# US 5,345,344 A · System and method for removing noise when switching between heads in a digital video cassette recorder

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- Number: US 5,345,344 A
- Document ID: US5345344A
- Status: Granted
- Kind: A
- Application number: 07/879,901
- Filed: 1992-05-08
- Granted: 1994-09-06
- Earliest claimed: 1991-05-14
- Assignees: Goldstar Co., Ltd.
- Inventors: Ja T. Kim
- Web page: https://patentgrep.com/patent/US5345344A

## CPC

- G11B 15/14: Masking or switching periodically, e.g. of rotating heads
- G11B 5/00865: {for transducing on more than one segment simultaneously}
- G11B 20/20: for correction of skew for multitrack recording
- G11B 20/24: for reducing noise {(control of amplification in general, e.g. dependent upon noise level H03G)}
- G11B 20/00992: {Circuits for stereophonic or quadraphonic recording or reproducing}
- G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R)

## Abstract

Audio playback system and method for a Hi-Fi VCR capable of preventing an occurrence of noise when audio heads are switched. When an azimuth occurs with respect to each arrangement angle of audio heads or when one of audio signals played back audio heads is delayed due to the elasticity of VCR tape, a correction signal generator detects a phase difference between the audio signals and corrects error in the audio signals according to the detected phase difference. By switching units, error corrected audio signals are switched and combined into continuous audio signals, each corresponding to a stereo channel. As a result, it is possible to avoid an occurrence of noise at a portion at which audio signals of the same stereo channel are connected.

## Claims

### Claim 1

An audio playback system for a video cassette recording comprising:
a plurality of audio heads arranged on a drum and adapted to play back alternately audio signals recorded on a cassette tape according to a rotation of the drum;
amplifying means for amplifying respective audio signals played back by the audio heads;
filtering means for filtering amplified audio signals to separate each audio signal into audio signals corresponding to first and second stereo channels, respectively;
digital demodulating means for digitally demodulating the audio signals corresponding to the first and second stereo channels;
correction signal generating means for detecting a phase difference between the demodulated digital audio signals and generating a correction signal for correcting the phase difference;
memory means for storing the demodulated digital audio signals temporarily, correcting an error caused by the phase difference according to the correction signal from the correction signal generating means and then outputting error corrected digital audio signals; and
switching means for switching digital audio signals from the memory means to combine them into continuous digital audio signals each corresponding to each stereo channel, respectively.

### Claim 2 (depends on 1)

An audio playback system for a video cassette recorder as set forth in claim 1, wherein the memory means comprises a plurality of random access memories.

### Claim 3 (depends on 1)

An audio playback system for a video cassette recorder as set forth in claim 1, wherein the filtering means comprising a plurality of band pass filters having different frequency bands each corresponding to each stereo channel.

### Claim 4

An audio playback method for a video cassette recorder having a plurality of audio heads, comprising the steps of:
detecting audio signals from a cassette tape, by using the audio heads alternately;
filtering each detected audio signals to produce audio signals corresponding to two stereo channels, respectively, and digitally demodulating the audio signals corresponding to the stereo channels;
storing the demodulated digital audio signals temporarily;
detecting a phase difference between the demodulated digital audio signals and correcting the temporarily stored digital audio signals according to the detected phase difference;
switching outputting of the corrected digital audio signals to combine them into a continuous digital audio signal corresponding to each stereo channel and outputting the continuous digital audio signal.

### Claim 5 (depends on 4)

An audio playback method for a video cassette recorder as set forth in claim 4, wherein the step of correcting the digital audio signals according to the detected phase difference comprises the steps of:
determining a digital audio signal having a finally succeeding phase among digital audio signals, as a reference signal; and
delaying each digital audio signal other than the reference signal for a delay time corresponding to a phase difference between each digital audio signal and the reference signal.