[0001] This invention relates to a system for collecting statistics for audience research
into television use. In particular the invention relates to such systems to provide
information in respect of programmes being currently transmitted as well as pre-recorded
programmes being replayed in the home.
[0002] In collecting statistics for audience research into television use, it has been common
practice to use a so called TV meter to determine and record which channel is being
currently viewed so long as the programme being watched is an ON-AIR or live transmission
at the time that it is actually being broadcast or is being transmitted currently
via cable networks in real time.
[0003] The conventional TV meter has a severe limitation in respect of programmes which
were pre-recorded some hours, days or weeks earlier than the time at which the viewer
is playing back such a programme from a tape or other recording medium as would be
the case when a video cassette recorder (V.C.R.) is in use. In such circumstances
the conventional TV meter may be able to record that a V.C.R. was being used but it
would be incapable of identifying the nature of the programme being played back even
if the recording happened to be only a few minutes old. Neither could it identify
the TV channel which had originally broadcast it or the cable channel in the case
of cable TV.
[0004] Furthermore the conventional TV meter has another serious limitation namely that
although it is able to record details of live ON-AIR transmissions currently being
broadcast it is not able to identify individual advertisement as they are being seen
ON-AIR. It is also unable to identify a V.C.R. playback of a particular advertisement
being paid for by an advertiser for whom data is being collected by the audience researcher.
[0005] The invention has a prime objective, the provision of so-called V.C.R. TV meters
for collecting statistics for use in audience research capable of recording exactly
what programme is being watched live at the time the programme is being received in
a viewers home or what programme is being played back.
[0006] Further objectives of the invention include means of establishing:
(i) The time a V.C.R. recording was made in the home.
(ii) The channel from which the recording was reproduced.
(iii) The identity of an advertisement being viewed live or during V.C.R. playback,
or at the time the advertisement is being created.
(iv) With a single meter, a multiplicity of different channel identities all being
viewed or recorded at a given moment by a multiplicity of TV receivers or V.C.R's
sharing a common signal distribution network from antenna or cable.
Example 1. A V.C.R. television combination may be using two different channels at
the same time, one to be recorded whilst the other channel is being watched.
Example 2. In a multi-set home several TV's may be in use at any given moment all
watching different programmes.
[0007] In the ambit of this invention all of these objectives are attained using the one
technique of injecting known codes (signatures) into the intelligence being received
recorded or created; such codes to be recovered either instantaneously or at a later
time as evidence of the events that the codes depict. By "signature" is meant a descriptive
code or marker indicating a range of data or information.
[0008] There is provided according to the present invention a system of television audience
research comprising the steps of applying subliminal marker codes into a television/V.C.R.
installation encoding said marker codes detecting and decoding said codes in the television/V.C.R.
installation in real or subsequent time to obtain information as to programmes or
channels being watched recorded or played back, said codes permitting collection of
a range of data for the purpose of audience research.
[0009] When the advertiser produces his advertisement in the laboratory or studio, subliminal
codes may be added to the sound track. These codes may comprise an indentifier for
the advertising company eg. a serial number to identify a particular advertisement
in a series of many by the same advertiser. The coding is repeated frequently throughout
the tape recording of the advertisement, say between 10 and 30 times, according to
the duration of the advertisement, but more or less as may be deemed necessary.
[0010] The recording tape or film is then provided by the advertiser to the various television
channels and cable networks which the advertiser has chosen to transmit his advertisement.
[0011] The codes could alternatively be coded subliminally using single frames of just one
colour inserted into the picture information. By way of example only and not as the
only method possible, a single red frame (say) followed by 50 advertisement frames
followed by (say) a green frame and another 50 advert frames then (say) a blue frame
and 50 more advert frames and so on ad infinitum could provide several hundred identifiers.
[0012] Yet again it would be practical to represent the codes as digital information between
frames in the flyback period of the video information but this may not always be expedient.
[0013] Whatever the chosen method, it is only necessary to detect the codes superimposed
upon the received signal at the television receiver and to reconstruct the information
in a form suitable for recording in the meter memory for subsequent onward transmission
or reporting to a central computer which can then look up the codes and determine
the origin of the advertisement either being broadcast in real time or subsequently
played back at some later time.
[0014] To this information, the V.C.R./TV meter may append additional encoded details of
the date and time that the advertisement has been recorded, and from which channel,
or from which cable service, the broadcast or transmission originated.
[0015] The same method is used in the invention to add subliminal codes to the recording
medium of the V.C.R. or other recorder when in the process of taping an ON-AIR or
ON-WIRE programme magnetically. Upon playback the detector, which is of the type or
which could even be the same apparatus, used for recognising advertiser and advert
codes will also recognise the codes appended by the V.C.R./TV meter. These codes though
similar represent different data. This data could be a channel number code followed
by a record serial number which also includes date or such other information of use
to the audience researcher.
[0016] The need to provide such additional codes highlights a limitation of conventional
TV meters which are capable of only a single channel determination at a time.
[0017] In a typical V.C.R. installation the television receiver may be tuned to one channel
whilst the V.
C.
R. tuner is receiving programmes from a different channel for the purpose of recording.
[0018] Consequently two of the conventional type meters would be necessary. On the other
hand this invention allows multiple channel identification at the one time using a
single V.C.R./TV meter so that in fact any number of Television receivers or V.C.R's
sharing a common antenna system or cable system may be monitored by a single V.C.R/TV
meter even if all receivers and tuners are tuned to different programmes at any one
time.
[0019] At the time that the received broadcast is being recorded, the detector is on the
alert for subliminal advertiser codes present on the received signal from the originating
station or cable. These are allowed to pass directly to the recording head of V.C.R.
unchanged and during these moments, the subliminal channel number code and record
serial numbers generated repeatedly within the V.C.R./TV meter are inhibited so as
to avoid confusion, or contamination of the coded information. The meter generated
subliminal codes on the tapes, are constantly repeated whilst the playback is continuing
so that at all times the V.C.R./TV meter is aware of the identity of the material
(including advertisement) being played back and equally is aware of the source of
the play-back, unless that source be a film or similar pre-recorded video cassette
not received by direct electromagnetic radiation or by cable. In such event the V.C.R./TV
meter identifies "VIDEO" being played back knowing it to be either a FILM or VIDEO
by inference because these recordings will not contain any recognisable (to the V.C.R./TV
meter) subliminal codes.
[0020] The invention will be described in greater detail having reference to the attached
diagrams in which Figure 1 is a block diagram of a V.C.R./TV meter depicting those
parts relating to the invention concept as will become clear later. Other more conventional
aspects of TV meters are not shown.
Figures l(a) and l(b) show overall schematic arrangements of a V.C.R./TV meter.
Figure 2 shows a graphic representation of video signals played back from a V.C.R.
on a frame by frame basis.
Figure 2a shows video signals to the TV receiver, the missing pulse 20 and grey blanking
frame 21.
Figure 2b shows the FSK signals 22 to the modem from detector "e".
Figure 4 is a block diagram depicting apparatus for determining to what channel a
TV receiver is tuned at a given moment.
Figure 5 is a detailed block diagram of the encoder of Figure 4.
Figure 6 shows a block diagram of a further preferred embodiment for use with a marker
pulse.
Figure 7 is a block diagram of a multiple channel determination.
[0021] Figure l(a) shows one possible arrangement for a V.C.R./TV meter embodying this invention.
Figure l(a) is an outline schematic only and its individual component parts are described
in detail elsewhere in this specification in so far as they may relate to the novel
features of the invention. The microprocessor or computer M controls the entire apparatus
and processes the data gathered.
[0022] Under control of microprocessor or computer M, encoder A produces channel signatures
at all the possible frequencies available to the television receiver TV and V.C.R.
tuner VT and the broken line from encoder EA may carry confirmatory information back
to microprocessor or computer M.
[0023] Each channel signature is a unique code representative of one of the channels herein
called an A type code. This code is injected at IA into the radio frequency intelligence
arriving from the antenna and for the purpose of this description it will be in the
form of a sound modulated carrier but equally could be video modulated. When finally
demodulated, either at points p or q the codes may then be decoded by the A-Type Decoder
DA thus releasing back to computer or microprocessor M the identity of the channels
to which V.C.R. tuner VT or television receiver TV are tuned even should they be different
channels. Channel signatures for those channels not being used are suppressed by the
tuned circuits in the two receivers which are high frequency selective.
[0024] The channel code (A type) produced by the decoder DA is used, whenever the recorder
is operating, to activate encoder EB and inject it at IB as a video modulated carrier.
It could equally be a sound modulated carrier and constitutes a type -B code. This
code is then impressed on the magnetic recording which is being made. Later when play-
back is operative the code becomes once again available and is recognised by decoder
DB and hence passed to micro- processor M as an indication of the source (by channel
identity) of the original recorded programme.
[0025] The microprocessor M also uses encoder EB to append date and time codes in addition
to the channel code and when played back, all of this information describes the origins
of the recorded programmes. These are all called B-Type codes.
[0026] Decoder DB has one other function and that is to decode additional information as
to the programme being played back where such extra information has been encoded into
the original transmission from a broadcast TV transmitter (or cable network source)
as for example when an advertiser produces his video advertisement and encodes information
to identify himself and his advertisement. In such a case the codes appended to the
advertisement would need to be subliminal as are also the A and B type codes locally
generated within the V.C.R./TV meter.
[0027] Typically the advertisers code would also be produced using the format of the locally
generated B Type code if it were desired to use the same decoder DB although a different
format and an extra decoder to match may be added to the meter. The advertiser may
use an identical apparatus to that of the meter to produce his codes.
[0028] Figure l(b) shows the respositioning of IA of figure l(a) to suite injection into
a cable system. All other circuits and operations for cable TV are the same as described
for figure l(a).
EXAMPLES
[0029] 1. In figure l(a), should the television receiver TV be tuned to the frequency of
modulator MD and the programme being watched is tuned by the V.C.R. Tuner VT being
a different channel the two sets of information are delivered to the microprocessor
M.
(i) That receiver TV is on the V.C.R. fixed channel; and
(ii) That the programme being watched is from channel 'n' as tuned in by the controls
of the V.C.R.
[0030] 2. In figure l(b), the television receiver TV is always tuned to the frequency of
the cable irrespective of the programme being watched. This not withstanding, two
sets of information are again delivered to the micro- processor MPL
(i) That the receiver TV is set for cable viewing
(ii) That the programme being watched is from cable channel 'n'.
[0031] The A-Type codes are the mechanism used in both of the above examples to provide
this information.
[0032] One portion of the preferred embodiment of the invention is the arrangement depicted
in Figure 1.
[0033] This is a simplified block diagram of those parts of the V.C.R./TV meter which relate
to the novelty aspects of the invention.
[0034] Other parts of the V.C.R./TV meter not included in the drawing are details of the
control system for Tuning, the clock timer circuits, the controls for the tape deck,
and the method of recording which members of the household are viewing. These are
current state of the art and as such need no discussion here.
[0035] The arrangement of Figure 1 is mainly intended for those panel households which have
their own V.C.R., though in another preferred version of the invention, the V.C.R.
portion would be an integral part of the V.C.R./T
V meter to be installed by the researcher in a household elected for monitoring (panel
member).
[0036] In the circumstances depicted by Figure 1, the household's own V.C.R. is partially
demobilised as it will not have an antenna connected to its internal TUNER. The V.C.R.
internal TUNER is replaced by TUNER G in the
V.C.R./
TV meter Figure 1. All recordings made OFF-AIR by the V.C.R. are made via TUNER G and
its eventual outputs at V and W.
[0037] Yet another preferred arrangement includes interposing on RF Modulator between V
and W and sending the output of the RF Modulator into the antenna socket of the V.C.R.
which is then permanently tuned on its internal VCR TUNER to the frequency of the
RF MODULATOR. Once again, all OFF-AIR recordings come via TUNER G in the V.C.R./TV
meter Figure 1.
[0038] The household Antenna X in Figure 1 is connected to the two tuners B and G via a
conventional booster splitter A, which will compensate for any cable losses within
the wiring of the V.C.R./TV meter and to provide impedance matching.
[0039] FC in Figure 1 refers to an apparatus for injecting a marker pulse or a code (signature)
for each channel in turn whilst at the same time tuning an oscillator to the frequency
of that channel and injecting a subliminal marker or code into the stream of intelligence
coming from source X (In this case the antenna or as an alternative a cable terminal
device). The nature of FC is described later in this specification. Up to several
hundred channels may be catered for by FC.
[0040] Tuner B, provides OFF-AIR programmes to the domestic TV receiver. Audio at D and
Video at C are sent to RF Modulator F via switch E which is under the control of micro
processor M.
[0041] Switch E is a double pole changeover switch, which may be either a relay or electronic.
When viewing an OFF-AIR programme, this switch is thrown to the 'R' connection and
the output of TUNER B, via processing circuits in C and D modulate the RF Modulator
F to provide a signal in the VHF or UHF TV BANDS which enters the domestic TV receiver
antenna terminal at some suitable channel, say.3 or 36, depending on local conditions
in the area.
[0042] When switch E is thrown to the Pb connection, the play-back programme from the domestic
V.C.R. Cd is made available to the domestic TV receiver for viewing by the household
members. As the changeover of E is carried out by the microprocessor M, the latter
always knows whether the "system" as a whole is in play-back or record mode as set
by the viewer, or by the clock timer memory. "System" is defined as the composite
of Domestic TV, Domestic V.C.R., V.C.R./TV meter and various local or remote controls.
[0043] The description of switch E contacts as Pb and R meaning play-back-mode and record-mode,
does have some ambiguity of meaning.
[0044] In the so called RECORD mode the system may not actually be recording, but is available
to do so if called upon.
[0045] . In the RECORD mode, the TV viewer is actually watching the received signals from
TUNER B whilst the programme to be recorded via TUNER G may be the same as for TUNER
B, or some other channel selected by the viewer in both instances.
[0046] The RECORD procedure, when active, provides an Audio-out signal at W from where it
is sent to the V.C.R. Audio-in terminal.
[0047] The Video-out signal at V, serves the V.C.R. in like manner to the Audio-out signal
mentioned above, save that suitable data has been added by the V.C.R./TV meter.
[0048] In the version depicted by Figure 1, information to be encoded on the
V.C.
R. tape is transmitted to the V.C.R. in a time sharing mode with the OFF-AIR programme
to be recorded being received via TUNER G.
[0049] The means described here is not the only possible mechanism for coding the tape.
In Figure 1 the coding is done at CHROMANANCE frequency within the Video information
for the channel selected. It could equally be carried within the LUMINANCE FREQUENCY
BAND or even the Audio Band via suitable filters on a separate track if the V.C.R.
happens to be integral with the V.C.R./TV meter.
[0050] Video OFF-AIR signals from IF amplifier and detector, H are distributed to VERTICAL
SYNC. SEPARATOR J and then the vertical pulses 23 (Fig. 2(b) depicting picture frame
intervals are counted at K.
[0051] Counter K is preset to give an output impulse of one picture frame duration at predetermined
intervals, say once every 30 seconds, but not necessarily so.
[0052] Video OFF-AIR signals also go to a fast diode switch T via a DELAY S. This delay
may be as much as 64 u.s. or greater, or as little as 250 n.s. Anything in excess
of 64 u.s may be undesirable, as the delay plays a limiting role, even though a non-critical
one. In the process described, the purpose of the delay is to allow the diode switch
T sufficient time to transit to its other input coming from OSCILLATOR R. The approximate
frequency of R is 4 MHZ but not necessarily so.
[0053] In the quiescent state (as shown) switch T conveys the OFF-AIR video to the V.C.R.
via buffer U and terminal V.
[0054] As determined by the counter K, at regular intervals 6 goes low for one frame period
and the switch T cuts off the OFF-AIR Video to the V.C.R. and instead switches it
to oscillator R whilst preventing the vertical sync. pulse which initiated the transfer
from reaching the V.C.R. In the period of the switch-over the microprocessor M receives
an interrupt INT from the counter K via inverter L.
[0055] This causes the microprocessor to transfer data from its memory N to the Universal
asynchronous transmitter (portion of UART) O via the DATA BUS Y.
[0056] In turn this data is serialised within O and passed to TX Modem P.
[0057] Figure 1 shows a Modem P which may be 1200 BAUD, but this modem can operate at any
rate desired.
[0058] Modem P turns digital data streams from the UART O into frequency shift keying tones
(FSK) which are passed to Modulator Q which in turn frequency modulates OSCILLATOR
R.
[0059] Other preferred arrangements would permit alternative methods of modulation such
as amplitude, phase shift, amplitude controlled phase shift keying to mention a few,
and for different parts of the frequency spectrum to be used.
[0060] The data as selected by the microprocessor M is thus mixed into the OFF-AIR Video
stream for the duration of one picture frame, but not necessarily for such a precisely
defined period, e.g. ONE LINE of picture frame could be opted for. At the termination
of the period whatever its duration, switch T reverts to the quiescent state when
OFF-AIR Video is once again channeled out to the V.C.R.
[0061] The result is that hidden within the picture signals being recorded, a data stream
is also recorded and the data repeats or changes each time it is written on tape,
say once every 30 seconds by way of example.
[0062] At a subsequent play-back of this recording, the V.C.R. produces Audio which is fed
to switch E and then to the domestic TV receiver via RF Modulator F.
[0063] The Video signal from the V.C.R. enters the V.C.R./
TV meter via Buffer 'a' and is distributed three ways.
[0064] Its normal path is via delay 'b', say of 64 u.s. The purpose of the delay is to allow
time for the missing pulse detector 'i' to detect the start of the frame containing
coded information and to change-over the fast diode switch 'C' in time to prevent
coded information going to the TV receiver via the RF modulator F.
[0065] During the frame time when coded information arrives from the V.C.R., a blanking
frame 21 at grey signal (see Figure 2(a)) level and frequency is inserted into the
video stream which goes to the domestic TV. This grey signal is provided by OSCILLATOR
'd' under control of the missing pulse detector, 'i' (Q output). Another version of
the invention dispenses with this feature altogether. As soon as pulses 23 from the
VSYNC extractor 'h' resume, then the switch 'c' reverts to its normal quiescent state
supplying Video from the V.C.R. to the RF Modulator F and hence to the domestic TV
receiver.
[0066] Detector 'e' monitors the Video content arriving from the V.C.R., whenever it is
enabled by a signal from the Q output of the missing pulse detector 'i' which also
enables gate 'g'.
[0067] The output of detector 'e' reproduces the frequency shift keying tones originally
put on tape from TX Modem P, whenever they may be played back through the system.
[0068] These are translated to data bit streams by the RX Modem 'f', and passed to the universal
asynchronous receiver O (the other part of UART) via gate 'g'.
[0069] UART 0 conveys the data to memory N via the micro-processor M.
[0070] Suitable codes are generated by the microprocessor M when recording is taking place.
[0071] Typical examples of the codes used in a V.C.R./TV meter would be for
(a) Date and time of recording
(b) Channel being recorded
(c) Number of recordings made that day
(d) Recordings initiated by Timer Memory. although these are not the only codes or
information which the invention intends.
[0072] With reference to Figures 2, 2a and 2b, the description for Figure 1 would result
in only 2 characters of 8 bits each (TWO BYTES) or 4 Binary coded decimal characters
in one frame.
[0073] More characters would require higher Baud Rates or with the Baud Rate remaining at
1200, several frames at suitably designated intervals would be required.
[0074] Note: It is intended in the preferred system of Figure 1 that complete codes would
be repeated at regular intervals along the tape for the entire duration of the recording,
although not necessarily so.
[0075] It may happen that different codes are added to the video signals. One example of
such a code would be that of a particular Advertiser, when creating his advertisement
for distribution by commercial TV channels.
[0076] With reference to Figure 3, Advertiser Codes are received OFF-AIR and the Video Signals
containing them are fed to Detector 'e' Figure 1 and V Sync. extract 'h' Figure 1,
or when the system is in either play-back or record mode via 'ADD' 1 Figure 3.
[0077] For video from either source, the paths to the left of ADD 1 go to Missing Pulse
Detector 'i' Figure 1 and to Address Decoder 2. The appropriate one will detect data
present. For play-back video the description for Figure 1 applies.
[0078] For OFF-AIR-Video the grey frequency band is filtered out by narrow band NOTCH FILTER
3 and the resulting signals are applied to decoder 2.
[0079] When decoder 2 recognises an address it has been programmed to receive it enables
COUNTER 4.
[0080] This counts the number of FRAMES specified by the system designers as heralding the
arrival of an OFF-AIR DATA FRAME at some later point in time or it may actually be
that data and address are in the same frame.
[0081] The predetermined output of counter 4 enables Detector 'e' Figure 1 and gate 'g'
Figure 1 via OR (NOR) gate 5. The other input to gate 5 is the enable signal for play-back-video
via the MISSING PULSE DETECTOR 'i' Figure 1.
[0082] The counter 4 furnishes the enable signal to the data detector 'e' and gate 'g' Figure
1.
[0083] It may also be used to interrupt the microprocessor M Figure 1 to delay or inhibit
writing of locally generated codes to tape if TUNER G output is being recorded and
G TUNER is at the same Frequency as B TUNER. See Tl interrupt Figure 3.
[0084] To cover the situation where TUNER G is providing a different OFF-AIR programme to
that of TUNER B, it would be necessary to duplicate a portion of Figure 3 to detect
this OFF-AIR DATA and signal microprocessor M not to write locally generated codes
on top of OFF-AIR CODES.
[0085] Simply add a Notch Filter; Address Decoder; and another counter to Figure 1 on the
video distribution out of IF Amplifier 'H'.
[0086] The counter thus newly appended to Figure 1 can send a TO interrupt signal to microprocessor
M whenever a data frame is detected OFF-AIR via. TUNER G, Notch Filter and Address
Decoder, exactly as per the description of Figure 3 using identical components. It
is not required to decode the data arriving via TUNER G. It will be automatically
recorded on tape and can be decoded and stored in Memory N Figure 1 when it is played
back at some later time or date.
[0087] The concepts underlying the invention provide the means of determining to which channel
the TV receivers are tuned at any moment in time by injecting a coded message into
the antenna system such that a distinctive code by way of a signature is impressed
upon or intermingled with the signals being received by each TV receiver from time
to time.
[0088] In one preferred version of the invention; Figure 4 depicts the essential features.
[0089] PS represents the immediate source of the transmission being received by the TV receiver
be it from an antenna or a cable terminal.
[0090] FS is a fast electronic changeover switch controlled by the logic system of Figure
4 which may include a microprocessor but which can be caused to briefly interrupt
the received programme long enough to enable a coded message to be inserted in the
stream of signals coming from source PS said message coming from encoder E which is
shown in greater detail in Figure 5.
[0091] The coded message needs to be of such short duration that it becomes subliminal to
the viewer and this message which is actually a signature for the channel being watched
by the viewer may be either video or audio in character.
[0092] Figure 4 is representative of an audio signature system and for this case the Encoder
E also enables a second electronic switch SW at precisely the same instant that switch
FS is activated.
[0093] Switch SW cuts off the sound to the loudspeaker LS of TV receiver TV for a brief
period of time momentarily diverting it to decoder D.
[0094] Whenever decoder D recognises a valid signature or code the logic system is providing
the needed information regarding which channel is being watched at that point in time.
[0095] Switch SW is not always essential in that in another version of the invention decoder
D may be permanently connected to the sound output of the TV receiver TV or may even
be picking up the sound coming from loud speaker LS via a microphone. In this event
the decoder is programmed to look for an address code from the encoder E which precedes
the signature code. The decoder will thus ignore normal programme audio and only become
active when its address decode circuits signal that a channel signature is due to
arrive.
[0096] Figure 5 explains in greater detail one way in which the appropriate signature may
be generated by the encoder E so that whatever signature is recognised by decoder
D becomes significant.
[0097] Read only memory ROM may be programmed to hold signature codes for up to several
hundred channels. Such that for example address 1 of the ROM holds a signature for
channel 1 and address N of the ROM holds the signature for channel N. Of course this
form of address mapping is not mandatory.
[0098] Sequencer logic S is programmed to step the two oscillators 01 and 02 through all
the channels one by one or it may in fact skip channels not being used in a particular
locality and only those necessary may be programmed.
[0099] The appropriate oscillator 01 or 02 for a given channel is tuned by the tuning voltages
V
tv and V
tu as switched by the sequencer S such that the frequency of the oscillator selected
becomes identical to the frequency of the transmitter or cable system carrying the
programme for that channel.
[0100] Upon attaining the frequency of each channel in its turn then the enable and Read
outputs from the sequencer become active thereby operating switches FS and SW (fig
4) and the memory ROM.
[0101] As well as supplying the correct tuning voltage V
t to the appropriate oscillator 01 or 02 the sequencer addresses the read only memory
to select the signature code appropriate to that channel and the Read signal causes
that signature to be fed into the USART U which converts the signature into a bit-serial
signature is converted by modem Mm into audio tones which are then imposed upon the
oscillator selected via modulator Mr.
[0102] This results in the oscillator output being modulated with the audio content of the
channel signature as a digital data stream. The switch-enable control signals are
of sufficient duration such that switches FS and SW (fig 4) cause a momentary interruption
to the reception of the programme coming from source PS of figure 4 and inject the
signature into the TV receiver TV figure 4 antenna terminal at the same time diverting
the sound output of the TV receiver TV from loudspeaker LS to decoder D figure 4.
[0103] Only if the TV receiver is tuned to the channel currently selected by the sequencer
will there be an audio signature from the output of TV receiver. All other signatures
for channels not being watched will be inhibited from reaching the decoder D figure
4 by virtue of the selectivity of the RF circuits of the television receiver TV figure
4.
[0104] Figure 6 shows the outline of another preferred version of the invention which obviates
the need for an actual coded signature transfer. In this version only a marker pulse
is required so that an economy of injected information is achieved resulting in greater
numbers of channels available for identification within the available timescale.
[0105] The sequencer S acts exactly as in the previous example to inject a marker pulse
at each step as it passes through all channel frequencies in turn. This marker pulse
will only be detected when the frequency selected by the sequencer S matches the frequency
to which the viewer has tuned receiver TV.
[0106] The channel identity data is now available as a direct channel count in the form
of a digital code at the input to the random access memory RAM and when the Marker
Pulse Detector R recognises a valid marker it activates the WRITE signal which permits
the channel identity of the station currently being viewed to be recorded or otherwise
processed.
[0107] The fast switch FS figures 4 and 6 is not mandatory as alternative methods of impressing
the signature or marker pulse upon a continuous stream of itelligence coming from
source PS are readily available.
[0108] Figure 7 is included to illustrate the concept of more than one receiver being monitored
with different channels being watched.
[0109] In say a 200 channel cable environment the encoder E would step through or glide
through 200 frequencies effectively pausing at each sufficiently long to transmit
the code for that frequency or the marker. Typically the
200 markers could be served up in two milli-seconds or less which would be adequate
for a measuring system requiring readings once per minute. 200 coded signatures would
of course require a longer scan period.
[0110] In special cases readings for particular channels may from time to time be required
to be done at say 3 second intervals. In such cases the encoder could be programmed
to select those channels more frequently than the others at certain times of the day
or as commanded by a central computer using radio to remote control the V.C.R./TV
meter, or even using the cable system itself for such purpose.
[0111] In figure 7 PS, FS, and E have the same functions as they do in the earlier drawings.
[0112] The distribution amplilfier DA would be a normal part of the building TV system for
say flats or units or multi-set households.
[0113] Decoders 1 to 12 are fitted with short term memory to latch the codes as and when
received and to hold that code until a new one arrives.
[0114] Multiplexer MP is a convenient way of channeling the results to a common processor.
[0115] A complete scan of all available channels is only required occasionally.
[0116] Having determined that a given TV is tuned to channel 'n' then the injection oscillators
may be held at the channel 'n' frequency until such times as the marker or code is
no longer returned to the computer.
[0117] This signals a change of channel being viewed or an OFF condition and so a single
complete scan is again called for.