1. Field of the Invention
The present invention relates to a noise killing circuit for video tape duplicating apparatus and, more particularly, is directed to a color noise killing circuit for duplicating apparatus with capability of two mode duplication.
2. Description of the Prior Art
A video tape duplicating apparatus also known as a dubbing machine is for making a duplicate of information recorded on a video tape onto another medium of recording.
The conventional duplicating apparatus is one assembled by connecting two video tape recording and playing apparatuses to each other and, particularly, it is generally called "double deck video tape recorder" which is composed of the two apparatuses within a housing.
A video tape recorder consists of a recording system which records an image information onto a video tape and a play back system which reproduces the recorded image information on the tape.
In such a duplicating apparatus, duplicating procedure is effected by way of recording the image information reproduced from the play back system of one apparatus onto the recording system of another apparatus.
In the play back system PB shown in FIG. 1, the mixed image signal recorded on the video tape T1, in the form of intermixture of color signal and luminance signal each having been subjected to modulation, is picked up via the play back head H1, and thereafter is separated into color signal and luminance signal. (Y/C separation)
Both the separated luminance signal and color signal are to be respectively subjected to demodulation and modulation to be changed into the respective demodulation signals Yn and Cn (referred to as Y/C demodulation), and then, those are transmitted in the form of mixture to the display apparatus or the like.
The recording system receives and Y/C separates the output signals and modulates the respective separated signals and then mixes the modulated signals, so that the resultant signals are recorded onto the video tape T2 via recording head H2, thereby completing the duplicating procedure for a video tape. Such a duplicating apparatus as described above will function well by simply connecting the respective input and output terminals of two apparatuses.
The drawback of this known system resides, however, in the fact that quality deterioration of the duplicated images often occurs due to the long transmitting path through which the reproduced image signals are transmitted for the demodulation--modulation process.
To cope with the defect, a method for improving the duplicated image quality has been proposed which directly connects the respective image signals Cf and Yf, which have been Y/C separated in the play back system, to the mixer of the recording system.
When such duplicating modes are performed in a duplicating apparatus, the former will hereinafter be referred to as a normal copy mode and the latter as a fine copy mode, respectively. The deterioration of picture quality is prevented by duplicating during the fine copy mode especially for the direct repeat duplication of photographed video tapes or the tapes.
In case that the video tape of the play back systems is recorded with only black-and-white picture information, the playing back image signal is only of luminance signal and no color signal is generated therefrom.
Here, noises generated from the color signal transmitting path cause no problems, in the normal copy mode, since those are eliminated during the courses of modulation and demodulation process.
However, in the case of the fine copy mode operation, there has always arisen such a problem that the quality of the recorded pictures is degraded because the above prescribed noises are directly induced to the play back system and mixed with the recorded luminance signal to affect the properties of recording.