GB2133604A - Multiplex recording and playback system for VTR - Google Patents

Abstract

A multiplex recording and playback system records an audio signal into and plays it back from a track which also stores a video signal. A rotary member 10, around which a magnetic tape is wound, carries two video signal read-and-write rotary heads H1, H2 and a single audio signal read-and-write rotary head HA exclusively allocated to the audio signal and located ahead of one of the video heads by a predetermined angular distance. The audio head, which has an azimuth angle substantially larger than those of the video heads, deals at each scan with an even number of frequency-division- multiplexed audio signals relating to two adjacent video tracks, of which those relating to one track have been delayed by one track-scan period. <IMAGE>

Description

SPECIFICATION Multiplex recording system and multiplex recording and playback system for VTR Background of the Invention The present invention relates to a multiplex recording system and multiplex recording and playback system for VTR and, more particularly, to a system for recording an audio signal into and playing it back from a track common to a video signal.

As well known in the art, in a helical scan magnetic recording and playback apparatus (VTR), a plurality of rotary heads, such as two, are mounted on a drum or like rotatable member atan equal angular distance. A magnetic tape is would around the rotary member over an angular range which may be a little over 180 degrees, for example. The rotary heads on the rotatable member are adapted to write video signals in the magnetic tape. Meanwhile, a stationary head is located in the path of travel of the magnetic tape so as to write audio signals therein. During playback, the rotary heads read the video signals and the stationary head, the audio signals.

A current trend in the art of video tape recording is to a longer record and playback time and, therefore, to a lower running speed of a magnetic tape. At the same time, there is an increasing demand for higher quality in the playback of audio signals. Because the relative speed between the running tape and the stationary head for writing and reading audio signals is low, there arises a dilemmatic situation that a decrease in the running speed of the tape significantly deteriorates the frequency characteristic of audio signals, compared to that of video signals which are written and read by the rotary heads, preventing audio signals from being reproduced with a desirable quality.

In light of this, there has been proposed a system which superposes an audio signal on a video signal after converting it into a predetermined mode, and records the superposed signals in a magnetictape by means of a video signal read and write head and reads them out of the magnetic tape. In accordance with such a system, because a rotary head writes and reads an audio signal in and out of a magnetic tape which moves at a high speed relative to the head, the recording and playback quality is far higher than the system which writes and reads an audio signal by means of a stationary head without slowing down the movement of the tape.

In the proposed recording and playback system described above, an audio signal is subjected to at least frequency modulation and then superposed on a video signal which may be made up of a frequency modulated luminance signal and a low range carrier color signal, the superposed signals being written and read by a common rotary head. This brings about a problem that beat occurs between the carrier frequencies to develop interference (more') in a reproduced picture.

Summary of the Invention It is therefore an object of the present invention to provide a multiplex recording and playback system forVTR which solves the problem discussed above by employing a rotary head exclusively allocated to audio signals.

It is another object of the present invention to provide a generally improved multiplex recording and playback system for VTR.

A multiplex recording system for a video tape recorder of the present invention comprises a rotary member around which a magnetic recording medium is wound over a predetermined angular range, at least two video signal recording rotary heads mounted on the rotary member at a predetermined spacing from each other, the rotary head having azimuth angles which are different from each other and recording a video signal on the magnetic recording medium, a single audio signal recording rotatable head mounted on the rotary member in a position ahead of one of the two video signal recording rotary heads by a predetermined angle with respect to an intended direction of rotation of the rotary member, the audio signal recording rotary head having an azimuth angle which differs from the azimuth angles of the video signal recording rotary heads, and record processing circuit for producing from an audio signal fed thereto, a first frequency modulated audio signal, and a second frequency modulated audio signal which is delayed by one track scan period with respect to said first frequency modulated audio signal and for frequency division multiplexing the first and second frequency-modulated audio signals, supplying the multiplexed signal to the audio signal recording rotary head thereby said first and second frequency modulated audio signals are segmented to a time length of one track scan period and are recorded on the magnetic recording medium at every other track scan period forming tracks with one track space between adjacent tracks of the formed tracks, while the video signal recording rotary heads form video tracks of the video signal over the formed audio tracks.

In accordance with the present invention, a multiplex recording and playback system records an audio signal into and plays it back from a track which has stored a video signal. A rotary member, around which a magnetic tape is wound, carries therewith a plurality of video signal read and write rotary heads and a single audio signal read and write rotary head exclusively allocated to the audio signal and located ahead one of the video signal read and write heads by a predetermined angular distance. The audio signal read and write head has an azimuth angle which is sufficiently larger than those of the video signal read and write heads.

The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.

Brief Description of the Drawings Figures 1 and2 are plan and side elevational views respectively, which show a head arrangement and the like in accordance with the present invention; Figure 3 is a block diagram of a recording system embodying the present invention; Figure 4 is a plot showing exemplary frequency spectra ofsignalswhich may be recorded and played back by the system of the presnt invention; Figure 5 is a view of an exemplary tape pattern which may be recorded and played back by the system of the present invention; Figure 6 is a block diagram of essential part of another embodiment of the recording system; Figure 7 is a block diagram of an example of part of the construction shown in Figure 6; Figure 8 is a block diagram of a playback system in accordance with the present invention; and Figure 9 is a block diagram of another embodiment of the playback system.

Description of the Preferred Embodiments While the multiplex recording system and multiplex recording and playback system for VTR of the present invention is susceptible of numerous physical embodiments, depending upon the environment and requirements of use, substantial numbers of the herein shown and described embodiments have been made, tested and used, and all have performed in an eminently satisfactory manner.

Referring to Figures 1 and 2, there is shown an arrangement of various heads and the like in accordance with a preferred embodiment of the present invention. A rotary drum 10, which is an exemplary rotatable member, rigidly carries on its peripheral surface a pair of video signal read and write heads Ht and H2. These heads H1 and H2 face each other at an angular spacing of 180 degrees along the circumference ofthe rotary drum 10. The drum 10 also carries therewith an audio signal read and write head HA ahead the video signal read and write head H1 by an angle 0 with respect to an intended direction of rotation of the drum 10. All the heads H1, H2 and HA are rotatable integrally with the drum 10 and, for this reason, they will be referred to as "rotary" heads hereinafter.As shown in Figure 2, the heads H1 and H2 are positioned at a same level on the drum 10 and above the head HA at a distance d. The drum 10 is disposed above a stationary drum 12 in such a mannew that its bottom faces the top of the drum 12 at a small spacing. A magnetic tape 14 is guided by guide poles 16a and 16bto extend around the rotary drum 10 over an angle somewhat larger than 180 degrees, while being inclined relative to the drum 10. During a recording or playback operation, the drum 10 is driven counterclockwise about its axis as viewed in Figure 1, and the tape 14 in a direction indicated by an arrow x.

The rotary heads H1 and H2 differ in azimuth angle from each other. The rotary head HA has an azimuth angle which is sufficiently larger than those of the rotary heads H1 and H2. As will be described, a video track formed by the head H2 and an audio track formed by the head HA during a recording operation are located in a same position on the tape 14. Therefore, it is preferable that the difference in azimuth angle between the heads H2 and HA be largerthan that between the heads H1 and HA. The azimuth angle of the head HA has to be different from those of the heads H1 and H2 in order that the audio signal may be reproduced without interference with the video signal; it should preferably be sufficiently larger than those of the heads H1 and H2 to allow a minimum of interference to occur during playback.In this particular embodiment, the azimuth angle is selected to be -6 degrees forthe head H1, +6 degrees for the head Hz, and -30 degrees for the head HA.

In order to locate the video track which the head H2 forms and the audio track which the head Hun forms in a same position, as previously described, the head HA is positioned ahead the head Hr by the angle 0 and below the head H1 at the distanced. In the illustrated embodiment, the drum 10 has a diameter of 62 mil- limeters, the angle 0 is 55 degrees, and the distanced is 13 microns. Due to the vertical distance d, the head HA start forming an audio track at a position which is deviated about 18 microns from the position where the head H2 starts fo rmi ng a video track. However, the deviation is microscopic and negligible in practice.

Referring to Figure 3, a signal processing system associated with the arrangement of Figure 1 and 2 is shown. An input terminal 18 receives a left channel audio signal, an input terminal 20 a right channel audio signal, and an input terminal 22 a standard color video signal, by way of example. The left chan nel audio signal is fed from the input terminal 18 to a 1-field delay circuit 24to be thereby delayed by a time equal to one field period of a standard color video signal to be recorded (e.g. about 1/60 second). The output of the field delay circuit 24 is applied to a frequency modulator 26. At the same time, the left channel audio signal is fed directly to a frequency modulator 28 without any delay.The right channel signal, on the other hand, is fed from the inputtermi nal 20 to a frequency modulator 32 via a field delay circuit 30 and directly to a frequency modulator 34.

The 1 field delay circuits 24 and 30 have a common construction and individually comprise charge transfer devices such as bucket brigate devices (BBD) or charge coupled devices (CCD). The frequency mod ulator 26 subjects a carrier frequency fi (e.g. 1.1 MHz) to frequency modulation (FM) by the delayed left channel audio signal, thereby producing a first FM audio signal. The frequency modulator 28 frequency-modulates a carrier frequency f4 (e.g. 1.85 MHz) by the nondelayed left channel audio signal, thereby producing a second FM audio signal.Likewise, thefrequency modulator 32 develops a third FM audio signal by frequency-modulating a carrier fre quencyfi(e.g. MHz) bythedelayed right channel audio signal, and the frequency modulator34afourth FM audio signal by modulating a carrier frequency f3 (e.g. MHz) by the nondelayed right channel audio signal.

All the first to fourth FM audio signals have a com mon maximum frequency deviation such as +100 kHZ and are delivered to a mixer 36 to be frequency division multiplexed. The multiplex output of the mixer 36 is applied to a gate 38 which repeatedly opens and closes at every one field period, so that the mixer output is sent out at every interval of one field period. The output of the gate 38 is routed to the signal audio single read and write rotary head Hn via a rotary transformer 40.

In the manner described,the audio signal in each of the two channels is converted into first and second (or third and fourth) FM audio signals by frequency modulating different carrier frequencies fi and f4 (orf2 and f3) by afirst audio signal appearing at every interval of one field period and a second audio signal appearing at every another interval of one field period. The two FM audio signals are subjected to frequency-division multiplexing in the same one field period, the multiplex signal being applied to the rotary head HA at every interval of one field period.

Meanwhile, the standard color video signal arrived at the input terminal 22 is delivered to a luminance signal write system 42 and a carrier color signal write system 44, thereby being separated into a luminance signal and a carrier color signal. The luminance signal write system 42 produces an FM luminance signal having a carrier frequency deviation which provides, for example, a sync chip level of 3.4 MHz and a white peak of 4.4 MHz. The carrier color signal write system 44 produces a low range carrier color signal which has undergone frequency conversion to a band lower than that of the FM luminance signal, and has been phase-shifted by a known manner to overcome crosstalk. The FM luminance signal and the low range carrier color signal, whose color subcarrierfrequency may be 629 kHz, are fed to a mixer 46 for frequency division multiplex.The output of the mixer 46 is routed to the rotary heads H1 and H2 via rotary transformers 48 and 50 associated therewith.

The various signals written into or read out of the magnetic tape 14 in accordance with the present invention have frequency spectra such as those shown in Figure 4. In Figure 4, FM-Y is the frequency spectrum ofthe FM luminance signal outputfromthe luminance signal write system 42, and C the fre quencyspectrum of the low range carrier color signal output from the carrier color signal write circuit 44.

Further, A1, A2, A3 and A4 are the frequency spectra of the first, second, third and fourth FM audio signals respectively. As shown in Figure 4, the first to fourth FM audio signals are distributed in a band adjacent to the lower frequency limit of the FM luminance signal and are written in the tape at the saturation level.

Hereinafter will be described a tape pattern in accordance with the present invention. Assume that the rotary head HA has started writing the frequency division multiplex signal of the first to fourth FM audio signals on the magnetictape 14. Then, an audio track begins to form itself in an inclined position relative to the lengthwise direction of the tape 14. At a timelaterthanthatbya period of time corresponding to the angular movement ofthe drum 10 by the angle 0, the head H1 starts forming a video track which is inclined a same angle asthe audio track and started at a position upstream ofthe audio track with respect to the tape. The video track stores the frequency division multiplex signal made up of the FM luminance signal and low range carrier color signal.In this manner, the rotary heads HA and H. respectively form the audio track and video track at the same time with a predetermined time gap. As the rotary head H1 approaches the guide pole 16b shown in Figure 1, it completes writing data into one audio track one audio track has been completed the predetermined time before the audio track). Then, the rotary head H2 starts forming a video track on the tape 14.

The position where the head H2 is to form a video track is dislocated by one track pitch to the down stream side on the tape from the video track formed by the rotary head H1 and, in this position, one audio track has already been formed. Therefore, the head H2 records a video track on the audio track previously formed on the tape. The underlying audio track has stored the first to fourth FM audio signals of low frequencies as indicated by A1 -A4 in Figure 4. Due to the relatively long record wavelength, the FM audio signals have been written at the saturation level deep into the magnetic layer.

In contrast, among the video signals in the video track overlying the audio track, the FM luminance signal is written mainly into a portion of the magnetic layer adjacent to the surface ofthetape 14, since it has a high frequency as indicated by FM-Y in Figure 4.

Therefore, the FM audio signal ishardlyerased bythe FM luminance signal. The low range carrier color signal, on the other hand, has a low frequency as indicated by C in Figure 4 which reaches a deep portion of the magnetic layer when written into the tape 1 4tending to erase the previously recorded FM audio signal. In accordance with the present invention, however, while the FM audio signal has been recorded at the saturation level as already mentioned, the overlying low range carrier color signal is recorded at a level lower than the saturation level.

This maintains the FM audio signal at the reproducible level allowing only a negligible degree of erasure of the FM audio signal to be caused by the carrier color signal.

Therefore, even if the video track is superposed on the audio track by the rotary head H2, the FM audio signal remains in the magnetic layer at the reproducible level while the low range carrier color signal and FM luminance signal are written into the same position on the tape 14.

Just before the head H2 completes one video track on the tape 14, the head HA starts forming another audio track in a position two track pitches remote from the immediately preceding audio track. In this manner, audio tracks recorded with FM audio signals by the head HA are formed at a two-track pitch on the tape 14, and video tracks recorded with low range carriercolorsignals and FM luminance signals by the heads H1 and H2 at a one-track pitch. The head H2 superposes a video track on the previously recorded audiotrack. In thistrack forming process, the four FM audio signals are segmented to one track scan period of the head HA as recorded audio signals, discarding approximately one track scan period of the four FM audio signals while the head HA is not contacting the tape 14. This means that writing of the FM audio signals on the tape 14 occurs every other track scan period in terms of time continuity.

Referring to Figure 5, an exemplary tape pattern achievable with the system of the present invention is shown. The tape 14 carried thereon various tracks which are individually inclined relative to the lengthwise direction of the tape 14. Among the various tracks, white ones represent video tracks formed bythe head H. and hatched ones represent superposition of the video tracks formed by the head H2 on the audio tracks. Each track, whether it be an audio track or a video track, is assumed to have a width TW and neighbor the others at a track pitch TP. Because no guard band is formed between adjacent tracks in this example, the track width TW is identical with the track pitch TP. Each track has a capacity to store one field of video signal. Also shown in Figure 5 are a control signal write track Tc and an audio signal write track TA.Read and write systems associated with the tracks Tc and TA are not directly relevanttothe purportofthe present invention and, therefore, description thereof will be omitted. The track Tun stores audio information which was directly written thereinto by a stationary head without frequency modulation. Therefore, when the tape 14 is played back by a conventional VTR, the audio signal will be picked up from the track TA.

Referring to Figures 6 and 7, a second embodiment of the recording system in accordance with the present invention is shown. In Figure 6, the same or simi larstructural elements as those shown in Figure 3 are designated by the same reference numerals. The video signal write system in this embodiment is common to that of Figure 3 and, therefore, omitted for simplicity. As shown, the second FM audio signal output from the frequency modulator 28 is applied to a delay and frequency converter 52 and to a mixer54.

Thefourth FM audio signal outputfrom the frequency converter 34 is applied to a delay and frequency converter 56 and to a mixer 54.

The delay and frequency converters 52 and 56 are constructed in the same manner and as shown in Figure 7, for example. In Figure 7,the second orfourth FM audio signal arrived at a terminal 58 is written into a digital memory 60. An oscillator 62 oscillates a rectangular wave whose frequency is, for example, 2.95 MHz and delivers it to a counter 64. The counter 64 is constructed to be reset by a drum pulse which is generated by known means with a period equal to the period of one rotation of the drum 10 and synchron ized with the rotation phase, the drum pulse being applied to an input terminal 66. Also, the counter 64 counts rectangular waves fed thereto from the oscil lator 62 and supplies a count output thereof to the digital memory 60 as an address signal.

With the above arrangement, the digital memory 60 supplies the following band pass filter 68 with a digital FM audio signal which has been delayed by the time period for which one track of video information is completed, i.e. one field period in this embodiment.

The band pass filter 68 produces a sinusoidal wave having a same band as the FM audio signal applied to the input terminal 58. The output of the band pass filter 68 is delivered to a frequency converter 70 which is supplied with a sinusoidal wave of, for example, 2.95 MHz from an oscillator 72. The frequency conver- ter 70 subjects the incoming FM audio signal fre quency and the sinusoidal frequency to frequency conversion. The output of the frequency converter70 is sent out to an output terminal 76 via a band pass filter 74 having such a frequency characteristic as to filter a difference component between the two fre quencies.

Therefore, when the second FM audio signal hav ing a frequency of 1.85 t 100 kHz is applied to the input terminal 58, the first FM audio signal whose frequency is 1.1 MHz 1 100 kHz appears at the output terminal 76; when the fourth FM audio signal with the frequency of 1.6 MHz 1 100 is applied to the intput terminal 58, the third FM audio signal with the frequency of 1.35 MHz 1 100 kHz appears at the output terminal 76. The first and third FM audio signals output from the delay and frequency converters 52 and 56 are frequency-division multiplexed with the second and fourth FM audio signals bythe mixer54. The output of the mixer 54 is routed to the rotary head HA via the rotary transformer 40.As in the first embodiment, a gate (not shown) supplies the head HA with the first to fourth FM audio signals intermittently at every interval of one field.

In Figure 7, the delay and frequency converters 52 and 56 may share the oscillators 62 and 72 and counter 64 (provided f1 + f4 = f2 + f3). While the oscillators 62 and 72 are originally independent of each other, they may comprise a single oscillator since their oscillation frequencies are equal to each other. If desired, the delay and frequency converters 52 and 56 may be shared by the recording system and the playback system, as shown in the recording system of Figure 9. In accordance with this particular embodiment, resetting the counter 64 by the drum pulses provides a substantially accurate one field of delay time.

Referring to Figure 8, a playback system in accordance with the present invention is shown. In Figure 8, the same or similar structural elements as those of Figure 3 are designated by the same reference numerals. The rotary head HA in Figure 8 is adapted to scan the hatched tracks shown in Figure 5 in which audio tracks and video tracks are laid one upon the other (referred to as "superposed record tracks" hereinafter for convenience). As previously stated, each audio track is formed by the rotary head HA whose azimuth angle is -30 degrees, for example, and each video track superposed on the audio track by the head H2 whose azimuth angle is +6 degrees, for example. Hence, while scanning the superposed record track mentioned above, the head HA will rep reduceonlythefirsttofourth FM audio signals due to the azimuth loss effect.

The video tracks located at either side of a superposed record track on the tape 14 have been formed by the head H. have an azimuth angle of -6 degrees, for example. With respect to the audio track, therefore, a guard band corresponding to the width TW of the essentially single video track is formed which prevents the head HA from reproducing previously recorded FM audio signals in adjacent superposed record tracks as cross-talk while scanning a specific superposed record track.

The first to fourth FM audio signals thus reproduced from a superposed record track scanned by the head Hnare respectively supplied to band pass filters 80, 82, 84 and 86 via the rotary transformer 40 and a preamplifier78. Because the centerfrequencies of the band pass filters 80,82, 84 and 86 are predetermined to be fi, ~4, f2 and f3 respectively, they pick up the first to fourth FM audio signals by frequency selection and apply them to their associated FM demodulators 88, 90, 92 and 94.

The FM demodulator 88 frequency-demodulates the first FM audio signal into the one-field delayed left channel audio signal and applies itto aterminala of a switch 96. The FM demodulator 92 reproduces the one-field delayed right channel audio signal. Simul taneously,the FM demodulator 90 reproducesthe left channel audio signal and applies it to a Field delay circuit 100, which comprises a charge transfer device or the like. The FM demodulator 94 reproduces the right channel audio signal. Which is then applied to a field delay circuit 102. The outputs of the i-field delay circuits 100 and 102 are fed to terminalsh of switches 96 and 98 respectively.

Each of the switches 96 and 98 and a switch 104, which will be described, is constructed to alternately connect to the terminals a and b at every one track scan period (one field period in this embodiment) and in response to the drum pulses applied to an input terminal 106. For one field period for which the head HA scans a superposed record track, the switches are commonly connected to the terminals a as shown in Figure 8. In the position shown in Figure 8, the switch 98 delivers to an outputterminal 108 the output signal of the FM demodulator 88, that is, of the two kinds of left channel audio signals stored in the superposed record track, one which precedes the other by one field period. Likewise, the switch 98 delivers to an output terminal 110 one of the two kinds of right channel audio signals which precedes the other by one field period.

While the head Hn scans a superposed record track, the head H1 scans a video track indicated by a blank in Figure 5 at a predetermined time of delay. The video signal in the video track scanned by the head H1 is delivered to a brightness signal read system 114 and a carrier color signal read system 116 via the rotary transformer 48, a preamplifier 112, and the switch 104 which is in contact with a terminal a. The brightness signal read system 114 filters the reproduced FM brightness signal, demodulates it into a reproduced brightness signal in the original band, and then supplies it to a mixer 118.The carrier color signal read system 116 filters the reproduced low range carrier color signal backto restore the original band and, by use of a comb filter, removes low range carrier color signals read from adjacent superposed record tracks as cross-talk. In this manner, the carrier color signal read system 116 picks up only the carrier color signal read out of the scanned track and supplies it to the mixer 118. Mixingthetwo inputsignalsthe mixer 118 delivers a reproduced standard color video signal to an output terminal 120.

As the heads HA and H1 fully scan the tracks, the switches 96,98 and 104 are individually actuated into contact with the other terminals 6 while the head H2 starts scanning a superposed record track. Due to the previously mentioned azimuth loss effect, the head H2 reproduces onlythe signal recorded in thevideo track in the superposed record track, without reproducing the FM audio signal in the audio track. That is, the head H2 reproduces out of the superposed record track the frequency division multiplex signal made up of a low range carrier color signal and FM luminance signal. The reproduced multiplex signal is routed to luminance playback system 114 and a carrier color signal playback system 1 via a preamplifier 122 and the switch 104 which is in contact with the terminal b this time.Because the playback systems 114 and 116 function in the manner previously discussed, the mixer 118 applies to an output terminal 120 one field of video signal read out of the superposed record track as a reproduced standard color video signal. As described above, in accordance with this embodiment, the heads H2 and HA having different azimuth angles record different kinds of information one upon the other and sequentially read them out with azimuth angles particular thereto. This hardly entails mutual interference betwen an FM audio signal and a low range carrier color signal and FM luminance signal which would occur due to beat when a single rotary head is employed to write and read them at the same time. The result is quality playback of color video signals and audio signal.

Meanwhile, while the head H2 is scanning a superposed record track, among the two kinds of reproduced FM audio signals for each channel read out by the head HA one field before by scanning the same superposed record track, the left channel audio signal after the one field period is produced from the field delay circuit 100, and the right channel audio signal after the one field period from the 1 field delay circuit 102. These audio signals are applied to the output terminals 108 and 110 via the switches 96 and 98 respectively. As a result, the right and left channel reproduced audio signals appear at the output terminals 108 and 110 constantly without interruption and in the correct order.

In the embodiment described above, both the switches 96 and 98 switch demodulated reproduced audio signals so that, compared to switching FM audio signals inherently high in frequency, switching noise can be reduced if jitter occurs in the drum pulses.

As will be understood from the above description, the reproduced audio signal is delayed by one field period relative to the reproduced standard color video signal. However, one field period is about 1/60 or 1/50 second and such is negligible in practice.

Referring to Figure 9, a second embodiment of the playback system in accordance with the present invention is shown. In Figure 9, the structural elements commontothose shown in Figure 8are designated by the same reference numerals and description thereof will be omitted for simplicity. A video signal playback system in Figure 9 is identical with that of Figure 8 and, therefore, omitted. The second reproduced FM audio signal from the band pass filter 82 is applied to a delay and frequency converter 124.

The fourth reproduced FM audio signal output from the band pass filter 86 is fed to a delay and frequency converter circuit 126. The delay and frequency converters 124 and 126 are respectively adapted to produce one-field delayed FM audio signals having car rier frequencies fi and f2 by effecting one field of delay and frequency conversion. The relay and frequency converters 124 and 126, therefore, function in the same manner as the delay and frequency converters 52 and 56 in the record system and may be constituted by the latter.

The switch 96 receives the reproduced first FM audio signal having the carrier frequency fi output from the band pass filter 80 and the reproduced sec ond FM audio signal delayed by one field and having the carrier frequency f. output from the delay and frequency converter 124. The switch 96 switches the two inputs at every interval of one field period to combine them time-serially, applying an output thereof to the FM demodulator 128. The switch 98, on the other hand, receives the reproduced third FM audio signal having the carrier frequency f2 output from the band pass filter 84 and the reproduced fourth FM audio signal having the ca rrier frequency f.

Switching them at every interval of one field period, the switch 98 time-serially combines them to supply its output to the FM demodulator 130. The FM demodulators 128 and 130 respectively deliver left channel and right channel reproduced audio signals without interruption in the correct sequence.

The embodiment shown in Figure 9 is advantageous in that a single FM demodulation system suffices, and that the use of a memory for providing one field of delay renders the circuit construction simpler than one which relies on an analog delay element.

The first and second embodiments shown and described are only illustrative. Concerning the first and second FM audio signals, four different audio signals in total are written and read in the embodi ments since the audio signals in the right and left channels are individually modulated. Alternatively, summation and subtraction signals of the two chan nel audio signals may be modulated. While such modulated signals require a matrix circuit in the record and playback system, even a relatively inex pensive monophonic playback apparatus is capable of playing back a medium recorded with information by the system of the present invention. Also, the audio signals are not limited to two channel stereophonic audio signals and may be monophonic audio signals.

The audio signals may be written into or read out of a magnetic tape in a digital mode. The field delay circuits 24,30, 100 and 102 may comprise memories.

Further, the track width designed for the head HA may be wider than those of the heads H. and H2 since in this case, too, a guard band is defined between adja cent audio tracks although narrowerthan the width of video tracks.

Suppose that the left channel audio signal is L, the right channel audio signal is R, and signals prepared by delaying the signals L and R each by one track scanning period (one field period) where one field of data is to be written into one track) are DL and DR respectively. While in the embodiments the mod ulated signals of the FM audio signals having carrier frequencies f., ~2, B and f4 were DL, DR, R and L respectively, such is illustrative and may be replaced by the combination of L, R, DR and DL, that of R, L, DL and DR, or that of DR, DL, L and R. Moreover, none of the relations described between the modulated signals and carrier frequencies is restrictive ifthere is no need to satisfy the condition f. + f4 = f2 + f3.

In accordance with the present invention, even audio signals may be recorded overlapping each other(morethanonefield) byrecordingthembytime compression over a short period of time (about 90%) using BBD or the like, and expanding the playback time. This would enhance the accuracy in reducing switching noise.

Additionally,the buildup andfall of an audio signal which occur in the event of switching in the overlapping period may be provided with relatively slow inclinations to offer the fade-in and fade-out feature, thereby cutting down switching noise in a high frequency range.

In summary, it will be seen that the present invention provides a multiplex recording system and multiplex recording and playback system for VTR which features various advantages over prior art systems.

Because FM audio signals are written into a tape by a rotary head allocated exclusively thereto, mutural interference between FM audio signals and video signals due to beat between carrier frequencies is considerably reduced, compared to the prior art system which uses a single head for writing and reading multiplex FM audio and video signals. Audio tracks formed by the exclusive rotary head are located each in a same position as every second video track. This, compared to recording video and audio traks without superposition, does not shorten the record and playback time and, because a guard band is essentially defined by a video track between adjacent audio tracks, hardly entails cross-talk. The use of a single rotary head for writing audio signals cuts down the required numbers of heads and rotary transformers each by one than the case in which two exclusive rotary heads are employed, thereby simplifying the construction. The audio tracks may be provided with a larger width than video tracks and this offers a higher S/N ratio in reproduced audio signals than the case with commonly dimensioned audio and video tracks. Furthermore, switching noise is lowered since reproduced FM audio signals are FM demodulated and then time-serially combined through switches which are individually actuated at every interval of one track scan.

Various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.

Claims (18)

1. A multiplex recording system for a video tape recorder comprising: a rotary member around which a magnetic recording medium is wound over a predetermined angular range; at least two video signal recording rotary heads mounted on said rotary member at a predetermined spacing from each other, said rotary heads having azimuth angles which are different from each other and recording a video signal on the magnetic recording medium; a single audio signal recording rotatable head mounted on the rotary member in a position ahead of oneofthetwovideo signal recording rotary heads by a predetermined angle with respect to an intended direction of rotation of the rotary member, said audio signal recording rotary head having an azimuth angle which differs from the azimuth angles of the video signal recording rotary heads; and record processing means for producing from an audio signal fed thereto, a first frequency modulated audio signal, and a second frequency modulated audio signal which is delayed by one track scan period with respect to said first frequency modulated audio signal and for frequency division multiplexing said first and second frequency-modulated audio signals, supplying the multiplexed signal to the audio signal recording rotary head thereby said first and second frequency modulated audio signals are segmented to a time length of one track scan period and are recorded on the magnetic recording medium at every other track scan period forming tracks with one track space between adjacent tracks of the formed tracks, while the video signal recording rotary heads form video tracks of the video signal over the formed audio tracks.

2. A mutliplex recording system as claimed in claim 1, in which the azimuth angle ofthe audio signal recording rotatable head is substantially larger than the azimuth angles of the video signal recording rotary heads.

3. A multiplex recording system as claimed in claim 1, in which the video signal recorded by the video signal recording rotary heads is a frequency division multiplex signal made up of a frequencymodulated luminance signal and a low frequency range carrier color signal which occupies an empty band lower than a band of the frequency-modulated luminance signal, the first and second frequencymodulated audio signals being recorded in a band which neighbors a lower frequency limit of the frequency-modulated luminance signal.

4. A multiplex recording system as claimed in claim 1, in which the first frequency-modulated audio signal comprises two frequency-modulated audio signals which are different in band and produced by modulation signals which are audio signals in two channels of a two-channel stereophonic audio signal, the second frequency-modulated audio signal com prising two frequency-modulated audio signals which are different in band and produced by modulation of signals which are audio signals in two chan nels of a two-channel stereophonic audio signal.

5. A multiplex recording and playback system for a video tape recorder comprising: a rotary member around which a magnetic record ing medium is wound over a predetermined angular range; at least two video signal recording and playback rotary heads mounted on said rotary member at a predetermined spacing from each other, said rotary heads having azimuth angles which are different from each other; a single audio signal recording and playback rotat able head mounted on the rotary member in a position ahead of one of the two video signal recording rotary heads by a predetermined angle with respect to an intended direction of rotation of the rotary member, said audio signal recording and playback rotary head having an azimuth angle which differs from the azimuth angles ofthe video signal recording and playback rotary heads; and record processing means for picking up a first frequency-modulated audio signal from an audio signal which occurs at every interval of one track scan period and a second frequency-modulated audio signal delayed by one track scan period from an audio signal which occurs in at every another interval of one track scan, frequency division multiplexing said first and second frequency-modulated audio signals in a same one track scan period, supplying the multiplex signal to the audio signal recording and playback rotary head at an interval of every track scan period, controlling the audio signal recording and playback rotary head and the video signal recording and playback rotary heads such that the audio signal recording and playback rotary head forms on the magnetic recording medium an audio track which stores the first and second frequency modulated audio signals at a two-track pitch, while the video signal recording and playback rotary heads form video tracks which store video signals at onetrack pitch, the video track formed by the other video signal recording and playback rotary head being superposed on the previously recorded audio track; and playback processing means for discriminating and reproducing the first and second frequency-modulated audio signals from the reproduced signal picked up by the audio signal recording and playback rotary head which scans the track having the audio track and the video tracks superposed one upon the other, thereby time-serially synthesizing two demodulated audio signals from the first and second frequency demodulated audio signals.

6. A multiplex recording and playback system as claim claimed in claim 5, in which the azimuth angle of the audio signal recording and playback rotary head is sufficiently larger than the azimuth angles of the video signal recording and playback rotary heads.

7. A multiplex recording and playback system as claimed in claim 5, in which the video signal recorded by the video signal recording and playback rotary heads is a frequency division multiplex signal made up of a frequency-modulated brightness signal and a low range carrier color signal which occupies an empty band lowerthan a band ofthefrequency modulated brightness signal, the first and second frequency modulated audio signal being recorded in a band which neighbors a lower frequency limit of the frequency modulated brightness signal.

8. A multiplex recording and playback system as claimed in claim 5, in which the first frequency modulated audio signal comprises two frequencymodulated audio signals which are different in band and produced by modulation signals which are audio signals in two channels of a two-channel stereophonic audio signal, the second frequencymodulated audio signal comprising two frequencymodulated audio signals which are different in band and produced by modulation signals which are audio signals in two channels of a two-channel stereophonic audio signal.

9. Recording apparatus for a VTR, including first and second movable recording heads, for recording video information upon a magnetic medium, the first head being arranged to record video picture information and the second head being arranged to record video sound information.

10. A recording system as claimed in claim 9 wherein the azimuth angles of the first and second heads are different.

11. Playback apparatus, for a VTR, including first and second movable reproduction heads, for reproducing video information from a magnetic medium the first head being connected to picture processing means arranged to reproduce video picture information and the second head being connected to sound processing means arranged to reproduce video sound information.

12. Playback apparatus as claimed in claim 11 wherein the azimuth angles of the first and second heads are different.

13. A magnetic tape upon which video information has been recorded by the apparatus of claim 9.

14. A method of recording video information, which includes sound and picture components, upon a magnetic medium comprising the steps of separately processing the sound and picture components so that their respective major frequency components after processing do not substantially coincide and recording the sound information and at least some of the picture information in the same recording track.

15. A magnetic tape on which video information has been recorded by the method of claim 14.

16. Signal processing apparatus for processing an input signal including: delay means for generating a first signal, which is delayed by a predetermined amount; by-pass means for generating a second undelayed signal; modulating means so arranged to provide first and second modulated signals comprising carriers of different frequencies modulated in accordance with the delayed and undelayed signals respectively; and means for combining said modulated signals.

17. Video recording apparatus comprising: means for providing a sequence of first and second video signals, means for providing a sequence of first and second audio signals corresponding in time to said first and second video signals respectively, means for altering the relative timing of said audio signals to be coincident with one another, and means for recording the audio signals of altered timing together with one of said first and second video signals.

18. Multiplex apparatus as hereinbefore described with reference to the accompanying drawings.