Dynamic magnetic information storage or retrieval – Record copying
Patent
1989-10-13
1992-04-07
Envall, Jr., Roy N.
Dynamic magnetic information storage or retrieval
Record copying
358336, 360 381, H04N 594
Patent
active
051033496
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention is based on a process for copying frequency modulated recorded on magnetic storage means signals, wherein a FM signal is retrieved from the storage means, amplified, filtered, limited to a constant amplitude and again recorded.
During the editorial processing of television shows which are stored on a magnetic tape, it is frequently required to change the content of the original recording in a plurality of steps so as to finally receive a transmittable show. Intermediate copies serve for retaining the given state of the change as a basis for the further processing. Therefore, the final result is a recorded magnetic tape, whose individual scene segments were very often editorially changed and copied. It is also a requirement that the determination of the signal quality should remain within established limits, even after multitude of playbacks or copying.
Signals, in particular television signals which for the purpose of the magnetic recording have been modulated on a carrier frequency are copied in accordance with the state of the art in that the signals which are being picked up from the magnetic tape in the reproduction device are amplified, regenerated, limited, corrected as to timing errors and dropouts and are finally demodulated. After transmitting to the recording device, the demodulated signals must again be filtered, distorted, amplified and modulated upon a carrier frequency and finally be recorded to a magnetic tape by electromagnetic converters (magnetic heads).
The known and customary process is disadvantageous in that the original signal distorts due to the repeated application of the operations.
In order to obtain a copy with a rather high quality it is required to reduce the number of operations (modulation operations, demodulation operations, time error corrections etc) to which the signal is subjected to since these operations result in a deterioration of the signal quality. It is therefore advantageous to remain within the range of the carrier frequency signal during the copying operations and not, as hitherto customary, in the video signal range. Thus, the video quality deteriorates only at a minimum after a copying procedure, or expressed in other words, with the same requirements for the video quality, after a multiple copying operations, the number of copies (generations) is increased. A reason why this process had not yet been used resides in the fact that the preparation of the carrier frequency signals before the new recording presents difficulties. The biggest problem is the treatment of dropouts during the FM-copying. The solving of this problem is also the object of this invention.
Basically it is possible to perform a dropout compensation of frequency modulated signals; because of the requirement of an interference free transition located without phase intermittency between the reproduced and inserted signals this is very difficult to achieve. Another possibility is the use of an auxiliary track on which the dropout information would h=recorded parallel to the FM-signal. However, this possibility is eliminated for economic considerations (poor use of the storage surface on the magnetic tape).
ADVANTAGES OF THE INVENTION
The process for storing frequency modulated signals in accordance with the invention has the advantage that independently from the number of playbacks, the original signal is subjected only once to the operations, which are prerequisite for the efficient recording on a magnetic tape and the playback from the magnetic tape.
A further advantage is considered to be that the time transformation operations to which the signal to be recorded had been subjected and the reciprocal return transformation also are only performed once during recording and final playback.
It is particularly advantageous that the additive and cumulative error propagation is substantially reduced due to the reduction of the required operations during copying.
DRAWING
A circuit for performing the inventive process is illustrated in the drawing and is explain
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BTS Broadcast Television Systems GmbH
Envall Jr. Roy N.
Striker Michael J.
Young W. R.
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