JPH04220020A - Noise reduction circuit - Google Patents

Abstract

PURPOSE:To reduce noise having lots of peaks in a signal by connecting plural filters reducing each peak of noise on a frequency in series and inputting an output of a voice microphone to the series connection circuit. CONSTITUTION:Plural filters 12, 14, 16, 18 reducing each peak of noise on a frequency are connected in series. A voice output is inputted to the series connection filter circuit 10. Peaks of the noise are lost at an output stage of the circuit 10 and are smoothed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction circuit, and more specifically to a noise reduction circuit for a recording device added to a photographing device such as a video camera or a still camera.

0002

2. Description of the Related Art In photographing apparatuses such as those described above, noise is generated due to the driving of lenses, magnetic tapes, or magnetic disks. The audio microphones of recording devices attached to these photographic devices are designed to prevent input of these noises as much as possible. Specifically, (1) placing the audio microphone as far away from the photographic lens system and tape running system as possible, and (2) placing a cushioning material such as rubber between the audio microphone and the camera body. (3) Since the sound pressure level of the low frequency component of the above-mentioned noise is generally high, a method of cutting the low frequency part of the output of the audio microphone has been adopted.

0003

[Problems to be Solved by the Invention] However, as video cameras have become smaller, it has become difficult to take measures (1) and (2) above.

Furthermore, due to the diversification of lens configurations, in addition to the DC motors conventionally used as driving means for lenses and apertures,
Various motors such as pulse motors, voice coil motors, and ultrasonic motors have come into use. Each of these motors has its own unique vibration characteristics. For example, a pulse motor is disadvantageous in terms of noise compared to a DC motor, but its use is unavoidable due to the lens configuration, and new noise countermeasures must be taken.

[0005] When the noise generated when the lens is driven by a DC motor was analyzed using an FFT analyzer, it was found that the noise was approximately 85Hz.
The sound pressure level has a peak in the vicinity of 1 KHz, but the sound pressure level is approximately constant in the range from that to 1 KHz, and the sound pressure level is sufficiently usable in a video camera. On the other hand, if the lens is driven by a pulse motor, 0 to 1KH
Although the overall level in the z range was not much different from that of a DC motor, there were peaks at many frequencies, which gave a very audible sensation. FIG. 4 shows an average level change in frequency characteristics for a DC motor, and FIG. 5 shows an average level change in frequency characteristics for a pulse motor.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a noise reduction circuit that reduces noise having a large number of peaks.

[0007]

SUMMARY OF THE INVENTION A noise reduction circuit according to the present invention includes one or more filter circuits that reduce peak frequency components of input noise. Furthermore, it consists of a delay means that delays an input signal, and a subtraction means that outputs a difference signal between the input signal and the output of the delay means, and calculates the overall passing characteristic by calculating the peak frequency component of the noise contained in the input signal. It has a characteristic that reduces

[0008]

[Operation] By the above means, even if there is a peak in the frequency characteristics of the noise, it is leveled out and turned into so-called white noise. This makes it less noticeable to the auditory sense.

[0009]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic block diagram of an embodiment of the present invention. Before the audio microphone output is recorded by the recording circuit, the noise reduction circuit 10 reduces the peak components of the noise and equalizes it (ie, converts it into white noise). In the noise reduction circuit 10, 12, 14, 16, and 18 are the peak frequencies f1 and f2 of the noise to be reduced, respectively.
, f3, f4 characteristic frequencies f1, f2, f3, f
4.

Generally, in video cameras, the peak frequency of noise shown in FIG. 5 does not vary much among products. Therefore, for each product (or product group), the peak frequency f1,
Measure f2, f3,..., filters 12, 14, 1
It is only necessary to adjust the circuit constants 6 and 18.

FIG. 2 shows a specific example of the circuit of the filter 12. The filters 14, 16, and 18 may also have similar circuit configurations. 20, 22, 24 are resistors, 26, 28, 30 are inductances, 32, 34, 36 are capacitors, and 40, 42 are amplifiers. The constants of each element 20-36 are adjusted to obtain a desired characteristic frequency.

The operation of this embodiment will be briefly explained with reference to FIG. The audio output (specifically, the noise component) shown in FIG. 6(1) is passed through the noise reduction circuit 10 having the pass characteristic shown in FIG. 6(2). As a result, at the output stage of the noise reduction circuit 10, the peak of the noise disappears (or becomes smaller) as shown in FIG. 6(3), and the noise is leveled as a whole.

FIG. 3 shows another example of the circuit configuration of the noise reduction circuit. The microphone output is delayed by the delay circuit 44, and the subtracter 4
6, the microphone output that does not go through the delay circuit 44 is subtracted from the output of the delay circuit 44. By appropriately selecting the characteristics of the delay circuit 44, a passing characteristic as shown in FIG. 6(2) can be obtained.

[0015]

[Effects of the Invention] As can be easily understood from the above explanation, according to the present invention, noise components of voice input are leveled,
It can be made unnoticeable to the auditory sense.

[Brief explanation of the drawing]

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

2 is a specific circuit example of the filter 12 in FIG. 1. FIG.

FIG. 3 is another circuit configuration block diagram of the present invention.

FIG. 4 is a frequency characteristic diagram of noise caused by a DC motor.

FIG. 5 is a frequency characteristic diagram of noise caused by a pulse motor.

FIG. 6 is an explanatory diagram of the effect of this embodiment.

[Explanation of symbols]

Claims (2)

[Claims] 1. A noise reduction circuit comprising one or more filter circuits that reduce peak frequency components of input noise. [Claim 2] Comprising a delay means for delaying an input signal, and a subtraction means for outputting a difference signal between the input signal and the output of the delay means, the noise peak frequency component contained in the input signal is reduced. A noise reduction circuit characterized by having a pass characteristic.