Apparatus for indicating the location of particular information, such as instructions, represented by predetermined signals previously recorded on a record medium. An array of light emitting sources is selectively energized to indicate the position of the particular information relative to the length of the record medium while the array is scanned in synchronism with the scanning of the record medium to detect the presence of such predetermined signals. Indexing means sequentially conditions each of the light emitting sources to be energized during scanning; and a temporary storage circuit stores a representation of a detected predetermined signal, until a light emitting source is conditioned.

Instruction indicating apparatus for a record and/or playback device

A binary encoded phase modulated signal (biphase signal) is demodulated by determining the period of time (T) elapsing between each two successive jumps in the level of the biphase signal; providing a clock frequency (B) approximately corresponding to the bit rate of the biphase signal with the aid of a clock generator; comparing the clock duration (1/B) of the clock frequency with the period of time (T) between each two jumps in level; and, with the aid of a sample and hold circuit controlled by the clock frequency (B), always ascertaining the logical value of the biphase signal and emitting a signal corresponding to the logical value whenever, immediately prior to a bit period, twice in succession, a value between 1/4 and 3/4 of 1/B is ascertained for the period of time (T), or a value between 3/4 and 5/4 of 1/B is ascertained for the period of time (T). Additionally, a signal characterizing interference can be emitted, or the output can be suppressed, if a value less than 1/4 of 1/B or greater than 5/4 of 1/B is ascertained as the period of time (T). This makes it possible, in the presence of a biphase signal, to recover the original data with high security in a relatively simple manner.

Method and/or apparatus for demodulating a biphase signal

In a video tape recorder having a tape on which are recorded "0" and "1" binary coded bits of a pulse width modulated signal as for identifying frames of a video signal also recorded on the tape, the tape being advanced past a head detecting the pulse width modulated signal at speeds variable with the fast forward, normal and slow motion mode of operation of the recorder so as to change the bit frequency of the pulse width modulated signal in correspondence with the speed of the tape, a circuit which demodulates the "0" and "1" bits of the detected pulse width modulated signal by comparing the coded pulse width of each succeeding bit (B i +1) with the width of the preceeding bit (B i ) to make the demodulation substantially independent of the bit frequency and the corresponding speed of the tape so that the circuit operates in each mode of recorder operation. In the preferred embodiment of the circuit, each bit is quantized into periodic pulses which correspond in number to the width of the bit. The number of pulses corresponding to the pulse widths of successive bits are then digitally compared in a comparator to obtain a two-level discrimination signal. More particularly, only selected higher value digits of the pulse numbers are compared to simplify the comparison and the comparator changes the level of the discrimination signal only during a preselected portion of each bit relative to the preceeding bit to assure accurate demodulation. The preferred circuit also has a circuit for deriving an edge pulse signal from the coded pulse width of each bit and a logic circuit operating on the edge pulse signal and the discrimination signal from the comparator for providing a signal corresponding only to bits of the one value, for example the "1" bits.

Circuit for demodulating a pulse width modulated signal

To decode a binary signal without regard to the speed at which it is read, each transition in the binary signal is detected, and the time lapse between successive transitions is determined to thereby establish the length of a pulse in the binary signal. The length of one pulse is compared with that of the immediately preceding bit cell to determine whether their lengths are approximately the same or vary by a factor of approximately 2, and any change in the binary state of the signal is determined accordingly. A multiplexing technique is employed to simultaneously decode a number of signals in this manner.

Demodulator for an asynchronous binary signal

For determining the address, in terms of its respective longitudinal time code, of a selected video or other information signal recorded on a tape which has both longitudinal time codes and control pulses or control track signals recorded along its length, when the information signal is selected while the tape is being moved at a speed which is insufficient for the reliable reading of its longitudinal time codes, the tape is accelerated to a speed sufficient for the longitudinal time codes to be reliably read and a subsequently encountered longitudinal time code is read, the reproduced control pulses are counted between the time that an information signal is selected and the time that the subsequently encountered longitudinal time code is read, and a derived address of the selected information signal is determined, in terms of its respective longitudinal time code, as a function of the value of the subsequently encountered longitudinal time code and the count of the reproduced control pulses.

Apparatus and method for determining time code addresses at low tape speed

The picture frames recorded on video magnetic tape are identified by serial binary numbers magnetically recorded along an edge of the tape. The sequential ONE and ZERO bits that form each number occur during equal successive intervals when the tape is transported at constant speed and these bits are detected as electrical pulse excursions, one pulse excursion during the interval for a ONE and no excursions during an interval for a ZERO. The pulses are detected even while the tape is not transported at constant speed as when it is accelerating or decelerating and so, the intervals for the successive binary bits may change rapidly and when that occurs, it is difficult to determine whether the successive excursions define a binary ZERO interval or the first half of a binary ONE interval and so, it cannot be determined whether they represent a binary ONE or a binary ZERO. In the present invention, the immediate or current interval between pulse excursions, herein called CT, and the immediately prior time between pulse excursions, referred to herein as PT, are compared and a series of logic steps are made with the following results: (1) when CT and PT are within a predetermined range of each other, then the current bit has the same binary sense as the prior bit; (2) when PT exceeds CT by at least a predetermined amount, then the current bit is a binary ONE; and (3) when CT exceeds PT by a predetermined amount, then the current binary bit is a ZERO.

Steven S. Chan

Papers

Digital video tape frame code readout system