GB1593826A

GB1593826A - Video signal speed-change reproducing system

Info

Publication number: GB1593826A
Application number: GB1227178A
Authority: GB
Original assignee: Victor Company of Japan Ltd; Nippon Victor KK
Current assignee: Victor Company of Japan Ltd; Nippon Victor KK
Priority date: 1977-03-30
Filing date: 1978-03-29
Publication date: 1981-07-22
Also published as: FR2386096A1; DE2813576B2; AT377149B; ATA226878A; DE2813576C3; JPS53120327A; CA1132249A; JPS5840873B2; DE2813576A1; FR2386096B1

Description

(54) VIDEO SIGNAL SPEED-CHANGE REPRODUCING SYSTEM (71) We, NIPPON VICTOR KABUSHIKI KAISHA, of No.12, 3 Chome, Moriya-Cho, Kanagawa-Ku, Yokohama-City, Kanagawa-Ken, Japan, a Japanese Corporation, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: The present invention relates generally to video signal speed-change reproducing systems and more particularly to a video signal speed-change reproducing system for reproducing a video signal recorded on mutually adjacent tracks alternately with two heads of mutually different azimuth angles, the video signal being thus reproduced at a speed differing from that for the recording.

The term "video signal speed-change reproducing system" as used herein means a system for reproducing a video signal from a magnetic tape, on which a video signal has been recorded, which travels at a speed different from that for normal reproduction and recording.

In the prior art, a system wherein a video signal is recorded on a magnetic tape on parallel tracks formed obliquely to the longitudinal direction of the magnetic tape, and this tape is caused to travel at a tape speed different from that at the time of recording or to stop thereby to carry out speed-change reproduction such as quickmotion reproduction, slow-motion reproduction, or still picture reproduction has been known. In this system, since the tape speed at the time of reproduction is different from that at the time of recording, the tracing path of the head relative to the tape during reproduction differs from the tracing path (track) of the head during recording.

On one hand, in a conventional video signal recording and reproducing system, ordinarily, recording is carried out on a recording medium by forming a track thereon in manner to leave an unrecorded zone or band called a guard band between neighboring tracks in order to prevent the generation of beats caused by the reproduced signals of neighboring tracks due to tracking deviation of the head at the time of reproduction. When a tape recorded in this manner is played back by speed-change reproduction as described above, the head traces over the track and the unrecorded band. When the head traces over the unrecorded band, the reproduced signal is remarkably lowered in level or disappears, and, for this reason, a noise is generated in the reproduced picture.

Accordingly, it is possible to so select the tape speed that this noise will be at an inconspicuous position on the picture screen, but there has been a problem due to the narrow variable range of the tape speed.

For example, it is not possible to increase the tape speed three times the ordinary speed and, at the same time, to place the noise always at an inconspicuous position on the picture screen. Furthermore, in the above mentioned system, since unrecorded bands are provided between tracks, the utilization efficiency of the tape has been poor.

In addition, there has been a system wherein the angle of inclination of the tape relative to the head rotating plane is varied in accordance with the tape speed so that the heads will trace accurately over the track at the time of speed-change reproduction.

However, this system has been accompanied by the problem of the complexity of the mechanism for varying the inclination angle of the tape in this manner, which gives rise to high cost of the apparatus, and by the difficulty of accurate tracking in actual practice.

On the other hand, the present application has previously proposed a system wherein tracks are formed on a tape without gaps between neighboring tracks, and, moreover, a color video signal can be recorded and reproduced without the occurrence of beat disturbance, in British Patent No. 1506087 entitled "Color video signal recording and/or reproducing system".

In this previously proposed system, a pair of azimuth heads having gaps which are inclined with a certain azimuth angle in mutually opposite directions with respect to the direction perpendicular to the longitudinal direction of the track are used, and neighboring tracks are formed in contiguous contact side-by-side without a gap therebetween, Furthermore, the phase of the chrominance signal is shifted by 90 degrees for every horizontal scanning period, and, moreover, the direction of this phase shifting is reversed from one track to the neighboring track, In accordance with this system, the tape utilization efficiency is high since the tracks are in close contact with each other, and, moreover, there is no occurrence of beat disturbance.

According to the invention, there is provided a video signal speed-change reproducing system comprising: a tape on which a video signal has been recorded with tracks disposed contiguously and obliquely relative to the tape longitudinal direction, said tracks being recorded and formed by a plurality of rotating heads having gaps at mutually different azimuth angles; means for causing said tape to travel at a speed V represented by the equation n+2 V = Vot n ) wherein Vo is the tape speed for normal reproduction (and recording), and n is a positive integer, and for causing the tape to be stopped during still picture reproduction; and reproducing means having a plurality of rotating heads having gaps at mutually different azimuth angles which are the same as said azimuth angles of the recording heads and arranged to successively scan said tracks of the tape thereby to reproduce said recorded video signal from the tracks formed by the recording head having the gap at one of the different azimuth angles by means of the rotating head having the gap at the one azimuth angle and from the tracks formed by the recording head having the gap at the other azimuth angle by means of the rotating head having the gap at the other azimuth angle.

It is thus possible to provide a system for speed-change reproduction of video signals in which any noise bar due to a lowering of the reproduced signal on the reproduced picture is always at an inconspicuous position on the picture screen, and, moreover, a wide speed-change range can be used. In this system, the tape utilization efficiency is also high. By selecting the tape speed at a specific value at the time of reproduction, the noise bar is caused to be produced always at a certain position on the picture screen. Furthermore, by selecting the relative scanning phases of the heads on the tape to have a specific relationship to the tape, the noise bar can be caused to be at an inconspicuous or invisible position on the picture screen. In addition, the speedchange range can be made wider than that in a known system.

It is also possible to provide a system for speed-change reproduction of video signals in which reverse reproduction by reversing the direction of tape travel is also possible.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a block schematic diagram of one embodiment of the system for speedchange reproduction of video signals according to the invention; Figures 2(A) through 2(G) are diagrams respectively indicating the waveforms of signals at various parts of the system shown in Figure 1; Figure 3 is a block diagram of one example of an automatic correction circuit for reverse tracking; Figures 4A and 4B are respectively a diagram indicating the scanning track pattern at the time of triple-speed fast (quick) motion reproduction and a graph indicating the variation with time of the level of the reproduced signal; Figures 5A and 5B are respectively similar to Figures 4A and 4B for the case of double-speed, fast motion reproduction; Figures 6A and 6B are respectively similar to Figures 4A and 4B for the case of fast motion at 3/2 speed; Figure 7 is a diagram indicating the scanning track pattern at the time of halfspeed slow motion reproduction; Figures 8A and 8B are respectively similar to Figures 4A and 4B for the case of 1/3 speed slow motion reproduction; Figure 9 is a diagram indicating the scanning track pattern at the time of still picture reproduction; and Figure 10 is a diagram indicating the scanning track pattern at the time of reverse normal-speed reproduction.

Referring first to Figure 1, a video signal to be recorded is introduced into the system shown through an input terminal 11 is passed through a recording and reproducing circuit 12 and supplied to a pair of recording and reproducing video heads 13a and 13b and a vertical synchronizing signal separa tion circuit 14. The video heads 13a and 13b have mutually opposite azimuths as described hereinafter and are mounted on diametrically opposite sides of a rotary drum 16 rotated at a rotational speed of 30 rps. by a motor 15. A magnetic tape 18 is wrapped obliquely around the rotary drum 16 and a stationary drum 17 and is driven to travel in the arrow direction X by a capstan 19 driven by a motor 20 and a pinch roller 21. A video signal is recorded by the video heads 13a and 13b alternately along tracks on the tape 18, successively one field per track, the tracks being positioned contiguously to each other and obliquely relative to the longitudinal direction of the tape.

On the other hand, a vertical synchronizing signal of 60 Hz which has been separated from the video signal in the vertical synchronizing signal separation circuit 14 is passed through an amplifier 22 and supplied to a monostable multivibrator 23, where its frequency is halved to 30 Hz. The resulting output signal is passed through a recording amplifier 24 and supplied to an attenuator 25 and, at the same time, by way of a switch 26 with its moving contact connected to a contact point a to a control head 27, by which the signal is recorded as a control signal on the lower edge of the tape 18.

The signal which has passed through the attenuator 25 is supplied through an amplifier 28 to a monostable multivibrator 29.

The switching and setting of the time constant of this monostable multivibrator 29 is carried out by the change-over of a switch 30. Resistors of different resistance values are connected between the monostable multivibrator 29 and the contacts of the switch 30. This monostable multivibrator 29 produces as output a pulse signal as indicated in Figure 2(B) which rises in response to a signal as indicated in Figure 2(A) from the amplifier 28 and falls with a time constant selected by the switch 30. This switch 30 is connected to the contact point R at the time of recording and at the time of normal reproduction. The above mentioned output pulse signal is formed into a sampling pulse signal by a sampling pulse forming circuit 31 and is thereafter supplied to a phase comparator (sampling circuit) 32.

The above mentioned rotary drum 16 is coaxially mounted on a vertical rotating shaft 33, which is driven by the motor 15 and rotates together with the rotary drum 16. A pair of magnets of opposite polarity are mounted on a rotating disc 34 fixed coaxially to the rotating shaft 33. Together with rotation of the rotary drum 16, pulses of positive polarity and negative polarity as indicated in Figure 2(C) are obtained alternately by pickup head 35 and are supplied to and trigger monostable multivibrators 36a and 36b. The outputs of the monostable multivibrators 36a and 36b of waveforms as indicated in Figures 2(D) and 2(E) are supplied to a flip-flop circuit 37. The resulting output of the flip-flop circuit 37 of the waveform indicated in Figure 2(F) is supplied to a trapezoid wave forming circuit 38 and formed into a trapezoid wave as indicated in Figure 2(G), which is then supplied to the phase comparator 32.

In the phase comparator 32, the sampling pulses from the sampling pulse forming circuit 31 samples the inclined part of the trapezoid wave. The resulting output signal of the phase comparator 32 is held by a sampling-hold circuit 39 and is supplied through a low-pass filter 40 for removing high frequency conponents and integrating and a driving amplifier 41 to the motor 15 thereby to control the rotation thereof. The rotational phase of the motor 15 is so controlled that the sampling position on the trapezoid wave in the phase comparator 32 will become a specific position, for example, the middle position of the inclined part of the trapezoidal wave.

In this connection, instead of controlling the rotation of the motor 15 by means of the phase comparator 32, the rotational phase of the motor 15 may be controlled by causing the motor 15 to rotate at a specific constant speed and controlling the electromagnetic braking of the rotation of the motor 15 by means of the output of the phase comparator 32. Still another alternative method which may be used is to control the rotation of the capstan 19 thereby to control the traveling phase of the tape 18 and to control the scanning phases of the heads 13a and 13b with respect to the tracks of the tape 18.

At the time of reproduction, the rotation of the motor 20 is controlled in response to a driving signal introduced through a terminal 42 in accordance with the mode of speedchange reproduction, and the tape 18 is caused to travel at a predetermined speed in accordance with the speed-change reproduction mode, as described hereinafter. In the case of still-picture reproduction, the motor 20 is not rotated, and the travel of the tape 18 is stopped. The video signals reproduced by the video heads 13a and 13b are passed through the recording and reproducing circuit 12 and led out through an output terminal 43.

At the time of reproduction, the moving contact of the switch 26 is switched to the contact point b, and the control signal reproduced from the control head 27 is supplied through the switch 26 and the amplifier 28 to the monostable multivibrator 29. The switch 30 is switched in accordance with the reproducing mode to one of its contact points PI through Pn respectively connected to resistors of different resistance values. The time constant of the monostable multivibrator 29 is selected by switching over of the switch 30 in accordance with the speed-change reproduction mode. By thus selecting this time constant, the fall position of the output pulse indicated in Figure 2(B) is variably set.

At the time of reproduction, also, the rotary drum 16 is rotated at a rotational speed of 30 Hz by the motor 15. The signal obtained by using the signal picked up by the pickup head 35 and the signal obtained by using the output signal of the monostable multivibrator 29 are phase compared, and, in response to the resulting output signal, the rotational phase of the motor 15 is controlled. This operation is similar to that at the time of recording.

Since the gaps of the video heads 13a and 13b respectively have mutually opposite azimuths, no signal is reproduced due to azimuth losses in the case where the video heads 13b and 13a respectively scan the tracks recorded by the video heads 13a and 13b (i.e., where so-called reverse tracking is carried out). Then, at the time of normal reproduction, the rotational phase of the motor 15 is so controlled that the sampling pulses will sample the middle part of the slope of the trapezoid wave formed in correspondence with pulses of positive polarity from the pickup head 35. In this case, the pulses of positive polarity from the pickup head 35 are so set that they are generated in coincidence with the rotational position of, for example, the head 13a. For this reason, in a normal reproduction mode, the rotational phases of the video heads 13a and 13b are so controlled that these heads will always scan (positive tracking) the tracks recorded by these heads 13a and 13b, and the above mentioned reverse tracking does not occur.

To prevent the occurrence of this reverse tracking, the circuit shown in Figure 3 may be used in the case where a control signal is not used. The reproduced frequency modulated video signal from the aforementioned terminal 43 is applied to a terminal 51 of the circuit shown in Figure 3 and subjected to envelope detection in an envelope detector 52. The resulting detected output is sampled in a sampling circuit 54 by pulses obtained from the signal of the pickup head 35 applied to a terminal 53. The resulting sampled output is led out through a terminal 55 and used for controlling the rotational phase of the motor 15.

In the system of the present invention, at the time of speed-change reproduction when reproduction is carried out at a tape speed (inclusive of zero, also) differing from the tape speed at the time of normal reproduction, the tape speed is so selected as to satisfy the following equation.

V = Vo (n + 2 where: V is the tape speed for speed-change reproduction mode; Vo is the tape speed for normal reproduction mode (and recording); and n is a positive integer.

The rotating speed of the heads 13a and 13b is always constant, i.e., 30 rps. in all reproduction mode. By thus selecting the tape speed so as to satisfy this equation, the minimum position of the reproduced signal level drop due to reproduction with the heads 13a and 13b deviating from their tracks (the distance from the tape edge, that is, the position on the reproduced picture screen) becomes always constant, as descirbed hereinafter.

In the case where the tape speed does not satisfy the above equation, the position of the noise bar arising in accompaniment with the minimal reproduced signal level is.not constant in the reproduced picture. Consequently, the quality of the entire reproduced picture is impaired by the noise, whereby a practically useful reproduced picture cannot be obtained.

Next, an example of fast (quick) motion reproduction wherein n is made equal to one (unity), and the positive-or-negative symbol within the parenthesis is made positive, that is, V = 3Vo, or triple-speed reproduction, will be described in conjunction with Figures 4A and 4B.

As indicated in Figure 4A, the video heads 13a and 13b have respective azimuth gaps 60a and 60b inclined by an azimuth angle a mutually in opposite directions relative to the direction perpendicular to the scanning direction. The tracks recorded and formed on the tape 18 by the video head 13a rotating in the arrow direction Y are designated by the characters tl, t3, t5, (wherein the subscripts of t are odd numbers), while the tracks recorded and formed by the video head 13b are designated by the characters t2, t4, t6, . (wherein the subscripts of t are even numbers). In this case, the tracks t1, t2, t3 .... are in contiguous contact without gaps therebetween, whereby the tape utilization efficiency is high.

Each track is recorded with a part of a video signal corresponding to substantially one field, and a vertical synchronizing signal is positioned near an end of the track.

Although not shown, an audio signal and a control signal are recorded respectively at the upper and lower lateral edges of the tape 18 along tracks in the longitudinal direction of the tape.

Here, it will be assumed that the head 13a starts to scan from a position, for example, where it straddles or spans over portions of the tracks t3 and t4. Then, since the tape 18 is traveling at a speed 3Vo which is three times the tape speed for recording (or normal reproducing), the head 13a scans the tape along a path indicated by broken line and terminates its scanning at a position where it straddles the tracks ts and t6.

Similarly, the head 13b scans from the position at which it straddles the tracks t6 and t, as indicated by broken lines and terminates scanning at the position where it straddles the tracks t8 and t9. Thereafter, the heads 13a and 13b trace other tracks in a similar manner.

Here, since the heads 13a and 13b have azimuths as described above, when they respectively scan the tracks recorded by the heads 13b and 13a, namely performs reverse tracking, no signal is reproduced because of azimuth loss. For this reason, in the case of the above mentioned example of scanning path, the head 13a reproduces a portion of the tracks t3 and tS as indicated by brokenline hatching. Similarly, the head 13b reproduces a portion of the tracks t6 and tx as indicated by the broken-line hatching. For this reason, the level of the signal reproduced by the heads 13a and 13b varies as indicated by broken line in Figure 4B.

In this case, the positions where the heads 13a and 13b respectively reproduce the entire widths of the tracks t4 and t7 are always at the same distances from their respective tape edges and are in the same positions in the longitudinal direction of the tape. Consequently, the minimum point of the level of the reproduced signal is at the same instant of time from the instant of start of scanning in the scanning periods of the heads 13a and 13b. At the minimum part of the reproduced signal level, the S/N ratio is very small, and a noise bar is produced in the reproduced picture. However, this noise bar appears always at the constant position in the reproduced picture.

Therefore, in accordance with the present invention, the tape speed is so selected as indicated by the equation set forth above that this noise bar will always be at the constant position in the reproduced picture, and, moreover, the rotational phases of the heads are so selected that this noise bar will be at a position in the picture screen where it will be inconspicuous or invisible as described hereinbelow.

In triple-speed fast-motion reproduction, the moving contact of the switch 30 is connected to the contact point Pl, and the time constant of the monostable multivibrator 29 is selected at a value conforming to this reproduction mode. Accordingly, the fall instant of its output pulse signal, as indicated in Figure 2(B), is extended to an instant corresponding to the pulses of negative polarity among the pulses derived from the pickup head 35 as indicated in Figure 2(C) in accordance with this time constant.

The control system of the motor 15 described in conjunction with Figure 1 controls the rotational phase of the motor 15 in a manner such that the pickup head 35 picks up a signal so that the central part of the trapezoid wave as indicated in Figure 2(G) will be sampled.by the sampling pulses obtained from the pulses indicated in Figure 2(B). Thus, at the time of this triple-speed fast-motion reproduction, rotational control is carried out intentionally so that the heads 13a and 13b will carry out reverse tracking.

Since the traveling speed of the tape 18 is three times the normal speed, the number of control signals reproduced through the control head 27 becomes three times, but since the time constant of the monostable multivibrator 29 is set at a large value as described above, this monostable multivibrator 29 responds to the reproduced control signals in a proportion of one in three and does not respond to the remaining two.

For this reason, the heads 13a and 13b do not scan in the manner indicated by the broken lines as described above but start their scanning from the reverse tracking positions as indicated by the bold full lines respectively from the positions of the tracks t4 and t7. Consequently, the head 13a traces parts of the tracks t4, t5, and t6, while the head 13b traces parts of the tracks t,, t8, and tg. Then, because of azimuth loss, the signals of the tracks 4 and t6 are not reproduced by the head 13a, and only the signal of the part indicated by full line hatching of the track t5 is reproduced.

Through the head 13b, the signals of the tracks t7 and t9 are not reproduced, and only the signal of the part indicated by full line hatching of the track t8 is reproduced.

For this reason, the levels of the signals reproduced by the heads 13a and 13b vary as indicated by full line Figures 4B. More specifically, the minimum points of the reproduced signal level coincide with the instants of scanning start and completion of the heads 13a and 13b. Then, since a vertical synchronizing signal is recorded at the end part of the track, the noise bar accompanying the above mentioned minimum points of the reproduced signal level falls within the vertical blanking period and does not appear in the reproduced picture.

Thus, the heads 13a and 13b carry out triple-speed fast-motion reproduction wherein the tracks t5 and ts are reproduced with respect to one field per three fields, and the reproduced picture moves with a speed which is three times that of normal reproduction. Moreover, no noise bar appears in the reproduced picture.

In the case where a vertical synchronizing signal is not reproduced, vertical synchroni zation of the picture may be achieved by using a separately generated vertical synchronizing signal. Furthermore in order to assure the positive reproduction of the vertical synchronizing signal, the time constant of the monostable multivibrator 29 may be so selected as to determine the rotational phases of the heads so that the above mentioned reproduced signal level point will be slightly offset from the position of the vertical synchronizing signal. In this case, a noise bar is slightly visible at the upper edge or lower edge of the reproduced picture but has almost no deleterious effect in actual practice.

Next, an example of reproduction under the condition of n = 2 and positive symbol within the parenthesis in the equation set forth hereinbefore, whereby V = 2Vo, that is, double-speed fast-motion reproduction, will be described in conjunction with Figures 5A and SB.

In this operation, the tape 18 is moved at the speed 2Vo, which is twice that for normal reproduction, and the moving contact of the switch 30 is connected to the contact point P2. As a result of the switching of the switch 30, the monostable multivibrator 29 is set at a time constant for doublespeed fast motion reproduction. As a consequence, similarly as in the preceding example, the monostable multivibrator 29 responds in a proportion of one per two to the control signals reproduced with double frequency through the control head 27, and its time constant is so set that the head 13a starts reverse tracking scanning.

The head 13a starts scanning from the track t4, for example, and ends its scanning at the track t5. The head 13b starts scanning from the track t6 and ends its scanning at the track t,. Thereafter, the heads 13a and 13b scan other tracks in a similar manner. In this case, the head 13a carries out reverse tracking with respect to the track t4 and normal tracking with respect to the track t5, while the head 13b carries out normal tracking with respect to the track t6 and reverse tracking with respect to the track t7.

Therefore, the heads 13a and 13b reproduce the tracks t5, t6, t9, t10, .. as indicated by hatching in Figure SA, and two fields per four fields are reproduced. Thus, doublespeed fast-motion reproduction is carried out at twice the speed of normal reproduction.

In this double-speed fast-motion reproduction, after the reproduction of two fields (i.e., one frame), one frame is skipped, and reproduction of the next one frame is carried out. For this reason, there is the advantage of less lowering of the vertical resolution than in the case of reproduction every one field.

As the head starts to scan from the starting end of the track t4 and continues to scan, the scanned area of the track t5 increases. Consequently, the level of the reproduced signal also increases, becoming a maximum at the lower end of the track t5.

On the other hand, as the head 13b starts to scan from the starting end of the track t6, the level of the reproduced signal is at its maximum value, and the scanned area of the track t6 decreases as the scanning proceeds. Accordingly, the reproduced signal level also decreases and becomes a minimum at the lower end of the track t6.

Accordingly, the levels of the signals .reproduced by the heads 13a and 13b becomes as indicated in Figure SB. The minimum point of the reproduced signal level occurs every two fields, that is, every one frame, Moreover, the accompanying noise bar is substantially within the vertical blanking period and is not conspicuous in the reproduced picture.

An example of reproduction under the condition of n = 4 and positive symbol within the parenthesis in the equation set forth hereinbefore, whereby V = (3/2)Vo, that is, 3/2-speed fast motion reproduction, will now be described in conjunction with Figures 6A and 6B.

In this case, the tape 18 is driven at a speed of (3/2)Vo, which is 1.5 times that in normal reproduction, and the moving contact of the switch 30 is connected to the contact point P3.

When the head 13a starts scanning from the track t4, for example, it completes scanning as it straddles the tracks t4 and tS.

Then the head 13b starts scanning as it straddles the tracks tS and t6 and ends scanning at the track t6. The head 13a starts scanning from the track t, and ends its scanning as it straddles the tracks t7 and t8.

The head 13b starts scanning as its straddles the tracks t8 and t9 and ends its scanning at the track t9. Thereafter, the (1/2)Vo, whereby 1/2-speed slow-motion reproduction is carried out, as described hereinbelow in conjunction with Figures 7.

The tape 18 is driven at a speed of (1/2)Vo, which is one half of the speed in ordinary reproduction, and the switch 30 is also switched accordingly. The time constant of the monostable multivibrator 29 is so selected that the head servo control is carried out in spite of halved frequency of the reproduced control signal.

The head 13a starts scanning from the track t6, for example, and ends its scanning as it straddles the tracks tS and 56. Then the head 13b starts scanning as it straddles the tracks t6 and t7 and ends its scanning at the track t6. The head 13a starts scanning from the track t7 and terminates its scanning as it straddles the tracks t7 and t6. The head 13b starts scanning as it straddles the tracks t7 ant t8 and ends its scanning at the track t7.

Then the head 13a starts scanning from the track t8 and ends its scanning as it straddles the tracks t7 and t8. Thereafter, similar scanning is carried out with respect to the other tracks.

Since the heads 13a and 13b accomplish normal tracking with respect to the tracks tS and t7 and the tracks t6 and t8, respectively, in this case, the parts indicated by hatching in Figure 7 are reproduced. Accordingly, the reproduced signal level of the reproducing heads 13a and 13b become similar to that indicated in Figure 6B, whereby the minimum level parts occur every four fields substantially within vertical blanking periods. Since the respective tracks are reproduced by two times scanning operations of each head, a slow-motion reproduced picture of one-half movement speed is obtained.

An example of reproduction under the condition of n = 3 and negative symbol within the parenthesis in the equation set forth hereinbefore, whereby V = (1/3)Vo, that is, 1/3-speed slow-motion reproduction, will now be described with reference to Figures 8A and 8B.

The tape 18 is driven at a speed of (1/3)Vo, which is 1/3 of that for normal reproduction. When the head 13a starts its scanning from track t6, for example, it ends its scanning as it straddles the tracks t5 and t6. The head 13b starts its scanning as it straddles the tracks t6 and t7 and, after scanning over the entire track t6, ends its scanning as it straddles the tracks t6 and tS.

Then the head 13a starts its scanning as its straddles the tracks t6 and t7 and ends its scanning at the track t6. Thereafter, similar scanning is carried out with respect to the other tracks.

Accordingly, the reproduced signal level of the heads 13a and 13b becomes as indicated in Figures 8B, and the minimum reproduced signal level point occurs every three fields substantially within the vertical blanking period.

In the case where, in the equation set forth hereinbefore, n is made to equal 2, and the symbol within the parenthesis is caused to be negative, the tape velocity V becomes zero, and still picture reproduction is carried out with the tape in stopped state.

In Figure 9, when the head 13a starts to scan from the track t6, for example, it ends its scanning at the track tS. Since the tape 18 is stopped, the head 13b also starts scanning from the track t6 and ends its scanning at the track t5. Thereafter, the above described scanning operation is repeated. Since the tracks 13a and 13b have a normal tracking relationship to the tracks tS and t6, respectively, the parts indicated by hatching are reproduced. Accordingly, the reproduced signal level of the heads 13a and 13b becomes as indicated in Figure SB.

In this case, since the tape travel is stopped, no control signal is reproduced.

For this reason, the rotational phases of the heads 13a and 13b are not controlled as in the case of the above described reproduction modes, the exact track end position on the tape from which scanning will start cannot be readily determined. In the case where each of the heads starts its scanning from the position where it straddles two tracks, a noise bar appears at a conspicuous position in the reproduced picture. In this case, by manually shifting the tape through a very small distance thereby to cause each head to start its scanning from just the starting end of a track, the noise bar is caused to be hidden within the vertical blanking periods.

Since the reproduced video signal is almost nonexistent in a minimum level point of the reproduced signal, the reproduced horizontal synchronizing signal is also almost nonexistent. Accordingly, it is also possible by utilizing this phenomenon to cause the noise bar to be automatically within the vertical blanking period. In this case, by a known sampling technique, the presence or absence of a reproduced horizontal synchronizing signal or whether or not the level is below a specific level is detected by a method such as sampling the reproduced horizontal synchronizing signal and the output signal of a sawtooth wave oscillator or slicing the outputs obtained by gating the two signals at a specific level. The resulting detection signal may be used to trigger a monostable multivibrator, the resulting output of which is used to rotate the capstan motor 20 intermittently during very small periods to cause the tape 18 to shift intermittently through minute distances, whereby each head starts its scanning at just the starting end of a track as indicated in Figure 9.

In the case where, in the equation set forth hereinbefore, n is made to equal one (unity), and the symbol within the parenthesis is caused to be negative, the tape velocity V becomes -Vo, and the direction of travel of the tape will become reversed.

These are conditions for a reverse-motion reproduction.

In this case, the tape 18 is driven in reverse travel in the arrow direction X, opposite to the aforementioned direction X, at a speed of Vo as indicated in Figure 10.

The switch 30 also is so switched as to cause the time constant of the monostable multivibrator 29 to be of a value suitable for reverse-motion reproduction.

When the head 13a starts to scan from the track t8, for example, it scans the track t7 and further ends its scanning at the track t6.

The head 13b starts to scan the track t7 and, scanning the track t6, ends its scanning at the track tS. Similarly, the head 13a scans from the track t6 to the track t4, while the head 13b scans from the track t5 to the track t3. Thereafter, scanning is similarly carried out with respect to the other tracks.

In this case, since the heads 13a and 13b have a relationship wherein they carry out normal tracking with respect to the tracks t7, tS, t3, and the tracks t6, t4 t4,....., respectively, the head 13a reproduces the tracks t7, tS , and the head 13b reproduces the tracks t6, t4 .... as indicated by the hatching in Figure 10. Accordingly, the reproduced signal level of the heads 13a and 13b becomes similar to that indicated by full line in Figure 4B.

In this case, since the reproduction is carried out in a track sequence which is the reverse of the recording track sequence of tracks t7, t6, tS, t4 , reverse-motion reproduction, wherein the reproduced picture becomes reversed in time sequence in movement relative to that of a normal reproduction, is obtained.

In the case where, as a result of the traveling of the tape 18 in the reverse direction, the polarity of the reproduced control signal becomes reversed, an inverter may be provided to invert the polarity.

While, in each of the above described embodiments of the invention, the rotation al phases of the rotating heads 13a and 13b are so controlled as to cause the noise bar due to the minimum reproduced level to be substantially within the vertical blanking periods, the rotation of the motor 20 may be controlled thereby to control the traveling phase of the tape 18.

The video signals reproduceable by the system of the present invention are not limited to color video signals but may be monochrome video signals. The only re quirement is that these signals have been recorded by heads having different azimuth angles on mutually neighboring tracks.

Further, this invention is not limited to these embodiments but various variations and modifications may be made without departing from the scope of the invention.

WHAT WE CLAIM IS: 1. A video signal speed-change reproducing system comprising: a tape on which a video signal has been recorded with tracks disposed contiguously and obliquely relative to the tape longitudinal direction, said tracks being recorded and formed by a plurality of rotating heads having gaps at mutually different azimuth angles; means for causing said tape to travel at a speed V represented by the equation n+2 V V (n + 2 ) wherein Vo is the tape speed for normal reproduction (and recording), and n is a positive integer, and for causing the tape to be stopped during still picture reproduction; and reproducing means having a plurality of rotating heads having gaps at mutually different azimuth angles which are the same as said azimuth angles of the recording heads and arranged to successively scan said tracks of the tape thereby to reproduce said recorded video signal from the tracks formed by the recording head having the gap at one of the different azimuth angles by means of the rotating head having the gap at the one azimuth angle and from the tracks formed by the recording head having the gap at the other azimuth angle by means of the rotating head having the gap at the other azimuth angle.

2. A video signal speed-change reproducing system as claimed in Claim 1 in which said reproducing means is arranged to carry out reproduction in a manner such that each time instant at which the level of the reproduced signal becomes of minimum value is within or in the vicinity of a vertical blanking period.

3. A video signal speed-change reproducing system as claimed in Claim 1 in which each of the tracks is recorded near an end part thereof with a vertical synchronizing signal of the video signal, and which further has control means for so controlling the rotational phases of said rotating heads of the reproducing means that an area in which said rotating heads scan the tracks recorded with the same azimuth angle as the azimuth angle of said rotating heads of the reproducing means, will become minimal at the starting end or the terminal end of tracks scanned by said rotating heads.

4. A video signal speed-change reproducing system as claimed in Claim 1 in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Figure 9. In the case where, in the equation set forth hereinbefore, n is made to equal one (unity), and the symbol within the parenthesis is caused to be negative, the tape velocity V becomes -Vo, and the direction of travel of the tape will become reversed. These are conditions for a reverse-motion reproduction. In this case, the tape 18 is driven in reverse travel in the arrow direction X, opposite to the aforementioned direction X, at a speed of Vo as indicated in Figure 10. The switch 30 also is so switched as to cause the time constant of the monostable multivibrator 29 to be of a value suitable for reverse-motion reproduction. When the head 13a starts to scan from the track t8, for example, it scans the track t7 and further ends its scanning at the track t6. The head 13b starts to scan the track t7 and, scanning the track t6, ends its scanning at the track tS. Similarly, the head 13a scans from the track t6 to the track t4, while the head 13b scans from the track t5 to the track t3. Thereafter, scanning is similarly carried out with respect to the other tracks. In this case, since the heads 13a and 13b have a relationship wherein they carry out normal tracking with respect to the tracks t7, tS, t3, and the tracks t6, t4 t4,....., respectively, the head 13a reproduces the tracks t7, tS , and the head 13b reproduces the tracks t6, t4 .... as indicated by the hatching in Figure 10. Accordingly, the reproduced signal level of the heads 13a and 13b becomes similar to that indicated by full line in Figure 4B. In this case, since the reproduction is carried out in a track sequence which is the reverse of the recording track sequence of tracks t7, t6, tS, t4 , reverse-motion reproduction, wherein the reproduced picture becomes reversed in time sequence in movement relative to that of a normal reproduction, is obtained. In the case where, as a result of the traveling of the tape 18 in the reverse direction, the polarity of the reproduced control signal becomes reversed, an inverter may be provided to invert the polarity. While, in each of the above described embodiments of the invention, the rotation al phases of the rotating heads 13a and 13b are so controlled as to cause the noise bar due to the minimum reproduced level to be substantially within the vertical blanking periods, the rotation of the motor 20 may be controlled thereby to control the traveling phase of the tape 18. The video signals reproduceable by the system of the present invention are not limited to color video signals but may be monochrome video signals. The only re quirement is that these signals have been recorded by heads having different azimuth angles on mutually neighboring tracks. Further, this invention is not limited to these embodiments but various variations and modifications may be made without departing from the scope of the invention. WHAT WE CLAIM IS:

1. A video signal speed-change reproducing system comprising: a tape on which a video signal has been recorded with tracks disposed contiguously and obliquely relative to the tape longitudinal direction, said tracks being recorded and formed by a plurality of rotating heads having gaps at mutually different azimuth angles; means for causing said tape to travel at a speed V represented by the equation n+2 V V (n + 2 ) wherein Vo is the tape speed for normal reproduction (and recording), and n is a positive integer, and for causing the tape to be stopped during still picture reproduction; and reproducing means having a plurality of rotating heads having gaps at mutually different azimuth angles which are the same as said azimuth angles of the recording heads and arranged to successively scan said tracks of the tape thereby to reproduce said recorded video signal from the tracks formed by the recording head having the gap at one of the different azimuth angles by means of the rotating head having the gap at the one azimuth angle and from the tracks formed by the recording head having the gap at the other azimuth angle by means of the rotating head having the gap at the other azimuth angle.

4. A video signal speed-change reproducing system as claimed in Claim 1 in

which the tape bears a control signal recorded thereon, and which further comprises: means for reproducing said control signal from the tape; a monostable multivibrator triggered by the control signal thus reproduced; means for switching and setting the time constant of said monostable multivibrator in accordance with a selected speed-change reproduction mode; means for detecting the rotational phases of the rotating heads; means for phase comparing the resulting rotational phase detection signals and the resulting output signal of the monostable multivibrator; and means for controlling the rotational phases of said rotating heads or the traveling phase of the tape with the resulting output signal of said phase comparing means so that the time instant, at which the level of the reproduced signal will be a minimum, will be within or in the vicinity of the vertical blanking period of the video signal.

5. A video signal speed-change reproducing system comprising: a tape on which a video signal has been recorded with tracks disposed obliquely to the tape longitudinal direction in mutually contiguous contact with substantially no gaps therebetween, said tracks being alternately recorded and formed by a pair of rotating heads having gaps at mutually different azimuth angles, a vertical synchronizing signal of the video signal being recorded on each of said tracks near an end thereof; means for causing the tape to travel at a speed V represented by the equation V = Vo ( n )' wherein Vo is the tape speed for normal reproduction (and recording), and n is a positive integer, and for causing the tape to be stopped during still picture reproduction; means for successively scanning said tracks of the tape by means of said rotating heads thereby to reproduce the recorded video signal; and means for controlling the rotational phases of said rotating heads so that an area, in which each of said rotating heads scans the tracks recorded by itself, will become minimal at the starting end or the terminal end of the tracks scanned by the rotating heads.

6. A video signal speed-change reproducing system substantially as described with reference to the accompanying drawings.