Patent GB-1159881-A (GB)
Title: Electronic Editing System for Helical Scan Video Tape Recorder
IPC: G11B27/029
Filed: 1967-01-03
Abstract: 1,159,881. Electronic editing of magnetic video tape. AMPEX CORP. 3 Jan., 1967 [3 Jan., 1966], No. 266/67. Heading G5R. The invention is an electronic editing system for a helical scan video tape recorder. The recorder includes tape supply and take-up reels on a deck and a helical scanning assembly mounted on the deck and having a guide for guiding the tape between the reels in a helical path about a rotary head drum having at least one (preferably two) video RF heads mounted thereon. A motor-driven capstan is mounted on the deck for moving the tape between the reels. The head drum is driven by a separate motor, and tachometer means are driven by the drum for generating tachometer pulses representative of drum position. A video erase head is mounted on the deck transverse to the tape at a position upstream from the scanning assembly and has an erase oscillator coupled to it. A video record section is coupled to the video RF heads. A head drum servo is coupled to the head drum motor to control it in accordance with a head drum error signal developed by comparison of signals at first and second inputs thereof; a capstan servo is coupled to the capstan motor for controlling it in accordance with a capstan error signal developed by comparison of signals at first and second inputs of the capstan servo. A control track head is mounted on the deck to record a control track on the tape or play it back. The editing system comprises an editing mode selector switch having " normal," " short insert," " long insert " and " assemble " mode positions; an edit record switch coupled to the editing mode selector switch applies, upon actuation, triggering impulses at the selected positions of the latter. Logic circuitry couples the editing mode selector switch to the video record section, erase oscillator, head drum servocapstan servo, tachometer means and control track head. The logic circuitry includes means normally connecting the tachometer means to the first input of the head drum servo, and a reference source to the second input of it; the logic circuitry also includes means normally connecting the first input of the capstan servo to the tachometer means and the second input of it to the control track head. The editing mode selector switch in the " normal " position decouples the edit record switch from the logic circuitry. In the " short insert " position the logic circuitry includes means interconnected to energize in response to a first of the above-mentioned triggering impulses, the video record section with a new video signal to be recorded, and, in response to a second of these impulses, to de-energize the video record section. In the " long insert " position the logic circuitry includes means interconnected to energize simultaneously in response to a first impulse, the video record section and the video erase oscillator, and in response to a second impulse, to de-energize video erase oscillator and after a predetermined delay de-energize the video record section. In the " assemble " position the logic circuitry includes means interconnected to energize simultaneously in response to a first impulse, the video record section and video erase oscillator, connect the second input of the head drum servo to a source of vertical sync. from the video signal for recording, connect the output of the capstan servo to a nominal speed reference potential, connect the second input of the capstan servo to its output, and disconnect the control track head from the second input of the capstan servo and connect the control track head to the tachometer means; in response to a second impulse the video record section and video erase oscillator are deenergized, the second input of the head drum servo is re-connected to the reference source, the output of the capstan servo is disconnected from the nominal speed reference potential the second input of the capstan servo is disconnected from its output, and the control track head is disconnected from the tachometer means and reconnected to the second input of the capstan servo. Thus, when the editing mode selector switch is placed in the " short insert " position, and the edit record switch is first actuated, the video record heads are energized with the new video signal, but the erase head is not energized. The capstan and head drum servos are maintained in a playback mode so that the new signal closely tracks the existing signal and is recorded over the latter. The video heads are de-energized to terminate the " short inset" by a second actuation of the edit record switch. For the "long insert" editing operation, the video record heads are energized and the capstan and head drum servos are maintained in playback mode as above, but the video erase head is energized, simultaneously with the record heads. An in-going splice 81, Fig. 3, is thus effected, on the downstream side of which the existing signal is represented by o's 79 and on the upstream side of which the new signal recorded over the existing signal is represented by x's. The line Y of the tape was adjacent the video erase head when it was energized, so that upstream of this line only the new signal, represented by dots, appears. The out-going splice line is shown at 82. The original audio tracks 84 and 86 are shown by solid bars, the new ones by dotted bars 84, 86. For the " assemble " editing operation, the video record heads and erase head are simultaneously energized, but the error signal normally used to control the capstan servo in the playback mode of the apparatus is de-coupled from the input of this servo and a constant signal commensurate with nominal tape speed is applied thereto. Simultaneously, the control track head is switched to the record state and coupled in receiving relation to the head drum tachometer. The control track head thus records the tachometer pulses on the tape, beginning at line Z, Fig. 4, as a new control track 83, shown dotted, for controlling tape position during playback of the new video material. Thus, phase match between the original control track and the start of the new control track is obtained. An in-going splice 81 is shown as before. When the edit record switch is next energized, the video record heads and the erase head are de-energized simultaneously, and the capstan servo and control track head are switched to their original playback conditions. Preferably the circuitry includes provision for recording the video signal without audio, or the video signal with one or other of two audio signals, or the video signal with both audio signals. Indicator lamps for all states of the apparatus are provided.