Abstract: In a video tape recorder of the rotary two-head helically scanning type, a magnetic recording/reproducing system provided with a mode judging device in which a video signal is recorded onto a recording track in a multiplex manner together with a pilot signal for use in judgement of the recording time mode and when the record is reproduced the pilot signal is detected to thereby judge the recording time mode.

Abstract: A control signal recording and reproducing system for exactly tracking a record track in a helical scan type VTR or the like is disclosed.Intermittent pilot signals are recorded with the frequency spectra thereof being interleaved between adjacent tracks. In a reproducing operation, the main track pilot signals and the adjacent track pilot signals are separated by a comb type filter, and using a time position of the main pilot signals as a reference, the adjacent track pilot signals are separated in time to the front adjacent track pilot signal and the rear adjacent track pilot signal to detect the direction of a tracking error.

Abstract: A data recording/reproducing apparatus simultaneously records parallel data in recording tracks the number of which corresponds to the number of parallel data to be recorded, and sequentially reproduces the contents of the recording tracks to form serial data. A plurality of video signals for cooperatively forming a single picture are used for the parallel data. When one picture is quartered, four parallel video signals are simultaneously recorded in four recording tracks. By reproducing the contents of the recording tracks for each track in a sequential manner, one serial video signal corresponding to the picture is obtained. With this arrangement, high resolution picture data obtained from a solid-state image pickup device can be recorded and reproduced without the use of a specially designed parallel/serial converter.

Abstract: Apparatus for correcting the distortion in the output of a playback device introduced by wow and flutter by sampling a constant frequency as reproduced and comparing it with the signal as originally recorded to produce a correction signal for modulating a delay device coupled to the output of the playback device.

Abstract: In a subscription television system, only a video signal for a specific program is scrambled in a television signal in accordance with a predetermined scrambling mode. A key signal, used for unscrambling the scrambled video signal, is generated in response to the scrambling mode. The key signal is transmitted after the scrambled program.

Abstract: A video signal recording/reproducing apparatus includes a recording medium having a video track and an audio track separately formed, wherein a video signal is recorded in the video track and an audio signal to be multiplexed and a discrimination signal of a low frequency and a low level representing the kind of multiplexing thereof are recorded in the audio track. Decision is made of the kind of multiplexing of the audio signal, such as a bilingual mode, a stereo mode or a monaural mode, as recorded in the audio track, in response to the descrimination signal reproduced from the audio track and a multiplexed audio signal is produced in response to the decision signal representing the kind of the audio signal and the audio signal reproduced from the audio track.

Abstract: A method is disclosed for verifying the integrity of servo data stored as a series of parallel servo tracks on a disk. Each track includes automatic gain control data and servo positioning data. The peak amplitudes of the automatic gain control pulses on a first track determine a first effective threshold or AGC gain level. The first threshold level is then shifted to a higher, enhanced threshold level. Servo data pulses from a second track are then detected, based on the enhanced threshold level and the AGC gain level of the first track. Should these servo data pulses not be fully detected, an error is recorded for the second servo track.

Abstract: In accordance with a method of recording and/or reproducing stereophonic information in two adjacent tracks of a magnetic record carrier, an auxiliary signal whose frequency content is situated outside the frequency spectrum of the stereophonic information is recorded in the tracks and in the magnetic record-carrier area between the tracks during recording. During reproduction, the auxiliary signals read from the record carrier by the two transducers is used to control the gain of a pair of variable amplifiers so as to ensure that the amplitudes of the stereophonic information signals thus reproduced are independent of tracking errors.

Abstract: The invention provides for the recording of an audio message and subsequent playback thereof and includes a facility for establishing whether the playback message is an authentic reproduction of the original message. The facility is obtained by producing a first data signal indicative of the audio message and recording it together with the audio message and producing a second data signal indicative of the playback message, and comparing the first and the second data signals to establish that the playback is an authentic reproduction of the original message if parity exists between the data signals.

Abstract: A video disc recording and reproducing system in which a program is stored on a video disc to eliminate the need for the user to manually input a control program. A program and control signal is recorded in place of at least a portion of one of two audio tracks on a video disc along with video signals. The video disc player of the system includes modulator circuits which demodulate the video and audio signals from the disc, a central processing unit connected to the output of the demodulator circuit for demodulating the audio signal for detecting the control signal and program recorded on the video disc, and a memory for storing the control signal and program. The central processing unit controls the memory for storing the program and control signal at predetermined locations corresponding to the state of the control signal.

Abstract: The present disclosure describes an electronic system for use with low cost audio tape recorders whereby a substantially noise-free wide dynamic range is provided for the recording of analog signals in the DC to 30HZ frequency band. In achieving this result, the system utilizes two FM carrier oscillators having center frequencies displaced from each other and modulated respectively in opposite senses by the signal being recorded. The system also provides an additional utility channel of limited dynamic range for the concurrent recording of time markers, digital signals and the like.

Abstract: A method for automatic control of non-linear image processing of a television signal subjected to degradation upon passage through a quality degrading medium is disclosed. The processing is of the type including at least one of image enhancement, and noise, ringing and interference reduction within the television signal. The method includes the steps of:a. generating a pilot signal having an amplitude and frequency selected to be representative of video transitions most susceptible to degradation during passage through the medium;b. adding the pilot signal to the television signal prior to its passage through the degrading medium and before any prepassage signal processing takes place;c. passing the television signal through the degrading medium;d.

Abstract: A method of recording and reproducing audio signals and corresponding visual signals in parallel tracks extending in the longitudinal direction on a magnetic tape, includes the steps of recording the audio signals in first and second primary tracks on opposite sides of the tape in the widthwise direction thereof; and alternately recording a first visual information signal corresponding to the audio signal in the first primary tracks and a second visual information signal corresponding to the audio signal in the second primary tracks in a single secondary track positioned in the center of the tape in the widthwise direction thereof, the first visual information signal being recorded in first information blocks in the secondary track and the second visual information signal being recorded in second information blocks in the secondary track in an alternating relation with the first information blocks such that only the first visual information signal is reproduced when reproducing the audio signal from the first

Abstract: In an apparatus for recording and/or reproducing a television signal with multiplex audio signals, a pilot signal is recorded on one or both of the audio tracks of a video tape in a manner to identify the mode of the multiplex audio signals and each pilot signal is detected to establish such mode when reproducing. For example, the frequency of the pilot signal may be changed for identifying different modes of the multiplex audio signals, such as, the bilingual mode and the stereo-phonic mode, with the pilot signal of selected frequency being recorded on one of the audio tracks, or the pilot signal having a certain frequency is recorded on one of the audio tracks in the case of the bilingual mode, and on the other audio track of the tape in the case of the stereo-phonic mode. In still another embodiment, the pilot signal is recorded in both audio tracks of the tape and the phase relation of the recorded pilot signals is varied to identify the mode of the multiplex audio signals.

Abstract: A video recorder has a first transducer which moves with respect to a moving tape to selectively record and play back video information; the tape has a control region which is accessed for recording or playback by a second transducer. Storing means external of the tape store first coded indicia. Generating means responsive to the storing means is connected to the second transducer for generating second coded indicia to be recorded in the control region simultaneously with the recording of video information by the first transducer, provided the second coded indicia has a predetermined relationship with the stored first coded indicia. During playback signals recorded on the control region are utilized for synchronizing the relative movement between the first transducer and the second transducer and the tape.

Abstract: In one exemplary embodiment errors due to tape flutter are overcome by recording along with the analog signal clock pulses having a rate sufficient for sampling of the highest frequency component of the analog signal. Then on playback, the reproduced clock pulses control sampling and storage of samples of the reproduced analog signal. By reading out the samples from storage at a uniform clock rate, the effect of flutter on the reproduced signal is eliminated. In another example the recorded clock rate overcomes tape skew and other mechanical irregularities in recording and reproducing multiplexed analog or digital data.

Abstract: A signal indicative of tape tension or of recording of signal on tape is generated in a helical-scan recorder. A test signal having a particular frequency characteristic is recorded by rotating heads at a high head-to-tape speed. A fixed playback head downstream from the headwheel picks up the test signal converted in frequency by the ratio of the reading speed to the writing speed, and applies it to a detector. The detector is a synchronous detector which receives at a second input terminal a frequency-divided sample of the test signal which controls demodulation by the synchronous detector. The frequencies of the input signals to the phase detector differ by a small amount, so that an output signal can always be generated no matter what the phase of the input signal. The rate of pulsation of the output signal is indicative of tape tension.

Abstract: A magnetic recording and reproducing apparatus, for recording and reproducing the color television signal including VIR signal, of the type having a comb filter which is inserted in the chrominance signal system and includes a delay line for causing a delay equal to one horizontal line scanning period. In this apparatus the VIR signal has no line correlation so that the output of the comb filter becomes a VIR signal the amplitude of which is reduced by 6dB and that the amplitude and/or phase of the chrominance components of VIR signal are caused to vary over a wide range due to the effects of VIT signal.

Abstract: In a cue signal generating system applied to a tape recorder which detects a cue signal by a reel drive of the tape, there is produced at least two different cue signals having the following relationf1/f2>d1/d2where d1 is the maximum wound tape diameter of the drive reel for the tape used, d2 is the minimum wound tape diameter of the drive reel, f1 is first frequency information contained in a first cue signal of a plurality of different cue signals and f2 is second frequency information of a second cue signal which is lower in frequency than said first frequency information f1.

Abstract: At least one channel of digitized information is recorded in a selected number of data tracks by a record medium. The digitized information is encoded, modulated and then recorded in a predetermined number of tracks. For example, if n channels of digitized information are to be recorded in m data tracks, then each channel is recorded in m/n data tracks (m.gtoreq.n). A control signal is generated to include control data representing at least one of the following: (a) the number of data tracks in which each channel of digitized information is recorded, (b) the encoding scheme used to encode the information, (c) the type of modulation used to modulate the encoded information and (d) the relative speed of movement of the record medium. The control signal is recorded in a separate control track. Thus, the control signal represents the particular format in which the digitized information is recorded.

Abstract: A system for reproducing and/or transmitting analog audio information is disclosed which provides for the correction of time base errors. An inaudible pilot signal accompanies the audio information. Correction circuitry examines the frequency and phase characteristics of the pilot signal to develop signals for effecting correction of the errors.

Abstract: An apparatus for recording and detecting a cue signal which comprises:a recording section (100) for recording in a recording medium a composite cue signal formed of a component signal having a first frequency (f1) and denoting a tape speed pattern and another immediately following component signal having a second frequency (f2) and representing a cue signal pattern; anda detecting section (200), which, at the time of reproducing said composite cue signal, compensates a component signal which represents a cue signal pattern and is detected immediately after a tape speed pattern component signal drawn out of the recording medium in proportion to the period (T10) of said tape speed component signal, andwhen said composite cue signal is recorded in said recording medium, provides data on a cue signal pattern on the basis of the compensated component signal denoting a cue signal pattern.

Abstract: A magnetic recording and reproducing system is disclosed in which a frequency-modulated input signal is recorded on a magnetic medium together with a further signal which is discriminative from the frequency-modulated signal. The recorded frequency-modulated signal and further signal are frequency-demodulated so that the former reverts to the input signal and the latter represents an FM noise signal which is generated due to the wow and flutter during the recording and/or reproducing process. The extracted noise signal is mixed with the reproduced input signal thereby canceling an FM noise component in this reproduced signal. The mentioned further signal may be an amplitude-modulated signal of or a carrier wave signal for the frequency-modulated input signal.

Abstract: A magnetic recording and reproducing device including two video tape recording and reproducing portions each of which have tape systems including supply reels, rotatable head drum assemblies, a tape drive capstan, a take-up reel, and wherein said tapes can be driven in either the forward or reverse directions and normally are driven intermittently and alternately in the forward direction and subsequently alternately and intermittently in the reverse direction with means for providing a longitudinal control signal on said tapes in both the forward and reverse directions as well as means for recording slant video tracks alternately on the tapes during a time when a particular tape is stopped and with adjacent slant tracks on one tape being the odd fields, and the adjacent slant tracks on the other tape being even fields, and wherein between each recording in one direction is spaced a sufficient distance apart from the next recording so that intermittent recording can be placed therebetween when the direction of

Abstract: A method and apparatus for recovering analog signal information from a multiple-track information storage medium such as a magnetic tape is based upon time base error correction of a frequency modulated carrier signal. In one embodiment, the phase difference of a pair of pilot signals recorded on tracks adjacent a data track is compared by a sampling and pulse counting technique to eventually produce a trigger signal for a phase-locked oscillator. The output of the phase-locked oscillator is employed to sample and measure the period of the input data signal. The period values are written as digital values into a digital first-in first-out buffer memory. A stable clock is used to read out the contents of the buffer memory which are thereafter converted to a pulse rate modulated pulse train. The pulse train is converted to a useable analog signal by a pulse rate to frequency converter.

Abstract: The present invention relates to a method and device for associating auxiliary information with principal information, and to a device for monitoring the reproduction of principal information recorded on a track, whereby the auxiliary information is coded in an auxiliary signal of limited frequency and superposed on the principal signal, to be recorded in said track. The device comprises a detection circuit connected at the output of the reader head to detect an auxiliary signal associated with the principal information and occupying a limited range of frequencies and a recording device for recording the auxiliary information. The invention is more particularly applied to the monitoring of the public reproduction of recordings.

Abstract: A method and apparatus are provided for detecting a splicing point in a magnetic medium on which a sequence of normally periodic control signals have been recorded. The sequence of control signals is reproduced and a periodic anticipative signal is generated which has an anticipated phase relationship with expected control signals reproduced from the magnetic medium. The phase relationship between the actually reproduced control signals and the anticipative signals is detected and a splicing point is indicated when the detected phase relationship between these two signals deviates by more than a predetermined amount from the anticipated phase relationship.

Abstract: A method of locating a splice within an endless loop of magnetic tape by detecting the presence of a magnetic marker attached to the magnetic recording tape wherein the magnetic marker is comprised of a magnetic layer having a flux density of at least 0.05 line of flux per centimeter of width, a thickness of not greater than 60 microns, and a coercivity of at least 1,000 oersteds, and which has a detectable magnetic pattern recorded thereon.

Abstract: Apparatus for compensating for the absence of signals among a plurality of correlated signals, which occur simultaneously and which have carrier components, is disclosed herein. Such apparatus comprises detector means responsive to the absence of the carrier for longer than a predetermined time for selectively connecting output signals from channels where the carriers are present to the outputs of those channels where carriers are absent. The apparatus of the invention operates in real time without delay devices. Preferably, the invention is embodied in an apparatus for reproducing magnetically recorded, stereophonic signals, functioning to prevent dropouts from affecting the quality of the output signals and the sound corresponding thereto.

Abstract: A device for adjusting the frequency response characteristic of a magnetic sound recorder at relatively low and high frequencies, wherein the signal level of the recording signal to be supplied to the recording head of the recorder and the amount of compensation for the frequency response characteristic of the recording signal are adjusted by visual observation of a visible signal produced by one of electrically actuated light-emissive semiconductor elements which are to be selectively energized depending upon the relationship between the signal level of the playback signal and a reference signal which may be one of a plurality of predetermined reference signals or may be variable with the level of the recording signal.

Abstract: A video tape recording apparatus with the use of an Hadamard transformation system is disclosed. The apparatus comprises means for distributing the video signal to a plurality of channels, means for recording and reproducing the distributed video signals by plurality of magnetic heads, means for synchronizing a time-base correction signal for time-base correction with a sampling signal for Hadamard transformation, and means for phase-controlling a sampling signal for Hadamard inverse transformation to the time-base correction signal in phase.

Abstract: At least one bit of a digital signal including a plurality of bits to be simultaneously recorded on a plurality of tracks of a magnetic tape, is recorded on at least two tracks located at opposite sides with respect to a reference track. The reference track carries a reference signal utilized for producing a synchronous signal with which the plurality of bits are reproduced in synchronization. When reproducing, a.c. signals derived from the two corresponding tracks having the simultaneously recorded bits are added to each other whereby the phase difference of the plurality of bits with respect to the reference signal is compensated while drop out phenomenon is reduced.

Abstract: Control apparatus for a tape recorder includes a Central Processor Unit (CPU) and a Control Panel having data entry switches, mode selection switches, speed selection switches, a multiposition function select switch and other controls and a display, all of which communicate with the CPU. The system enables the operator to enter commands to be executed by the CPU in controlling the tape transport at predetermined footage locations on the tape (such as Beginning of Data or End of Data) or at a predetermined value of parameters, such as tape pack diameters of the reel being emptied or filled (Beginning of Tape or End of Tape). The operator may enter data to set or change such locations or other parameter; and he may change commands in the CPU via the data entry switches. The operator may retrieve data or command signals from the CPU and view them on a display. A footage indicator is stored and continually updated in the CPU, and it may be changed to any desired footage setting by the operator.

Abstract: In the case that an analog signal is recorded or reproduced by using a sensor and recording medium relatively moving against the sensor, a sampling signal is generated which is adapted to have a frequency thereof deviated dependently upon an amount of wow and flutter caused by fluctuations in the speed of the relative motion therebetween. A reproduced signal is sampled by means of the sampling signal and, a sampled signal is stored in a memory. After this, a stored contents in the memory are read out by using a reading signal with a predetermined frequency, thereby to remove from the reproduced signal varying frequency components caused by the wow and flutter.

Abstract: As an aid in counting servo tracks in a position servo system, a position window detector (30) which normally provides coarse and fine pulses to counting logic (53) also provides fine pulses to a reset switch (45) of a tachometer signal integrator means (33), resetting the integrator once for each track. In the event of position signal drop-out wherein coarse pulses are not properly generated, a threshold detection means (43) senses when the output of the integrator reaches a threshold level and produces a threshold reached signal which is transmitted to counting logic means (53) for incrementing a track counter (61).

Abstract: A system for recording analog information on a magnetic medium in which the record bias is dynamically varied in response to the amplitude in a predetermined frequency spectrum of the information to be recorded. The record amplifier gain and equalization may be simultaneously dynamically varied as the record bias in order to maintain a record/playback response relatively invariant with respect to changes in the bias level.

Abstract: The invention provides matching circuitry for use with a radar station and television magnetoscope, the latter having a video channel and an audio channel. The matching circuitry enables the audio channel of the magnetoscope to be used for information concerning the instantaneous position of the antenna of the radar station, and the video channel for video and synchronizing signals. An oscillator isused to supply artificial frame pulses to a control track of the video channel of the magnetoscope. The recordings of these pulses are used to synchronize the video reading head of the magnetoscope when the information is being retrieved or reproduced from the magnetoscope.

Abstract: Control apparatus for a tape recorder includes a Central Processor Unit (CPU) and a Control Panel having data entry switches, mode selection switches, speed selection switches, a multiposition function select switch and other controls and a display, all of which communicate with the CPU. The system enables the operator to enter commands to be executed by the CPU in controlling the tape transport at predetermined footage locations on the tape (such as Beginning of Data or End of Data) or at a predetermined value of parameters, such as tape pack diameters of the reel being emptied or filled (Beginning of Tape or End of Tape). The operator may enter data to set or change such locations or other parameter; and he may change commands in the CPU via the data entry switches. The operator may retrieve data or command signals from the CPU and view them on a display. A footage indicator is stored and continually updated in the CPU, and it may be changed to any desired footage setting by the operator.

Abstract: Apparatus is provided to permit the control of circuitry within a video game generator including an audio playback device employing an audio tape or phonograph disc having recorded thereon digital data which is decoded and interfaced with the video game generator.

Abstract: The invention comprises a circuit arrangement for a sound-reproducing apparatus, particularly a video tape recorder having an audio channel, wherein upon the occurence of a sound signal drop-out interval within a continuous audio signal, for example within the track-switching period in multi-track sound recordings, an audio frequency signal is inserted in the drop-out interval so that the interval is rendered unnoticeable to the listener. The apparatus can be advantageously employed for recorders in which sound signals are recorded on the tracks of a magnetic tape or disc, or on grooved tracks in a disc. In one preferred embodiment of the invention the arrangement comprises circuitry for attenuating the noise burst which occurs during the track-switching period of a multi-track recorder using a frequency modulated audio signal, the degree to which the noise is attenuated being correlated to the level of the immediately preceding audio signal.

Abstract: Apparatus for directly recording television signals on a magnetic medium strips out sync and blanking information. Low frequency components of the television signals are time compressed, i.e. frequency shifted, and recorded as a substitute for the stripped-out sync and blanking information. Thus, high frequency components of each video line are recorded, followed by that line's low frequency components, thereby facilitating the playback of low frequency information. In time compressing the low frequency information, the video signal content of a line is sampled at a predetermined rate. Each sample is then quantized for purposes of improving the playback signal-to-noise ratio, i.e. the effect of tape modulation, and other, noise is nullified by sample quantization. And, to cut the bit rate resulting from sample quantization, a preferred form of the invention groups the quantized bits and records analog representations of the bit groups.

Abstract: A method and apparatus for the recording and reproduction of an audio signal for multi-channel play-back in which both a monaural signal and a code signal are recorded on a magnetic tape, the recorded code signal having characteristics in accordance with the selective feeding of the audio signal to the various channels together with an adjusting device through which the code signal is controlled to thereby control the distribution of the audio signal throughout the multi-channel reproduction apparatus during multi-channel reproduction of the audio signal.

Abstract: A method of recording an index signal in a dictating tape recorder of the type in which a single button is utilized to switch the recorder to each of a stop, a playback, a record and a tape rewind position. The method comprises moving the button beyond the record position to close a switch which actuates an oscillator for generating an index signal. The signal output from the oscillator is applied to a record head, thereby recording the index signal on a magnetic tape.

Abstract: An information signal is compressively encoded for application to a limited amplitude transmission channel, such as a cinemagraphic film, by generating a gain control signal which represents the information signal level, delaying the information signal until the gain control signal has been substantially generated, and using the gain control signal to control encoding of the delayed information signal. The encoded information signal may be transmitted by itself with a similar delay step employed to decode it after reception, or the gain control signal may be transmitted along with the information signal and employed in the decoding operation, thereby avoiding the need for a delay step in the decoding process. In the latter case the gain control signal may be encoded along with the information signal, and employed in a feedback control loop for the encoding process.The invention also includes apparatus designed to perform the disclosed method.

Abstract: A circuit arrangement for calibrating a signal by calibrating a storage medium upon which the signal is recorded comprising circuits for producing calibration signals and for interfacing information, calibration and marking signals, a timing and control circuit for controlling periods of calibrating signals recorded on the storage medium and derived by a calibrating circuit.A circuit for providing marking of an event external to the signal is provided.

Abstract: Apparatus and method for reducing flutter noise in a frequency-modulated data stream, wherein the data stream is combined with a reference stream which has been modified by the fed-back result of the combination. Before combination, the data stream is transformed into a first rectangular-pulse stream in which amplitude is constant and frequency is dependent on the frequency of modulation of the data stream, whereas the reference stream is transformed into a second rectangular pulse stream of amplitude which is dependent on the fed-back result of the combination of the streams, and the frequency is dependent on the frequency of modulation of the reference stream.

Abstract: Method and apparatus for use with a magnetic tape playback machine to attenuate recorded audio signals relative to the super-imposed control signals while the magnetic tape is being transported past the sensing surface of a playback head. The control signals are recorded in a frequency range which is lower than the frequency range of the recorded audio signals. A spacer is attached to the sensing surface of the playback head to space the magnetic tape a preselected distance from the sensing surface and thereby attenuate the higher frequency audio signals relative the lower frequency control signals. The higher frequency attenuation obtained is independent of the frequency of the signals induced into the playback head and is thereby independent of the linear velocity of the magnetic tape as it is transported past the sensing surface of the playback head.

Abstract: A first main information signal is recorded in a first track extending longitudinally along one side of a length of magnetic tape and a corresponding first secondary, or control, signal is recorded in a narrow parallel track spaced from the first main track. A second main signal is recorded in a third track within the other half of the tape, and a corresponding second secondary, or control, signal is recorded between the first secondary signal and the first main signal, whereby the two main signals and the two secondary signals are interleaved with each other. The first and second main tracks are equal in width, and the first and second secondary tracks are also equal in width but are much narrower than the first and second main tracks.

Abstract: Apparatus for directly recording television signals on a magnetic medium strips out sync and blanking information. Low frequency components of the television signals are time-compressed, i.e., frequency shifted, and recorded as a substitute for the stripped-out sync and blanking information. Thus, high frequency components of each video line are recorded, followed by that line's low frequency components, thereby facilitating the playback of low frequency information. In a preferred form, the low frequency video information is time-compressed sufficiently to provide time, during the time slot which corresponds to sync and blanking information, for the recording of reference signal information. During playback, the reference signal information is employed to set the gain of the playback circuit.

Abstract: Unauthorized duplication of recorded audible program material upon magnetic tape, commonly known as tape piracy, is prevented and rendered detectable by the present method and apparatus for preparing the program material. The method and apparatus prepare recorded audible program material by generating a high frequency modulated signal which varies in a predetermined manner over a selected spectrum of frequencies, and by recording the modulated signal together with the audible program material so that subsequent copying of the program material and modulated signal onto magnetic tape with conventional high frequency bias will produce on the copied tape detectable and identifiable interference signals arising between the modulated signal and the conventional recording bias. The modulated signal may sweep a range of frequencies at a rate which will produce an audible playback noise spoiling the copied tape, and the modulated signal can be coded to identify the origin of the program material.