GB2223915A - Record/playback method and apparatus - Google Patents

Abstract

For the record/playback of two information signals, which may represent the respective components for stereo audio or other unrelated information, the two signals are applied via a matrix 10, or directly, to switches 11, 12 such that, in the case of stereo audio, the sum (L+R) and difference (L-R) are derived with the addition of a low frequency ident tone to the difference signal whilst, in the case that the signals are not stereo audio, the signals are derived unaltered. The derived signals are applied to the tape and, on playback, are applied to a further matrix 17, or directly, to further switches 22, 23. When the recorded signals represent stereo audio the ident tone is extracted by filter 19 and tone detector 20 to control further switches 22, 23 to produce the respective L and R signals. In the case that these signals are not stereo audio, a selected one of the information signals is derived from the further switches. <IMAGE>

Description

DESCRIPTION RECORD/PLAYBACK METHOD AND APPARATUS The present invention relates to a record/playback method for an information system which comprises first and second information signals which signals may represent respective first and second components for stereo audio or other information which is unrelated. The invention also relates to apparatus for use with such a method.

Such an information system may be used with a television signal to provide either stereo sound signals to accompany the vision information or alternatively two separate mono sound signals, which may be in different languages, for the vision information. A system of this type and known as the "Zweitontregerverfahren" has been adopted in the German Federal Republic and is disclosed in EP 0014348 B1. In this system, in the presence of a stereo sound signal, the normal 5.5MHz subcarrier is modulated by the sum of the left (L) and right (R) signals (L + R) whilst a second subcarrier at 5.742MHz is modulated by twice the right signal (2R). When two languages are to be transmitted the two subcarriers are each modulated by a respective language signal.A further system which has become known as "NICAM 728" has been adopted in the United Kingdom, details of which can be found in the publication "Specification of a Standard for UK Stereo-with-Television Transmissions" from the BBC Engineering division of the British Broadcasting Corporation dated September 1986 or the revision of this specification as contained in the later document "NICAM 728: Specification for two additional digital sound channels with System I television" published by the Independent Broadcasting Authority (IBA), the British Radio and Electronic Manufacturers Association (BREMA) and the British Broadcasting Corporation (BBC) dated August 1988. In this latter system an additional subcarrier is provided at 6.552 MHZ which is digitally modulated by the information signals, this being in addition to the usual sound modulated subcarrier at 6MHz.The NICAM 728 system alternately provides for the digital sound carrier to contain one mono sound signal and one 352 kbits/s transparent data channel or as a further alternative one 704 kbit/s transparent data channel.

Both of the above systems additionally contain control signals which indicate the nature of the signals being transmitted e.g. stereo sound, or dual mono sound, or single mono sound plus data, etc., and allow for mode switching at the receiver. However a problem exists when such stereo or mono sound signals are recorded as although the two audio signals or channels can be recorded the control information is not so recorded and on playback there is no information as to the nature of the two signals i.e. whether they are a stereo pair or dual mono. Such information can be particularly important in the case of broadcasts from commercial television stations where a programme accompanied by sound in two separate languages (dual mono) is periodically interrupted by advertisements accompanied by stereo sound.If one or other of the two languages is selected on replay then when stereo sound is present only one of the stereo components will be heard. This could be overcome by some form of manual switching, either at the recorder or at its remote control, but its continual use could become inconvenient.

The mono sound/data channel option would also provide such a problem.

It is an object of the invention to provide a method and apparatus which can be used to overcome the above problem.

The present invention provides a record/playback method for an information system which comprises first and second information signals which signaLs may represent first and second components for stereo audio or other information which is unrelated, said method in the record mode comprising the steps of:: i) deriving said first and second information signals, ii) applying said information signals, or signals derived therefrom, to a first pair of paths, iii) summing said signals in said first pair of paths to produce in the case of stereo audio, the sum (L + R) and the difference (L - R) from left (L) and right (R) signals, iv) applying said (L + R) signal to first switch means, v) combining said (L - R) signal with an ident tone to produce a modified (L - R) signal, vi) applying said modified (L - R) signal to second switch means, vii) applying said information signals, or signals derived therefrom, to said first and second switch means by way of a second pair of paths, viii) controlling said first and second switch means from a control signal or signals of said information system such that in the case of stereo audio said first switch means selects said (L + R) signal and said second switch means selects said modified (L - R) signal and in the absence of stereo audio said first and second switch means select the first and second other information signals.

xi) recording first and second signals so selected on a recording medium, said method in the playback mode comprising the steps of: x) reproducing said first and second selected signals from said recording medium, xi) applying said reproduced first and second signals to a third pair of paths, xii) separating said signals in said third pair of paths to produce, in the case of stereo audio, the respective L and R signals, xii;;) applying said L signal to third switch means and said R signal to fourth switch means, xiv) applying said reproduced first and second signals through a third pair of paths to a fifth switch means for selecting one of said reproduced first and second signals and applying that signal to said third and fourth switch means, xv) controlling said third and fourth switch means in response to said ident tone, when present, such that in the case of stereo audio said third switch means selects said L signal whilst said fourth switch means selects said R signal and in the absence of stereo audio said third and fourth switch means select that signal selected by said fifth switch means.

The invention also provides apparatus for use with the above method.

The accompanying drawing shows in block diagram form, and by way of example, part of a video tape cassette recorder (VCR) for use with the present invention. Those parts of the VCR which perform the various functions associated with the recording and playback of the video signal have been omitted as they are not important for an understanding of the invention and it is only necessary to state that the VCR may use the VHS or other suitable system.

It is assumed that the VCR is suitable for use with a television transmission system which can carry two audio signals such as what has become known as the NICAM 728 system as mentioned above, it being possible with this system to transmit in digital form on the digital sound carrier either the left (L) and right (R) audio signals of a stereo pair, or two independent mono sound signals, or one mono sound signal plus a 352 kbit/s data channel, or a 704 kbit/s data channel. For the present it is only necessary to consider the first two alternatives.

In the drawing an aerial 1 is shown connected to a tuner/demodulator 2 in the VCR to provide UHF television signals, some of which will include the additional NICAM 728 signal. The unit 2 produces at a first output 3 the demodulated video signals for further processing whilst a second output 4 produces the NICAM digital signals which are applied to a NICAM decoder 5.

The pre-selected decoded signals are applied over a connection 6 to a digital-to-analogue (D/A) converter 7 to produce two audio signals on connections 8 and 9. If a stereo signal is present then the connection 8 will carry the L signal whilst connection 9 will carry the R signal whilst if two mono sound signals M1 and M2 are present these will be respectively carried by connections 8 and 9.

The connections 8 and 9 are respectively connected to inputs L and R of a matrix 10 which in the case of a stereo signal produces from the L and R signals the sum and difference of these signals (L + R) and (L - R) at indicated outputs. The (L + R) output is connected to a terminal A of a first change-over switch 11 whilst the (L - R) output is connected to a terminal A of a second change-over switch 12 via an adder circuit 13 which switches are ganged and shown in their stereo position. The NICAM 728 signal also contains four bits of control information, three of which, namely C1, C2 and C3 indicate the nature of the information signals being carried. An output 15 of the NICAM decoder 5 carries a signal derived from this control information which indicates the presence or absence of a stereo sound signal (STEREO/DUAL MONO) to control switches 11 and 12.In order to indicate that a stereo sound signal is present a stereo ident tone is added in the adder circuit 13 to the (L - R) signal which tone is produced by a stereo ident tone oscillator 14. The difference signal (L - R) tends to be biased towards high frequencies as the L and R signals tend to be in phase and similar at low frequencies. Thus the ident tone can conveniently lie between 10Hz and 50Hz.

In the presence of a stereo signal the outputs of switches 11 and 12 are connected to their A terminals as a result of which the (L + R) signal is applied to a first track TRK 1 on a magnetic recording tape 16 or any other suitable recording medium whilst the modified (L - R) signal which includes the ident tone is applied to a second track TRK 2 on the tap 16.

In the presence of two mono signals M1, M2 on the connections 8 and 9 and which are respectively connected to the B terminals of switches 11 and 12, the output 15 from NICAM decoder 5 causes the outputs of switches 11 and 12 to be connected to their B terminals so that mono signal M1 is applied to TRK 1 on tape 16 whilst mono signal M2 is applied to TRK 2 on that tape.

When set to operate in the playback mode the signals recorded on the two tracks on the tape 16 are reproduced with that on TRK 1 being applied to an (L + R) input of a matrix circuit 17 whilst that- on TRK 2 is applied to an CL - R) input of matrix circuit 17 via a bandstop filter 18 which prevents the passage of frequencies around that of the ident tone. The signal on TRK 2 is also applied to a bandpass filter 19 which passes frequencies around that of the ident tone and applies the ident tone, when present, to a tone decoder 20 for the purpose as will hereinafter be described.When the tracks TRK 1 and TRK 2 respectively carry the (L + R) and modified (L - R) signals for the stereo pair these signals, with the ident tone removed, are applied to the associated inputs of the matrix circuit 17 where the L and R signals are separated and presented to respective L and R outputs.The ident tone present in the modified (L - R) signal from TRK 2 is extracted therefrom and its presence detected by tone decoder 20 to produce an output on a line 21 indicating the presence or absence of a stereo signal (STEREO/DUAL MONO). In the presence of a stereo signal the signal on line 21 causes a pair of ganged change-over switches 22 and 23 to have their outputs connected to their A inputs to which the L and R outputs from matrix circuit 17 are connected, the outputs of switches 22 and 23 being connected to respective first 24 and second 25 outputs of the playback arrangement which respectively receive the L and R signals. These outputs 24 and 25 can be connected to respective channels of an audio amplifier and loudspeakers (not shown).The signal on output 21 may additionally be connected to a stereo beacon 26 in the form of a LED which is illuminated when the ident tone is present in the modified (L - R) signal.

The signal from TRK 1 is additionally applied to the A terminals of a change-over switch 27 and a further change-over switch 28 whilst the signal from TRK 2, after passing through band-stop filter 18, is additionally applied to the B terminal of these two ganged switches 27 and 28. These switches are operated by the VCR user to select, in the absence of a stereo signal, which of the mono sound signals M1 or M2 is required. When a stereo signal is not present signal M1 will be reproduced from TRK 1 whilst signal M2 will be reproduced from TRK 2. With switches 27 and 28 in their positions as shown (B) their outputs will both carry the mono sound signal M2 whilst in their other position (A) both switch outputs will carry the mono sound signal M1.It is preferred that these switches 27, 28 would default to their A positions. In the absence of the tone ident the switches 22 and 23 will be in their positions other to that shown with their B terminals connected to the outputs of switches 27 and 28. In such a case the selected output from switches 27, 28 will appear at both the outputs 24, 25 of the playback arrangement.

With the above described method the VCR user, on playback, is able to select, in the case of two mono sound signals, which of these signals it is wished to be reproduced CMl or M2).

Should these signals be interrupted by items containing a stereo signal, such as advertisements on a commercial television channel, the switches 22 and 23 will move to their A positions in the presence of the ident tone to reproduce the stereo signal. Obviously in the record mode the switches 11 and 12 will change from their B to their A positions in the presence of the ident tone to reproduce the stereo signal. If on playback in the presence of a stereo signal the ident tone should not be detected or for some reason is absent, the switches 22 and 23 will default to their B positions to provide the L + R signal at both outputs 24, 25. After the stereo item, the system reverts to dual mono sound then the selected mono signal will continue to be reproduced.

The above description relates to stereo sound and dual mono. It will be appreciated that the operation will be similar when one of the mono sound signals is replaced by a data signal though this may not be suitably recorded and played back.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the design, manufacture and use of methods and apparatus and component parts thereof and which may be used instead of or in addition to features already described herein. Although claims have been formulated in this application to particular combinations of features, it should be understood that the scope of the disclosure of the present application also includes any novel feature or any novel combination of features disclosed herein either explicitly or implicitly or any generalisation thereof, whether or not it relates to the same invention as presently claimed in any claim and whether or not it mitigates any or all of the same technical problems as does the present invention. The applicants hereby give notice that new claims may be formulated to such features and/or combinations of such features during the prosecution of the present application or of any further application derived therefrom.

Claims (6)

CLAIM(S)

1. A record/playback method for an information system which comprises first and second information signals which signals may represent first and second components for stereo audio or other information which is unrelated, said method in the record mode comprising the steps of: i) deriving said first and second information signals, ii) applying said information signals, or signals derived therefrom, to a first pair of paths, iii) summing said signals in said first pair of paths to produce in the case of stereo audio, the sum (L + R) and the difference (L - R) from left (t) and right (R) signals, iv) applying said (L + R) signal to first switch means, v) combining said (L - R) signal with an ident tone to produce a modified (L - R) signal, vi) applying said modified (L - R) signal to second switch means, vii) applying said information signals, or signals derived therefrom, to said first and second switch means by way of a second pair of paths, viii) controlling said first and second switch means from a control signal or signals of said information system such that in the case of stereo audio said first switch means selects said (L + R) signal and said second switch means selects said modified (L - R) signal and in the absence of stereo audio said first and second switch means select the first and second other information signals.

xi) recording first and second signals so selected on a recording medium, said method in the playback mode comprising the steps of: x) reproducing said first and second selected signals from said recording medium, xi) applying said reproduced first and second signals to a third pair of paths, xii) separating said signals in said third pair of paths to produce, in the case of stereo audio, the respective L and R signals, xiii) applying said L signal to third switch means and said R signal to fourth switch means, xiv) applying said reproduced first and second signals through a third pair of paths to a fifth switch means for selecting one of said reproduced first and second signals and applying that signal to said third and fourth switch means, xv) controlling said third and fourth switch means in response to said ident tone, when present, such that in the case of stereo audio said third switch means selects said L signal whilst said fourth switch means selects said R signal and in the absence of stereo audio said third and fourth switch means select that signal selected by said fifth switch means.

2. A method as claimed in Claim 1, wherein said ident tone is located in the low frequency portion of said (L - R) signal.

3. A record method substantially as herein described with reference to the accompanying drawing.

4. A playback method substantially as herein described with reference to the accompanying drawing.

5. Apparatus for use with the method as claimed in any of the preceding claims.

6. Record/playback apparatus substantially as herein described with reference to the accompanying drawing.