loudness curve (equal sensitivity frequency characteristic curve with respect to sound pressure) changes depending on the volume, but at the same time, the time constant of the response to the signal changes. For example, for a 500/72 signal, the response time constant is 50 milliseconds when the sound pressure level is 55 dD.
At 35 dB, it is 110 milliseconds. Also, 1xHz
For a signal of 110 at a sound pressure level of 55 dB,
However, at 35 dB, it is 620 milliseconds.

This change in time constant means that minute sounds that can be heard at relatively high volumes become inaudible at low volumes. I- Therefore, if the signal is controlled so that minute sounds can be heard at low volumes, the sound quality at relatively high volumes can be enjoyed. From my experience, the audible frequency range is 20H! At -20 KHz, it is effective to expand the amplitude change so that minute sounds can be heard below about 500 Hz.

An object of the present invention is to provide a signal processing circuit that expands the amplitude of a signal inside a control amplifier in order to make it easier to hear minute sound quality when the volume is relatively low as described above. .

In the present invention, in order to compensate for the low pitch feeling that occurs at relatively low volumes, first a bypass and low-pass filter are used to form a signal with a relatively low frequency and a signal with a high frequency from the input signal, and then a signal with a relatively low frequency and a signal with a high frequency are formed. The above object is achieved by expanding the amplitude of a signal at a high frequency range using an expansion circuit, and mixing this signal with the above-mentioned signal at a high frequency range.

An embodiment of the present invention will be described below. FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 1 shows a block diagram for processing signals in one channel signal path of two stereo channel signal paths. In the figure, a signal input from an input signal terminal 1 causes a switch 2 to select one of two paths 3.4. Path 3 is a path for performing signal processing according to the present invention, and path 4 is directly connected to output terminal 9 without performing signal processing. The signal on path B is divided into two paths, one of which takes out the low frequency signal through a low pass filter 6 and expands the signal amplitude through an expansion circuit 7. On the other hand, from the signal on path 3, a high frequency signal is extracted by bypass filter 5, and this signal is combined with the above-mentioned expander 7.
The mixing circuit 8 mixes the signals.

The signal obtained here is a signal whose amplitude is expanded only in the low frequency range with respect to the signal at the input terminal 1.Next, the characteristics of the above filter will be explained using FIG.

The cutoff frequency of the low pass filter and bypass filter is 500Hz. This value is due to the fact that the magnitude of the signal amplitude does not affect the auditory sense, and the effect is most noticeable in the low frequency range, and as the signal becomes smaller, the auditory loudness becomes smaller and smaller. It is an empirical fact that signal processing at a frequency of about 500 Hz or less is effective.

Next, the characteristics of the expander will be explained. In FIG. 5, the horizontal axis represents the input signal amplitude, and the vertical axis represents the output signal amplitude. The straight line a in the figure represents a linear relationship, and represents the characteristics of a simple amplifier with a gain of 1. In contrast, the curves in the figure represent the characteristics of the stretcher. In the case where the amplitude is relatively small as shown in the figure, there is an expansion effect and there is a maximum expansion rate of 6 dB, but when the input signal becomes larger than a certain amplitude, the output signal amplitude is saturated and becomes a constant amplitude. Did you?
The signal processing circuit of the present invention is effective when the input signal has a relatively small amplitude.

For this reason, it is effective to use switch 2 in FIG. 1 in conjunction with the volume of the preamplifier or control amplifier.

Further, it is effective to use the signal processing circuit described above in combination with a conventional tone control circuit, loudness control circuit, etc.

Next, another embodiment of the present invention will be described using FIG. 4.

In the figure, the input signal from input terminal 1 is divided into two paths,
The method of passing one of the signals through the bypass filter 5 is the same as in the case of FIG. . The first method is to mix this signal with the output signal of the bypass filter 5.
It is the same building as the one shown in the figure. The same effect can be obtained with such a circuit configuration.

According to the present invention, by expanding the input signal waveform by a maximum of 6 dB in the frequency range of approximately 500 Hz or less, it has become possible to magnify and hear minute changes in sound quality at low frequencies. This has the effect of enhancing the bass sound and improving the quality.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a graph showing the characteristics of the filter in Fig. 1, and Fig. 6 shows the characteristics of the expansion circuit in Fig. 1. FIG. 4 is a block diagram showing another embodiment of the present invention. Explanation of symbols 5... Bypass filter, 6... Low pass filter, 7... Expander, 8... Mixing circuit. 1'1 Mouthfulness 3 Kyousen 4ki

Claims (1)

[Claims] 1) A low-pass filter and a bypass filter provided in parallel with the input signal, an expansion circuit for expanding the amplitude provided on the output side or input side of the low-pass filter, and the output signal of the expansion circuit and the bypass filter. 1. A signal processing circuit comprising: a mixing circuit for mixing an output signal of