GB2118387A - Disc player - Google Patents

Abstract

An audio EM signal recovered from a disc record is demodulated to baseband by an EM demodulator 44, 46, the baseband signal tending to exhibit a low frequency transient disturbance audible upon a change in the state of the player power control switch 10. The baseband signal is coupled to a player output terminal 70, 72 via a path including a track-hold circuit 50, 52 and a variable gain amplifier 80, 82. The track- hold circuit is normally conditioned to track the baseband signal but assumes its hold operating mode when frequency excursions of the EM signal exceed predetermined limits to suppress record defects such as ticks and pops. The variable gain amplifier functions as an expander for baseband signals of compressed form and as a constant gain amplifier for baseband signals of non- compressed form. The player output signal is muted and the transient disturbance is suppressed by a control circuit 56, 58, 60, 84, 86, 88, D1 which places the track-hold circuit in its hold mode and simultaneously conditions the amplifier to function as an attenuator during selected player operating modes. <IMAGE>

Description

SPECIFICATION Disc player This invention relates to a disc player. An illustrative application of the invention is to a video disc player to which reference is made by way of example.

Video disc record formats have been proposed in which sound and picture signals are recorded on separate FM carriers and recovered by respective FM demodulators in a video disc player. Keizer, in U.S.

Patent 3,972,064 describes a player having a single sound demodulator for playing monophonic records. In U.S. Patent 3,969,756 Palmer et al. describe a player having stereophonic-bilingual capabilities and which includes a pair of sound demodulators.

It is desirable to mute the audio output signal of a video disc player under certain circumstances. In the monophonic player proposed by Pyles et al. in U.S.

Patent 4,286,290, an audio muting circuit is activated during the "PAUSE", "LOAD" and "SCAN" player operating modes to prevent noise which may be produced by the sound demodulator during such modes from reaching the player output. Pyles et al.

suggest that the audio muting be provided by means of a series or shunt switching of the demodulator output signal or by applying a squelch signal to the limiter stage of the FM demodulator as is generally known from U.S. Patent 4,017,677 of A.L. Baker. In U.S. Patents 4,119,812 of Fox and 4,221,930 of Okuno, track and hold circuits coupled to the sound demodulator outputs assume a hold operating mode when record defects are encountered to suppress ticks and pops in the audio output signals.

Track-hold circuits may be used to advantage to provide both tick and pop suppression and audio muting in a video disc player. A monophonic video disc player having such a feature is described in the publication "SFT100 Player Technical Manual" published in 1980 by RCA Corporation, Chapter V, pp.

35-38. A track-hold circuit in the player is normally operated in its tracking mode but is switched to a hold operating mode when either audio FM carrier defects are detected or when an audio muting signal is present. The muting signal is produced by the player control microprocessor during selected player operating modes other than PLAY (e.g., PAUSE, SEARCH, SCAN, LOAD, etc.) when a usable audio signal would not normally be recovered from the record. The output of the track-hold circuit is applied to a TV modulator along with a processed video signal to provide an RF output signal for use with a conventional television receiver.

The present invention is directed to a problem which may become objectionable when the audio output of a video disc player of the general kind described above is applied to a high fidelity sound system rather than to a TV receiver for reproduction.

Specifically, the generally superior low frequency response capabilities of a "hi-fi" system tends to accentuate low frequency transient disturbances of the audio signal. The track-hold form of muting arrangement, notwithstanding its advantages, has not been found to be entirely satisfactory for muting a particular form of transient referred to herein as a "turn-on" or "turn-off" transient. Such transients, as the name implies, may be produced by the player sound demodulation circuits when the player operating power is turned on or off and typically may be of an amplitude substantially greater than the normal audio signal level and may exceed the track-hold circuit dynamic range.

The problem of turn-on orturn-offtransients becomes even more acute in players where additional processing (e.g., amplification, stereo signal decoding, or expansion) is performed subsequent to demodulation. The additional processing circuits, particularly those including amplifiers, may tend to exaggerate turn-on or turn-off transients produced by the demodulation circuits and thus place unrealistically high attenuation requirements on the audio muting circuits.

The present invention is directed to meeting the need for a disc player having improved immunity to turn-on and turn-off transients.

A disc player embodying the invention includes a variable gain amplifier means conditioned to function as a signal expander or as a fixed gain amplifier in one operating condition of the player and as an attenuator during selected other operating conditions of the player.

The invention is illustrated in the sole Figure which is a block diagram, partially in schematic form, of a video disc player embodying the invention.

The player is intended for use with several types of video disc records. One type is that in which monaural program material is recorded on a single FM carrier. Another type is that in which stereophonic material is recorded in matrixed form with the L+R stereo sum signal on one FM carrier and the L-R stereo difference signal on another FM carrier.

A third type of record is that in which bilingual material is recorded in unmatrixed form with each language or program being recorded on a respective FM carrier. Such a recording format has the advantage of being compatable with existing monophonic video disc players as explained in detail in British Patent Application 2096435A corresponding to U.S.

Patent application entitled "VIDEO DISC PLAYER FOR MONOPHONIC, STEREOPHONIC AND BILING UAL RECORDS", Serial No. 248,776 filed March 30, 1981. Additionally, it will be assumed that for stereophonic records the sum and difference signals are compressed prior to application to the recording frequency modulator circuits during mastering of the disc. This provides a desirable signal-to-noise ratio improvement in the player when the demodulated stereo signals are subsequently decoded and expanded in the player as explained in British Patent Application 2095955A corresponding to U.S. Patent application entitled "VIDEO DISC PLAYER WITH SELECTIVELY ENABLED AUDIO SIGNAL EXPANDER CIRCUITRY", Serial No. 244,665 filed March 17,1981.

The player comprises a power supply (on/off) switch 10 for controlling the supply of AC power (AC in) to a power supply unit 12 that provides DC operating voltages (DC out) to the player processing circuits. A playback unit 14 includes a turntable for rotating a video disc record 18 and a pick-up transducer 20 for recovering recorded information from the record. Illustratively, it will be assumed that the player is intended for use with records of the type in which information is stored in the form of topological variations and recovered by sensing capacitance variations between pickup transducer 20 and the record 18. (Alternatively, the record and transducer may be of the optical type). It will also be assumed that audio signals are recorded in the format previously described.

The output of transducer 20 is coupled to the input of a pickup converter 22 responsive to capacitance variations between a stylus in transducer 20 and the record being played for providing an FM output signal representative of the recorded information inclusive of picture and sound carrier waves. Records of the capacitance storage type and suitable circuits for providing the capacitance-to-voltage conversion function of converter 22 are well known. See, for example, U.S. Patent 3,783,196 "High Density Capacitive Information Records and PlaybackApparatus Therefore" of T.O. Stanley, "Apparatus and Methods for Playback of Color Pictures/Sound Records" of E.O. Keizer and U.S. Patent 3,711,641 "Velocity Adjusting System" of R.C. Palmer.

The FM output signal of converter 22 is applied to the input of a video processor 24 which includes a picture frequency bandpass filter, demodulator and conversion circuitry for providing a baseband video output signal of a standard television format such as NTSC or PAL. Such processors are known, see for example, U.S. Patent 4,247,866 of T.J. Christopher and J.A. Wilberwhich describes a suitable NTSC standard processor and U.S. Patent 4,314,273 of J.G.

Amery which describes a PAL standard processor.

The audio portion of the FM signal is processed as will be explained and applied along with the processed video signal to the inputs of a TV modulator 26 which supplies an RF output signal (inclusive of picture and sound components) to an RF output terminal 28 for connection to the antenna terminal of a conventional television receiver. An integrated circuit suitable for use as TV modulator 26 and which may be selectively operated to provide an output signal on selected TV channels (e.g., Channels 3 or 4) is the model LM 1889N "TV Video Modulator" made by National Semiconductor Company, Inc.

A control unit 30 (preferably microprocessor based as opposed to the alternative of being implemented with random logic) coupled to playback unit 14 and processor 24 provides various control functions including, illustratively, control of the radial position, elevation and direction of movement of pickup transducer 20 relative to disc 18 and squelching of the video output signal of processor 24. The squelch signal (SQ) and audio muting signal (AM) produced by controller 30 are also supplied to terminals SQ and AM of the player audio processing circuits.

A player control switch unit 32 is coupled to an input of controller 30 and includes user activated switches for initiating player operating mode functions such as play, pause, scan, etc. Upon closure of one of the user activated switches in unit 32, controller 30 addresses its internal read only memory (ROM) and fetches an appropriate sequence of instructions resident in the memory for effecting the desired control function. For example, in the pause or rapid scan modes, controller 30 produces the video squelch SO and audio muting AM signals and also supplies a stylus lift signal to transducer 20. The audio muting signal (active low, as indicated) is produced in all player operating modes otherthan the play operating mode (e.g., AM is low during the load, pause, slow scan and rapid scan modes).

Controller 30 also supplies track error correction signals to transducer 20 generated from field identification data signals recovered from the video FM signal by processor 24. Controller 30 may be of the kind described in U.S. Patent 4,308,577 "VIDEO DISC SYSTEM" of C.B. Dieterich and may be interfaced with processing unit 24 as described in C.B. Dieterich's U.S. Patent 4,275,416 "PCM DETECTOR" which issued June 23,1981.

Baseband audio signals S1 and S2 are recovered from disc 18 by applying the output of converter 22 to a pair of FM demodulators 44 and 46 via respective bandpass filters 40 and 42. Preferably, the sound carrier center frequency choices correspond to odd multiples of half the line frequency as proposed in U.S. Patent 3,969,756 of Palmer et al.

Illustratively, for NTSC standard players, filters 40 and 42 may have center frequencies of 715 KHz and 905 KHz, respectively, and bandwidths somewhat wider than the sound carrier peak deviation so as to ensure passage of first order and second order sideband components of the modulated sound carriers.

Demodulators 44 and 46 also include defect detectors for providing respective defect indicating signals S3 and S4 (active low pulses, as indicated) in response to departures of a parameter (e.g., phase or amplitude) of the FM signal beyond normal limits.

Suitable demodulators are described, for example, in U.S. Patent 4,203,134 of T.J. Ch ristopher "FM SIGNAL DEMODULATOR WITH DEFECT DETEC TION" and U.S. Patent 4,038,686 of A.L. Baker "DEFECT DETECTION AND COMPENSATION".

The baseband audio signals S1 and S2 are applied via respective track-hold circuits 50 and 52 to the inputs of a stereo decoder 54. Circuits 50 and 52 may be of the series switch-shunt capacitor kind which provide an output signal which equals or "tracks" the input signal when the switch is closed and which remains at the last value of the input signal when the switch is opened and, as will be explained, provide the triple functions of defect (tick and pop) suppression, channel selection and audio muting. The switch in each circuit may be a field effect transistor, a preferred switch being a transmission gate such as the type CD401 6 integrated circuit (which contains four CMOS transmission gates). A high level input closes the transmission gate and a low level input opens the gate.

Circuits 50 and 52 are normally maintained in the tracking mode by high level output signals provided by AND gates 56 and 58, respectively. Gate 56 has inputs coupled to receive the defect indicating signal S3, the audio muting signal AM and a channel disable signal S5 and produces a low level signal which places circuit 50 in its hold operating mode when any one or more of these signals (all active low) is present. Gate 58 controls circuit 52 in a similar manner in response to the defect signal S4, the audio muting signal AM and a channel disable signal S6. The channel disabling signals S5 and S6 are provided by the first section of a two pole three position channel selector switch 60.In position "1 " signal S6 is coupled to ground, thereby muting signal S2 and in position "2" signal S5 is coupled to ground, thereby muting signal S1 and in position "3" (the stereo position) neither signal is grounded.

(Pull-up resistors, not shown, may be coupled to contacts 1 and 2 to assure the signals S5 and S6 are at high logic levels when switch 60 is in the stereo position 3).

The channel two processor (CH-2) differs from the channel one (CH-1) processor in that it includes a loss-of-carrier detector for automatically muting signal S2 in the absence of the 905 KHz sound carrier. The loss-of-carrier detector comprises a low pass filter 62 which "integrates" or smoothes the defect pulses S4. An inverter (not shown) may be used to provide positive defect pulses to filter 62 so that the filter output is porportional to the number of defect pulses or the defect pulse rate. In the absence of the 905 KHz carrier, the defect pulse rate will be high, thereby producing a high output voltage at the output of filter 62 which is detected by detector 64 to produce the loss-of-carrier signal S7 (active low).

This signal is applied to an inhibitable amplifier in demodulator 46 which mutes signal S2 and also to an inhibit gate 66 in the defect pulse path to gate 58 which inhibits the defect pulses 54 to thereby prevent random activation of gate 58 which might otherwise produce undesirable noise in track-hold circuit 52. A suitable inihibitable amplifier for use in demodulator 46 is described in U.S. Patent 4,257,009 "INHIBIT CIRCUIT FOR A DIFFERENTIAL AMPLIFIER" which issued to B.J. Yorkanis March 17, 1981.

The signals S1, S2 and S5 are applied to the inputs of a dual mode stereo decoder matrix which provides audio output signals S8, S9 and S10 to TV modulator 26, audio output terminal 70 and audio output terminal 72, respectively. Terminals 70 and 72 are provided for connection to the right (R) and left (L) input terminals of a user stereo sound system.

Decoder 54 may be of the kind described in the previously mentioned GB-A-2096435 (U.S. Patent Application Serial No. 248,776 filed March 30,1981) and provides the following functions when matrixed stereophonic and un-matrixed monophonic or bilingual records are being played. First, format rixed stereophonic signals, signals S1 and S2 correspond to the stereo sum (L+R) and difference (L-R) signals, respectively. With switch 60 in the stereo position (3) signal S5 is high and decoder 54 adds S1 to S2 to produce the left channel output signal S10, subtracts S2 from S1 to produce the right channel output signal S9 and adds S9 to S10 to produce the L+R monophonic output signal S8 for TV modulator 26.For monophonic or channel one (CH-1) bilingual signals (unmatrixed), switch 60 is placed in position 1 which mutes signal S2 as previously explained and signal S is coupled to the S8, S9 and S10 signal outputs of decoder 54. To playback channel two of a bilingual record switch 60 is placed in position 2 which mutes signal S1 and simultaneously disables the signal subtraction circuitry in decoder 54 whereupon signal S2 is coupled to the S8, S9, and S10 decoder signal outputs. (The subtraction circuit is disabled in decoder 54 for channel two playback to prevent signals S9 and S10 from being out-of-phase which otherwise would tend to cancel signal S8 and produce out-of-phase acoustic fields in the user's stereo system as explained in detail in the previously mentioned patent application).

It is desirable for purposes of signal-to-noise ratio enhancement that stereo signals be compressed during recording and expanded upon playback as previously explained. This has been not necessary for monophonic or bilingual signals. The remaining portion of the video disc player provides the triple function of: (1) expanding compressed signals; (2) amplifying uncompressed signals with constant gain; and (3) muting the player output during selected operating modes for suppressing low frequency high amplitude baseband transients of signals S9 and S10 which may be produced when the position of the player power switch 10 is changed (e.g., from off to on or vice versa).

In more detail, the signals S9 and S10 are coupled to player output terminals 70 and 72 by respective variable gain amplifiers 80 and 82. A gain control signal S11 is applied in common to the gain control terminals of amplifiers 80 and 82 via a path including a multi-time constant dynamic filter 84 which may be of the type described, for example, in the U.S. Patent Application of T.J. Christopher and G.N. Mehrotra "SIGNAL EXPANDER" Serial No. 229,743 filed Janu arty29,1981 orin British Patent Application 2094594A corresponding to the U.S. Patent Application of C.B. Dieterich "SIGNAL EXPANDER WITH ADAPTIVE CONTROL CIRCUIT" Serial Number 229,518 filed January 1981.As explained in detail in the above applications, the smoothing time constants of filter 84 change or adapt to dynamic changes of the control signal S11 so as to reduce audibility of abrupt gain changes. The variable gain amplifiers may be in the form of an integrated circuit such as the type LM 13,700 integrated circuitwhich exhibits a gain proportional to the value of bias current supplied to its gain control terminal. When such a current controlled variable gain amplifier is used in the player, the output of filter 84 should be suitably conditioned to exhibit a high output impedance. This may be done by coupling filter 84 to amplifiers 80 and 82 via a voltage-to-current converter, such devices being well known in the art.

The gain control signal S11 is selectively obtained from three different sources in the player depending on the player operating condition. One source comprises a detector 86 which rectifies the signals S9 and S10 and supplies the resultant rectified signal to a resistance-capacitance (RC) low pass filter comprising resistor R1 and capacitor C1 which provides a smoothed output voltage which varies as a function of the amplitude of signals S9 and S10.

This variable voltage is used to bias amplifiers 80 and 82 to expand the player output signals. Suitable values for R1 and C1 are 3000 Ohms and 0.33 microfarad, respectively. Another source of control signal S11 is a potential divider comprising resistors R2 and R3 coupled between a supply voltage source (+V) and ground and having an output tap coupled to filter 84 via a transmission gate 88. The resistor values are selected such that the tap voltage is sufficient (after passing through filter 84) to bias amplifiers 80 and 82 to provide constant (non-zero) amplification of signals S9 and S1 O. The third source of signal S11 comprises audio muting terminal AM which is coupled to ground via a capacitor C2 and coupled via a diode D1 and transmission gate 88 to the input of filter 84.Diode D1 may, alternatively, be connected directly to the input of filter 84 (as indicated by the dashed alternate path). The audio muting signal AM in this example of the invention is normally high and assumes a low level (e.g., ground) when audio muting is desired. Diode D1 is poled to block the audio muting signal from filter 84 when playing a record. When the audio muting signal is present, diode D1 becomes forward biased and clamps the input of filter 84 to ground, thereby causing amplifiers 80 and 82 to attenuate the player output signal. Any transients which may accompany the output signal are also attenuated.Capacitor C2 is relatively large (e.g., 10 microFarads or so) as compared with capacitor C1 and provides the dual functions of smoothing signal AM and delaying turn-off of signal AM. Additional smoothing is provided by filter 84 so that the rate of change of the gain of amplifiers 80 and 82 due to the audio muting is relatively limited, thereby preventing transients from being induced in the player output signal when signal AM changes states. The delay in restoration of gain provided by capacitor C2 further ensures that transients produced at the output of demodulator 44 and 46 have sufficient time to settle (e.g., 200 milliseconds or so) as play resumes and the audio muting signal terminates.

Transmission gate 88 provides the functiion of selecting which of the three sources of control signals S11 controls the variable gain amplifiers 80 and 82. In the stereo mode, gate 88 is open whereby signal S11 varies as a function of the amplitudes of the compressed signals S9 and S1 O to variably expand the player output signal. In the monophonic or bilingual mode, gate 88 is closed and signal S11 is maintained at a constant level determined by resistors R2 and R3 so amplifiers 80 and 82 function as fixed gain amplifiers for the non-compressed S9 and S10 signals.During all modes except "PLAY" gate 88 is closed and diode D1 is switched on in response to the audio muting signal AM whereby signal S11 assumes a ground level thereby causing amplifiers 80 and 82 to attenuate the player output signal and any transients which may be produced by demodulators 44 or46 in response to opening or closing of the player power switch 10.

Control of transmission gate 88 is provided by a common emitter connected NPN transistor Q1 having a collector electrode connected to the control input of gate 88 and via a parallel circuit to a source of supply voltage +V. The parallel circuit includes a collector pull-up or load resistor 90 connected in parallel with a series circuit comprising a stereo indicator light emitting diode (LED) 92 and a current limiting resistor 94. Turn-on of transistor Q1 lights the LED stereo indicator and applies a low voltage to transmission gate 88, thereby turning gate 88 off and causing signal Sil to vary as a function of signals S9 and S10 thereby variably expanding the player audio output signals.

Transistor Q1 normally receives turn-on base current via another NPN transistor Q2 having a collector emitter path coupled in series with a current limiting resistor 96 between the +V supply and the base of Qi Transistor Q2 is normally biased on by the loss of carrier signal S7 (normally high, low when carrier is absent) that is applied to the Q2 base via current limiting resistor 98. The base of Q1 is also connected to contacts 1 and 2 of the second section of selector switch 60, the pole of which is grounded. Resistor 98 is also coupled to terminal SQ via a diode D2.With this switching arrangement, transmission gate 88 will be closed and stereo indicator 92 will be extinguished if any one of three conditions exist, namely: (1) loss of carrier signal S7 present, (2) switch 60 in a non-stereo position (1 or2) or (3) video squelch signal SQ (active low) present.

As a further illustration of operation of the player, assume that power switch 10 is closed, that audio channel selector switch 60 is in the stereo position (3) as shown and that a stereo record is being played. Under these conditions, the loss-of-carrier signal S7, the video squelch SO and audio muting AM signals will all be high, transistors Q1 and Q2 will be on, the stereo indicator LED 97 will be illuminated and amplifiers 80 and 82 will variably expand the compressed baseband stereo signals S9 and S10. If defects are present in the audio carriers, the defect pulses S3 and S4 will mute signals S1 and S2 respectively by placing track-hold circuits 50 and 52 in the hold mode of operation. If the player is placed in the pause mode of operation, signals S7, AM and SO will assume a low state.Signals S7 and SO will both extinguish the stereo LED 92 and close gate 88.

At the same time, signal AM will doubly mute the audio signals by (1) placing circuits 50 and 52 in the hold mode and (2) grounding the input of filter 84.

Any transient which may be produced by demodulators 44 or 46 and which tends to "feed trough" circuits 50 or 52 will ultimately be completely suppressed by variable gain amplifiers 80 and 82 which are biased to serve as attenuators when diode D1 is conductive (signal AM present). The operation is similar when playing bilingual or monophonic records except that switch 60 is placed in the non-stereo position to select the desired channel 1 or 2 so that gate 88 is closed and amplifiers 80 and 82 serve as fixed gain amplifiers for the noncompressed signals. In this mode, the audio muting signal provides the same function in the OFF, LOAD, PAUSE, SCAN, etc. player operating modes of biasing amplifiers 80 and 82 to serve as transient suppressors (attenuators).

Capacitor C2, as previously noted, provides the functions of smoothing and delaying termination of the audio muting signal. Some smoothing is also provided by filter 84. As a result, the audio muting signal does not abruptly change the gain of ampli fiers 80 and 82 thereby minimizing the possibility of gain change induced transients in the player audio output signals. Capacitor C2 is normally in a discharged state when the player is off. At turn-on, the discharged state assures that diode D1 will initially be forward biased and amplifiers 80 and 82 will therefore initially be in the attenuation mode thereby suppressing turn-on transients produced by powerup of the player processing circuits when switch 10 is closed (signal AM is also low at that time).

The reason for delaying termination of the audio muting signal at turn-on is to allow sufficient time for the audio processing circuits to reach a steady state operating condition (time is required for amplifiers to stabilize after the DC power is first applied).

Capacitor C2, being relatively large, provides this delay in termination of the audio muting signal. It is not necessary, however, that a capacitor be used for this purpose as the delay may be produced by the microprocessor control unit if desired by suitable programming. (Delay programs are well known in the microprocessor art). Since filter 84 provides smoothing of the AM signal and delayed termination of the AM signal may be provided by the control microprocessor, one may omit capacitor C2 from the player if desired. It should be noted further that if signals S9 and/or S10 include turn-on transients, any tendency for capacitor C1 to charge will be counteracted by capacitor C2 and the low state of audio muting signal AM.

Claims (12)

1. A disc player, comprising: a power switch having on and off states for controlling the supply of operating power to said player; signal recovery means for playing a disc record and providing at least one FM sound carrier signal; demodulator means for demodulating said FM sound carrier signal to provide a baseband signal, said baseband signal tending to exhibit a transient disturbance upon a change in the state of said power switch; variable gain amplifier means having an input for receiving said baseband signal, an output for providing a player output signal; and gain control means having a first operating mode for varying the gain of said amplifier means as a function of the amplitude of said baseband audio signal, a second operating mode for maintaining the gain of said amplifier means at a substantially constant non-zero level and a third operating mode for reducing the gain of said amplifier means to a level sufficient to attenuate said player output signal and suppress said transient disturbance.

2. A disc player as recited in Claim 1 wherein said gain control means includes: a source for providing an audio muting signal during selected operating modes of said player; and a circuit path for coupling said audio muting signal to a gain control terminal of said amplifier means.

3. A disc player as recited in Claim 2 wherein said gain control means further comprises: means operatively associated with said circuit path for effectively smoothing said audio muting signal prior to application thereof to said gain control terminal of said amplifier means.

4. A disc player as recited in Claim 2 further comprising: means in said player for effectively delaying termination of said audio muting signal for a predetermined length of time.

5. A disc player as recited in Claim 4 wherein said means for effectively delaying termination of said audio signal comprises an energy storage element coupled to a selected point in said circuit path.

6. A disc player as recited in Claim 2 wherein said source for providing said audio muting signal comprises a microprocessor having input means for receiving an operating mode control signal manifestation and an output for producing said audio muting signal during player operating modes other than a PLAY mode, said microprocessor being conditioned to delay termination of said audio muting signal for a predetermined length of time subsequent to the start of said PLAY operating mode of said player.

7. A disc player as recited in Claim 1 further comprising: track-hold circuit means for coupling said baseband signal to said input of said variable gain amplifier means; means for placing said track-hold circuit means in a hold operating mode in response to departures of a parameter of said FM signal beyond predetermined limits; and means for placing said track-hold circuit means in said hold operating mode when said gain control means is in said third operating mode.

8. A disc player as recited in Claim 7 wherein said gain control means comprises: a source for providing an audio muting signal during selected operating modes of said player; and a circuit path including filter means for coupling said audio muting signal to a gain control terminal of said amplifier means.

9. A disc player as recited in Claim 1 further comprising a source for providing an audio muting signal during selected player operating modes and wherein said gain control means comprises: first means for producing a smoothed control signal which varies as a function of the amplitude of said baseband audio signal; second means for producing a substantially constant control signal; and circuit means for selectively applying said smoothed control signal, said constant control signal and said audio muting signal to a gain control input of said amplifier means.

10. A disc player as recited in Claim 9 further comprising a circuit path for coupling the selectively applied signal to said gain control input of said amplifier means and filter means having a plurality of time constants interposed in said circuit path.

11. A video disc player according to any preceding claim.

12. A video disc player substantially as hereinbefore described with reference to the Figure.