NO862029L - GRAMPHONE PLATE SYSTEM. - Google Patents

Description

The invention relates to a method and a device

for reproduction of mechanical records having modulated and unmodulated parts.

Commercially produced gramophone records exhibit various mechanical imperfections, and further system imperfections arise from the mechanical devices used to reproduce the record. The present invention deals with one category of imperfections in disc playback systems, namely false vertical deviations of the disc groove, mainly as a result of disc windage and rumble, including disc imprint noise. Such imperfections can cause significant deterioration of the reproduced signal.

Windward bias or throw

A general discussion of plate wind bias is contained

in the following published paper: "Record Warps and System Playback Performance", by Larry Happ and Frank Karlov, Journal of

the Audio Engineering Society, Vol. 24, No. 8, October 1976, pages 630 - 638. The authors found wind skew or throw frequencies in the range from approx. 1/2 Hz (the one-shot orbital frequency at 33 1/3 rpm) to over 10 Hz, with 95% of the throws below 8 Hz. The greatest physical amplitude height of the throws was greatest at low frequencies at approx. 0.64 mm maximum and decreased with increasing frequency.

Various problems are caused by record windage skew: The pickup arm can bounce or wobble relative to the record surface due to the vertical and, to some extent, lateral forces caused as the pin tries to follow the varying record height. This can cause not only variations in tracking or groove following force, but also bottoming of the pickup head or complete loss of contact between the pin and the grooves. Such variations in tracking power from the optimum will often affect the reproduced signal at audible frequencies. In addition to causing pin and arm tracking problems, large pin runs result in geometrically related distortions and electromechanical nonlinearity of the pickup head. In addition, inaudible spurious signals can cause amplifier overload distortion in electronic systems that pass such low frequencies and, if fed into the speaker system, can cause significant woofer movement that can result in extraneous noise and distortion of higher frequency audible signals, including Doppler -distortion. Furthermore, the geometric relationship between the pin and the disc groove is such that a wind bias or throw results in a forward and backward oscillation of the pin tip over the recorded groove information, which frequency modulates (accelerates and delays) the reproduced signal and causes a so-called "wow" . Wow can also be written from variations in rotation speed when the pin load on the disc groove varies.

The requirement to satisfactorily follow the groove in windward gramophone records has, in previously known systems, resulted in the necessity of studying the pickup arm/head/pin/plate geometry very carefully and trying to find the best combination, usually a compromise, of such factors as pin and pickup arm mass, pickup arm damping, pin compliance and damping, and tracking force, so as to provide a controlled pickup arm resonance above the typically encountered throw frequencies, yet below the frequency of the lowest recorded groove information. An arm resonance of 10 Hz has been advocated by several designers: Keisuka Ikegami and Susumu Hoshimi, "Advance in Turntable and Tone-Arm Design", Journal of the Audio Engineering Society, May 1976, Vol. 24, No. 4, pages 276 - 280, and Peter Rother, "The Aspects of Low-Inertia Tone-Arm Design", Journal of the Audio Engineering Society, September 1977, Vol. 25, No. 9, pages 550 - 559.

Although a correct choice of pickup arm and pickup head parameters can in principle enable groove tracking of wind-skewed gramophone records, the adaptation of pickup arms and heads is often complicated in practice due to the great variation in available pickup arms and heads. Even at the design stage, the further selection of optimal pickup arm and head parameters for throw tracking may not be optimal for tracking groove information with higher frequencies. Even when the plate groove is correctly followed or tracked, the problem of geometric wow and motor wow due to windage bias still remains.

Various passive devices for groove following or tracking of wind-skewed gramophone records are previously known. These devices typically use an element that moves on the surface of the plate and is attached or connected to the pickup head or the pickup arm near the head. Such devices include both damped elements and undamped or fixed elements. Examples of prior art damped element devices are shown in U.S. Patents 2,572,712 to Fisher (spring-loaded pressure piston), and 2,328,862 to Thompson (elastically mounted auxiliary pin). Fixed element devices are shown in U.S. Patents 3,228,700 to Andrews et al (felt pad at end of pickup arm with pickup head rotatable in arm) and 3,830,505 to Rabinow (air bearing near pickup head). It is also known to use a damper or a brush near the pickup head to dampen oscillations and assist in tracking wind biases. There are also known proposals for a relatively rigid element that connects the pickup arm to the plate's surface. It has also been proposed to clamp or weight the plate at its circumference and/or center to eliminate wind bias.

A previously known active system for treating record wind distortion is described in the following paper: "Overcoming Record Warps and Low-Frequency Turntable Rumble in Phonographs", by Kenneth Clunis and Michael J. Kelly, Journal of the Audio Engineering Society, July/August 1975, Vol. 23, No. 6, pages 450 - 4 58. In this system, the pickup head output is used to servo control the vertical arm position to assist in the tracking of plate wind skew. Similar systems are shown in US Patents 3,623,734 (Sakamoto et al) and 3,830,505 (Rabinow). It is also known to provide a closed loop around only the pickup arm movements to improve arm/head damping. Various aspects of the present invention can substantially improve the performance of these previously known pickup arm systems.

Rumble

Turntable rumble can come from turntable bearings, motor drive systems and ambient vibrations. Considerable efforts are made by platetal lark manufacturers to eliminate noise from these sources.

Other turntable-related disturbances are caused by acoustic feedback (sonic and infrasonic) from the speakers, whereby the turntable and/or the record can act as a recorder for the vibrations, resulting in tone coloring or even howling. Devices for reducing these effects include liquid-filled turntable mats as shown in US Patent 3,997,174 (Kawashima), and flexible turntable support bowls as shown in US Patent 4,054,291 (Maeda), both for providing a compliant or compliant damped support. under wind-skewed plates.

Despite these efforts, the main source of low frequency annoyance is plate imprint rumble or mold grain noise from the plate itself. The spectrum of record imprint noise is discussed by John Eargle in the article "Performance Characteristics of the Commercial Stereo Dise", Journal of the Audio Engineering Society, August 1969, Vol. 17, No. 4, pages 416 - 422. Mold grain noise can generally range into several hundred Hz.

Disc imprint rumble and turntable rumble are traditionally reduced by means of high-pass filters in the signal paths. Optimal pickup arm/head resonance characteristics are also useful in reducing low-frequency rumble effects.

Previously known methods for treating wind distortion are primarily aimed at the wind distortion or toss symptoms.

For example, the passive pickup arm-to-plate surface contact devices and the closed-loop pickup arm systerns act primarily as devices to increase the ability of the pickup head and pickup arm to simply follow wind biases. Such methods may consequently fail to correct other effects of wind bias, and may impair tracking capability and signal quality at frequencies without wind bias or throw. As far as rumble is concerned, the previously known methods have mainly been aimed at electrical filtering rather than dealing with the rumble mechanism itself.

It is an object of the invention to reduce the effects of wind bias and noise without in any way degrading the bandwidth or other performance characteristics of the signal channels themselves.

The invention is based on observations taken from the situation shown in fig. 1A and fig. IB. Fig. 1A represents a sectional side view of the upper half of a hypothetical mother board on which mute or silent grooves have been recorded. The groove depth a is constant and represents the instantaneous, vertical signal modulation in relation to a perfect reference path or reference surface. The reference surface can be the flat surface of the lacquer mother plate, but in accordance with one in fig. 2 shown side of the invention, the reference surface can optionally be defined in the cutting process, preferably by means of a flat, secondary cutting needle that follows the main cutting needle and is designed to smooth and dimensionally define the field or land between the grooves. In some cases, in the frequency range where little vertical information is recorded on the disc (e.g. below 30 Hz), the groove itself can be used as a reference track.

Fig. 1B represents the situation after the production of a plate reproduction of the mother plate. The vertical groove position is no longer constant, but contains irregularities. In the case of windage, these irregularities are dimensionally correlated on the two sides of the plate (thickness remains essentially constant), as they simply arise from heat and handling-related deformations during and after removal of the plate from the press. Mold grain noise with higher frequencies is not correlated on the two sides of the plate, however, as different dies and punches are used. The plate thus contains local thickness variations. Such imperfections are caused by the pressure transfer of dimensional irregularities from the back to the face of the punch or embosser during the pressing operation. Back-side surface irregularities can include metal crystals that etch from the copying process, patterns that etch from grinding operations to polish the back surface, dirt and dust trapped between the embosser and die in the plate press, and surface irregularities of the die.

Since the embossing thickness is approx. 0.18 - 0.25 mm, the stiffness of the material will limit the shortest wavelengths that can be transmitted by localized bending and deformation of the embosser. Such wavelengths can thus be of the order of 0.5 mm. This results in a highest frequency of mold grain noise at the outer diameter of a 30.5 cm plate (groove speed of about 50 cm per sec.) of the order of 1 kHz.

Further sources of low-frequency noise on the plate itself may include inhomogeneity of the plate material and geometric deformations due to differential cooling effects resulting from rapid and uneven temperature changes in the sink surface. As discussed above, noise is also caused by the reproduction system, namely turntable and ambient rumble and acoustically transmitted vibrations of the turntable and disc.

In a conventional reproduction system, the reproduced size b is thus obtained, the pickup arm position being used as a reference. The size b thus contains unwanted low-frequency noise components.

A closer examination of these questions shows that the low-frequency noise components from all the above-mentioned sources are not inextricably linked with the original signal modulations. The recorded signal size a instead remains untouched and undamaged by the pressing and rendering process and by mechanical imperfections in the rendering system. The size a can thus be recovered if the deformed reference path at the point of pin contact is used as a reference point during rendering. The rendering system preferably works to remove spurious deviations of the reference point, so that the plate surface is again effectively flat (ie effectively vertically stable) in the vicinity of the pin. Alternatively, the undulating reference point is used to determine the true signal magnitude a.

Thus, in accordance with the technique of the present invention, the problems of the prior art are solved by means of a disc reproduction system in which mechanical imperfections in the disc or in the system, which cause deviations in the tracked disc path, are compensated for by measuring a suitable size for producing an error signal, and by means of utilization of this signal to effect suitable correction, mechanically and/or electrically. A sensing device generates a signal responsive to deviations in a reference path at or in close proximity to the pickup head or pin, and this signal is processed to control the system to minimize the effect on the disc playback signal caused by the deviations.

In connection with the invention, sensing "in the immediate vicinity" means sensing within a small fraction (eg less than about one tenth) of the shortest wavelength that one wishes to correct. If shaped grain noise has wavelengths as short as approx. 0.5 mm, this means sensing within approx. 0.05 mm - i.e. on an immediately adjacent land area. This would represent the limit of the technology according to the invention. For noise and wind distortion with lower frequencies, it is of course unnecessary to sense in such close proximity.

There are four main embodiments of the invention which, for the sake of convenience, can be referred to as a vertical noise compensator (VSK). The versions can be used separately or in combination with each other.

In all embodiments, the vertical position of an unmodulated part of the plate is sensed at or in the immediate vicinity of the pin. The thus derived information can be referred to as reference path or reference track information. In some embodiments, the reference track information is sensed relative to the pickup arm or pickup head position. Such information can be referred to as reference track arm information. Reference track information or reference track arm information is preferably obtained via a sensing device which is arranged to sense the land position near the signal groove and in the immediate vicinity of the signal pin. It is essential that the vertical sensor mainly reacts only to vertical information. In disc recording technology, the term "vertical" conventionally means perpendicular to the surface of the disc, or in an axial direction. A less desirable alternative, for treating only the effects of wind bias and very low frequency rumble, is to sense the groove depth itself.

In the first embodiment, reference track information is obtained and used in a closed-loop servo system containing a drive mechanism or actuator that moves the platen generally vertically, at least in the vicinity of the pickup pin. Ideally, the result is that at least all vertical plate movement in the vicinity of the pickup pin is removed, thereby effectively allowing the pin to follow the groove of a throw-free and rattle-free record. This design can be referred to as a plate-VSK (or a plate-plate VSK, provided that vertical influence of the plate is most easily achieved via mechanisms connected to the plate).

A second embodiment, which can be referred to as a pickup arm VSK, constitutes an improvement over the previously known closed loop pickup arm methods. In the previously known systems, the error signals used contain pickup arm/pickup head resonance components or other misleading information. In the present invention, measurements which avoid these shortcomings are carried out and processed to control the pickup arm. More specifically, reference track information is obtained and used to control the pickup arm and optionally to perform additional corrections in the other embodiments. Low-frequency components can be used in a turntable VSK for throw compensation, and higher-frequency components can be used in a pickup head VSK or preamplifier VSK for rumble and shape grain noise reduction.

In a third embodiment, which may be referred to as a pickup head VSK, reference track or reference track arm information is provided and used to effect correction within or after the pickup head. The reference path arm information is canceled either electrically or mechanically from the information provided by the signal pin. The reference track arm information can optionally be brought out by the pickup head to perform further corrections via the other embodiments.

In a fourth embodiment, which can be referred to as a preamplifier VSK, the reference path arm information is provided and removed from the audio output signal electronically in the preamplifier. This arrangement can be used to reduce mould-grain noise, rumble and some of the effects of windage.

For optimal mechanical and acoustic performance, it is preferred to combine the turntable VSK or pickup arm VSK methods with the pickup head VSK and/or preamplifier VSK methods. For example, the throw and rumble effects can be compensated up to e.g.

20 Hz when using a turntable VSK or a pickup arm

VSK, as frequencies above this are processed using a pickup head VSK or preamplifier VSK.

Compatibility characterizes all embodiments according to the invention. Conventional records can be played on reproducers incorporating the invention. Conversely, discs produced with the optional specified reference surface according to the invention can be played on conventional reproducers.

The reduction of noise and tracking problems caused by the invention may allow the use of a lower modulation level and a higher groove density, leading to longer playing times and/or smaller disc diameters.

The fact that the invention solves the problem of low-frequency noise leads to the further possibility that higher-frequency components of the signal can be set on the disc in electronically noise-reducing, coded form, e.g. using the system known as "Dolby B". This system, which processes only the signals above approx. 1 kHz, produces a compressed signal that has a proven history of being sufficiently compatible to allow the sole stock manufacture and distribution of cassette tapes. Such acceptance in the case of coded discs would be more difficult, if not impossible, to achieve on a commercial basis if it was necessary to process also the low-frequency signals. The coded discs would of course preferably be played using a noise reduction decoder to reduce high-frequency disc imprint noise and low-level clicks and bangs.

The present invention can thus make a significant overall contribution to the current performance and to future possibilities of the conventional, analogue gramophone record system.

The features that characterize the invention appear from the subsequent patent claims.

The invention shall be described in more detail in the following in connection with exemplary embodiments with reference to the drawings, where fig. 1A shows a sectional side view of the upper half of a hypothetical mother plate on which silent grooves have been recorded, FIG. 1B shows a sectional side view of a hypothetical plate formed from the parent plate of fig. IA,

fig. 2 shows a partially cut side view of a mother plate

during the cutting process, where a conventional signal cutting needle and a secondary reference plane cutting needle are used in accordance with one side of the invention, fig. 3A shows a generalized representation in partial block diagram form of direct reference path information sensing in accordance with one aspect of the invention, FIG. 3B shows a generalized representation in partial block diagram form of indirect reference path information sensing in accordance with a further aspect of the invention, FIG. 4A is a partially cutaway perspective view of one type of direct reference path information sensing, FIG. 43 shows a partially cutaway perspective view of a further type of direct reference path information sensing, FIG. 5 shows a partially cut-away perspective view of a type of reference track arm sensing, fig. 6 shows a partially cut-away perspective view of one type of reference track arm sensor, fig. 7 shows a partially cut-away perspective view of a further type of reference path arm sensor, and fig. 8 shows a partially cut-away perspective view of yet another type of reference track arm sensor; fig. 9 shows a partially cutaway perspective view of the pin or needle portion of another type of reference path arm sensor, FIG. 10 shows a block diagram of a turntable vertical noise compensator system according to the invention, fig. 11 shows a cross-sectional side view of one type of vertical actuator that can be used in a plate plate VSK system, fig. 12 shows a cross-sectional side view of a further type of vertical actuator which can be used in a plate plate-VSK, fig.

13 shows a cross-sectional side view of yet another type of vertical actuator which can be used in a plate plate VSK system, fig. 14A shows a partially cut-away side view of a turntable using a vertical actuator, FIG. 14B shows an incomplete, partially cut-away side view of a further platen utilizing a vertical actuator, FIG. 15A shows a cross-sectional side view of a retrofit type vertical actuator for use with a conventional turntable, FIG. 15B shows a partially sectional side view of a. another type of retrofit vertical actuator for use with a conventional platen, FIG. 16A shows a block diagram of a prior art electric pickup arm damping arrangement, FIG. 16B shows a block diagram of a prior art pickup arm servo arrangement, and FIG. 17 shows a block diagram of a pickup arm-

VSK system according to the invention which uses direct reference path sensing; fig. 18 shows a block diagram of a further type of pickup arm VSK system according to the invention in which indirect reference path sensing is used, fig. 19 shows a block diagram of a further type of pickup arm VSK system according to the invention in which the error signal is included in a negative feedback loop, fig. 20 shows a functional block diagram of a pickup head VSK according to the invention, fig. 21A is a block diagram showing examples of combination interconnections between converters in a pickup head VSK according to the invention, fig. 21B is a block diagram showing an example of an alternative combination interconnection between converters in a pickup head VSK according to the invention, FIG. 22 shows a perspective view of a part of a pickup head VSK, fig. 23 shows a perspective view of a part of a further pickup head VSK, and fig. 24 is a block diagram of a for-for stronger VSK.

In all the embodiments to be described in the following, only the essential inventive features will be shown or described in detail. Except where otherwise stated, amplifiers, attenuators, rectifiers, differentiation circuits, integration circuits, feedback loop compensators, gain controllers and the like are thus used as is usually required in electronic technology. Except where it is mentioned otherwise, the detailed construction of cutting needles or pins, sensor transducers and actuator transducers, and the mechanical and electromechanical aspects of plates, pickup heads, pickup arms, drive motors and the like, will likewise not be dealt with.

In the various embodiments, b 1 e is the vertical position of an unmodulated portion of the plate (the reference path) sensed at or in the immediate vicinity of the signal pickup device, usually a needle or pin. An important element of the invention is the recognition that sensing in close proximity and with high resolution is effective in reducing mold grain noise. It goes without saying, however, that it is necessary for the reference track to be as spotless as possible. For example, it must be without scratches. Furthermore, the groove "horns" or ridges of material at the groove edges that project into the land area must preferably be removed during the plate manufacturing process.

Polishing the metal form is a known method of removing grooved horn. Another method is shown in fig. 2 which shows a further reference path-cutting needle 4 following the groove-cutting needle 6. The essentially flat bottom edge of the reference path needle not only removes the groove horns, but cuts away residual rumble modulations on the lacquer mother plate 2 and compensates for any vertical rumble introduced by recording - the lathe. Thereby, a completely silent reference surface is defined for use together with the reproduction designs according to the invention. In one embodiment (Fig. 6), a guide groove provides the reference path or track. In this case, the reference path cutting needle cuts an unmodulated groove close to the signal groove.

Sensing of reference trajectory information using direct means

Sensing of reference path information (ie, sensing the deformed or distorted undulating reference path) is a key element in the various embodiments. A generalized representation of reference path sensing is shown in fig. 3A and 3B. Fig. 3B will be described later under the heading "Sensing reference path information by indirect means". Referring to fig. 3A, the reference path information can be provided directly by a sensor that follows the signal pin laterally, but is vertically independent. The sensor 8 is attached to a reference plane. In a conventional turntable, as a typical example, the sensor will be attached to the pickup arm mounting surface. Theoretically, the attachment surface can be any suitable reference surface, including a stable surface apart from the turntable itself. A movable element 11, which forms part of the sensor 8, follows surface wave movements of the plate's surface. In practice, both plate-contacting and non-contacting sensors can be used, as described later in connection with fig. 4A and 4B.

In the version shown in fig. 4A, the sensing section of the arm may be vertically fixed and the transducer for sensing vertical displacement may comprise a non-mechanical device for sensing the plate surface 9, for example by means of an ultrasonic or capacitive device or by means of a light beam and detector (e.g. light-emitting diode and photodiode). A light beam which is preferably focused on the contact point of the pin, but with a s beam diameter which encloses at least one land area, can be angled at the surface. Vertical variations are then indicated as lateral variations which are sensed using one or more photodetectors. This technique has the advantage that it provides a relatively broadband error signal without any accompanying mechanical resonances. In this way, wind bias, rumble and mold grain noise can be compensated for at least up to several hundred Hz.

In the example of fig. 4A has the pickup arm 10, which is vertically fixed but can freely move laterally, a U-shaped end 12 in which a pickup head 14 is rotatable on a transverse pin 16. An arrangement of a light source 18 and detectors 20, 22, which resembles the arrangement of the sensor version according to fig. 5 which will be described later, generates the sensor signal.

In the simplest mechanical sensing designs, the reference path needle is placed on the pickup head in the manner shown in fig. 6 - 9 and which will be described later. In this case, the needle is relatively rigidly connected to the pickup head body and the pickup arm, which results in a relatively high vertical resonance frequency for the pickup arm. The needle can be used alone to reduce rumble and mold grain noise. It can also be used in conjunction with a pickup arm vertical position sensor to provide reference path information in a turntable VSK or a pickup arm VSK.

A further mechanical version for reference path sensing, which is shown in fig. 4B, uses a separate needle which is laterally connected to the signal pickup head, but is vertically independent of it. An arm 24, which can be pivoted for lateral (horizontal) movement only, has a first side support member 26 on which a pickup arm section 28 carrying the pickup head 14 is rotatably secured at 30. A second side support member and pivot which is enclosed in a housing 32 , has a shaft 34 which carries a secondary needle 36. A converter at the pivot in the housing 3 2 acts as a sensor for sensing the vertical movement of the secondary needle 36. The secondary needle is arranged to be lifted from the plate each time the signal needle is lifted. The needle 36 is preferably sized so that it touches the land area near the signal needle 38 of the pickup head 14.

Secondary needles or pins may be made of any of a variety of wear-resistant materials compatible with the plate surfaces and resistant to scoring effects, such as sapphire or diamond. Sensor transducers may be any of various types known in the art, including, but not limited to, electromagnetic or photoelectric transducers, Hall effect transducers, magneto-diode transducers, potentiometric transducers, or variable resistance, capacitance, or inductance transducers. The raw output signal from the transducer can represent position, velocity, acceleration or force (such as with a pressure-sensitive transducer).

The mechanical properties of the reference path sensor assembly can be optimized for the vertical sensing function only. The frequency for vertical resonance (sensor deflection and mass) should be placed significantly above the highest throw frequency, and in fact well into the audio frequency band, in order to stretch the highest correction frequency upwards, thereby reducing audible rumble and mold grain noise. The secondary needle must be placed very close to the primary needle, for example at a distance of no more than 1 mm for correction ti] approx. 50 Hz. An even shorter distance of approx. 0.1 mm for correction to approx. 500 Hz

is preferable for reducing shape grain noise in the middle area.

The secondary needle or sensing device may be positioned slightly ahead of the primary (signal) needle to generate a pre-fault signal. This is useful to relax the gain and phase conditions for electromechanical servo loops or to ensure optimal error cancellation where mechanical or electrical phase shifts are present, such as by low-pass filtering of the reference trajectory information.

Sensing of reference path arm information

Other embodiments of the invention use reference path arm information. This is the signal obtained by sensing the distance between the reference path or the reference track and the pickup arm (ie the pickup head). This signal will necessarily contain pickup arm movements and pickup arm/pickup head resonance effects. A first sensor version simply uses the vertical component information from the pickup head, as is known in the art. This method provides useful information about the frequency of arm/head resonance, but is limited to such cases and to the frequency range in which channel separation is deliberately reduced during disc recording (eg below 100 Hz).

In order to obtain reference track arm information up to higher frequencies, it is necessary to provide a land sensor which is independent of the signal needle. Non-mechanical sensing devices, such as those mentioned earlier in connection with fig. 4A, may be used, but attached to the pickup head holding arm or the pickup head instead of to a vertically fixed arm. An example of such a sensor is shown in fig. 5. A stereophonic pickup head 40 has a conventional cantilever shaft 42 and a needle or pin tip 44 shown in contact with a gramophone record 9. A light source 46, such as a light emitting diode (LED) or a diode laser, generates a beam of light to cause an area of the plate of the order of one millimeter in diameter or less is illuminated. The reflected light is received by one or more light receivers 48 and 50, such as photodiodes, in the same way as in connection with the description of fig. 4A. The lighting location and diameter are preferably chosen to illuminate the area in which the pin tip 44 is located and the adjacent land areas, so that the reflected light mainly reacts to local variations in the land at or just in front of the pin, which variations there are. representative of the rumble and shape-grain noise at this point. The output signal from the receivers 48 and 50 can be fed to a differential amplifier to provide an indication of local land variations. A suitable circuit arrangement can be made sensitive only to vertical land-position variations and not to the total light reflected, which will depend on groove modulations. Such methods are used, for example, in automatic light source focusing mechanisms.

Examples of mechanical versions of reference path arm sensors are shown in fig. 6-9. In each of these embodiments, a dual pin pickup head is provided in which a conventional pin tracks the groove information content and the secondary pin senses throw and rumble information. In the pickup head VSK design according to the invention, such a double contact combination has the possibility of improving both throw and rumble behavior in a uniform, complete pickup head. A third device for pickup head/plate surface contact can optionally be used, such as a brush or damper according to the previously known throw-tracking devices discussed above.

An ideal method for reference path sensing is shown in fig. 6 where a shallow, unmodulated guide groove 52 is arranged close to the main information-carrying groove 54 in a gramophone record 9a. The tip 56 of the secondary pin 58 in the pickup head 60 moves in the guide groove and senses both vertical and lateral throw and rumble frequencies. The embodiments according to the invention are then adapted to use both the vertical and horizontal information provided. Fortunately, sideways throw and. do not cause serious problems, and in a practical system it is sufficient to treat only vertical components.

Referring to fig. 7, the pickup head 62, in an arrangement suitable for conventional commercial gramophone records, has a main needle with a shaft 42 and a needle tip 44 which follows an information-carrying groove 54 in a gramophone record 9. The secondary shaft 64 and needle tip 66 are located on the one or both sides of the main needle and can enclose this in whole or in part. The contact area can be biased towards the outside of the plate if desired, so that pre-echo effects are minimized in the reference track information. The secondary needle tip has a mainly flat bottom with effective dimensions that are sufficiently large (e.g. a few fractions of a millimetre), so that it moves reliably on at least one land area and is thereby mainly insensitive to side information and to possible information content of the rill, as it only reacts to land-height variations which are a measure of wind bias and rumble. The tip 66 is guided laterally by the main needle, and can be held in place by a resilient coupling 68 which generally maintains the relative positions of the two needles, but does not interfere with the needle movements.

Another embodiment of the needles is shown in fig. 8. An oblong, block-shaped tip 70 for a secondary needle 72 spans the land between several grooves and is located in front of and on the outside of the main needle 42. As previously mentioned, the secondary needle tip can optionally be U-shaped (shown as an example as element 74 in Fig. 9) or O-shaped, in that it surrounds the main needle. In fig. 8, the contact area is shown biased in the direction towards the outside of the plate, in order to reduce pre-echo effects. A further practical matter is that the needle arrangement should preferably not capture dust, but should direct it away.

For most pickup arm and pickup head designs, the design of the reference track arm information sensors should be such that the tracking force for the main needle should preferably comprise the majority of the total pickup head tracking force to avoid affecting the lateral pressure forces on the pickup head and to avoid reducing the main needle force available for tracking of wind biases and large amplitude signals. A secondary needle tracking force which is a small fraction of the main needle's tracking force, for example 1/4, 1/10 or even less, is sufficient to sense the rumble components which have relatively small amplitude and low frequency. The secondary needle is preferably resiliently connected to the body of the pickup head, the resilience being preferably substantially greater than for the main needle. The preceding considerations with respect to compliance and tracking power apply primarily to counterweight pickup arm systems in which wind bias is not compensated. (In some systems, the secondary needle shaft can connect the needle relatively rigidly to the pickup head body). Furthermore, the effective mass of the secondary needle and associated moving parts, together with the bending or stiffness characteristics of the shank, should produce a high-frequency resonance well above the highest form-grain noise components of interest. Thus, a resonant frequency of at least 1-2 kHz would be suitable for the reference path sensor.

In a similar manner to the construction of conventional signal pickup heads, suitable mechanical damping can be applied to the secondary needle. A mechanical low-pass filter can be inserted if desired, so that the information provided by the secondary needle is band-limited to reduce sensitivity to dust and surface scratches.

Information from the reference path arm sensor is used in one way or another to cancel corresponding vertical information from the signal needle. Fully mechanical lifting arrangements can be used, as described below. In the simplest arrangement, with a non-yielding secondary needle shaft, the vertical movements of the pickup head body are subtracted from the corresponding movements of the primary needle. Alternatively, the secondary needle information can affect each other in the magnetic or electromechanical arrangements of the main signal converter in such a way that the error information is cancelled. In some arrangements, a separate or coordinated converter may be provided for the secondary needle. The combination of signals, as with interconnected coils, can be achieved in the pickup head itself, or the signals can be brought out for external combination. The signals can be used internally or they can also be brought out for use in other embodiments of the invention. For example, the high-frequency components from the reference path sensor can be used internally or brought out to the preamplifier for shape-grain noise reduction (pickup head-VSK or preamplifier-VSK), and the low-frequency components can be brought out to take care of windage via the influence of the turntable or pickup arm (platen-VSK or pickup arm -VSK).

Sensing reference track information using indirect means

As discussed above, accurate reference path information can be obtained directly, using a vertically fixed sensor. In an approximation, the vertical position of the pickup arm can be used, using the methods known in the art. A converter of the types mentioned above in connection with fig.

4B, is mounted between the pickup arm and the vertical pivot,

so that it provides an output signal that is proportional to the vertical position or angle of the arm and pickup head. This sensing method is effective for providing reference path information below the pickup arm/pickup head resonant frequency (eg 10 Hz). It is possible to use a relatively rigidly mounted secondary needle to raise the resonant frequency of the pickup arm. The reference path arm sensors described above in connection with fig. 5 - 9, are primarily effective above the resonance frequency. At or near the resonance frequency, phase and amplitude errors will be introduced into the reference path information by both of these methods.

These methods are therefore only effective at throw or rumble frequencies that are somewhat removed from the arm/head resonance frequency, i.e. normally below approx. 5 Hz and above approx. 20 Hz.

With an improved method, an essentially error-free throw and rumble sensing signal can be derived which enables the corrective action to be applied over the entire frequency range of interest (e.g. 0.5 Hz up to several hundred Hz) without interference due to arm/head resonance. The method uses a combination of the first and second sensing methods described in the previous sections (ie pickup arm sensing and reference path arm sensing) in a manner that is shown schematically in fig. 3B. This method is based on the recognition that both signals contain the same error signals (due to arm-head interactions), but in complementary form, so that they can be canceled to leave a difference signal that accurately indicates wind skew and rumble. . The vertical arm position signal x is an indication of the distance of the pickup arm 76 to the reference plane, while the reference track arm signal y is an indication of the distance of the pickup head 78 to the plate. The difference z is the pitch and rumble amplitude, i.e. z = x - y. The arm/head resonance error signals contained in the x and y signals from the pickup arm sensor 80 and the reference path arm sensor 82 cancel out in a combiner circuit 84 to provide a substantially error-free reference path information signal 86. The y signal can be derived using the various devices that have been discussed, using either the signal needle 78A, which in some cases provides useful information up to approx. 30 Hz, or the secondary needle 78B, with the help of which useful information is obtained up to several hundred Hz.

Plate plate - VSK

In fig. 10 is a block diagram of an embodiment of

a platter vertical noise compensator (VSK) according to the invention in which vertical position or displacement errors in the vicinity of the pickup transducer are sensed to control the vertical displacement of the platter in a closed loop servomechanism system. In effect, a reference plane for the disc is set by means of the bias-displacement level Yq applied to an adder/subtractor 90. The reference plane can optionally be made variable by means of a control 92. An error signal on a wire 94 is developed by subtracting the amplified reference path information signal on a line 96 from the bias signal. The error signal is supplied to an amplifier 98 and a vertical actuator 100 which controls the setting of the plate 9 in a direction mainly normal to the surface of the plate, at least in the area of the signal needle. A signal 102 relating to spurious vertical displacement of the plate in the vicinity of the pickup transducer is generated by a reference track sensor 104 and supplied to an amplifier 106.

For reduction of wind bias or throw, the feedback system should be effective at least in the frequency range from approx. 0.5 Hz to approx. 10 Hz. The system can be alternating current coupled, direct current coupled or a combination of these. To reduce rumble and shape grain noise, the bandwidth for the correction effect is stretched into the audible range (e.g. up to several hundred Hz). The correction can be completely mechanical, via the vertical actuator. Alternatively, the higher rumble frequencies (eg above 50 Hz) can be compensated via a pickup head VSK or a preamplifier VSK. If desired, a crossover network can be used to divide up the treated frequency ranges in an appropriate manner. The total system can thus make a significant contribution both to reducing wind bias and its side effects,

and to reduce audible noise.

The false vertical displacement processed by the system can optionally be displayed by means of an indicator device 108. A switch 110 can optionally be provided to break the loop to disengage the correction effect. Blocks 112 and 114 shall be described in connection with fig. 11.

Arrangements are needed to control the plate position in response to sensed variations in the vertical plate position in the vicinity of the pickup transducer. The plate height can be varied uniformly over its surface or only in the vicinity of the pickup converter. The necessary linear movements or angular movements can be achieved via the plate, the platen, the drive motor or the entire motor plate assembly.

A representative translational vertical actuator, which resembles a woofer with a flat speaker cone, is shown in Fig. 11. A metal plate 116 is supported by a drive shaft 118 in a bearing 120. The plate 116 is mainly arranged to provide rotat ion mass to reduce wow and flutter, and can be reduced in mass or even eliminated in some designs. The upper surface of the plate 116 is tapered to receive a light-weight record-supporting platter 122 which includes an index pin 124. The platter 122 may be partially hollowed out, with a cover portion 126, to minimize weight. The plate plate 122 is suspended in the plate 116 by means of one or more "arm crosses" or ring-shaped sets of corrugated material 128 and 130. The corrugated material can be a light fiber material of the type usually used in speaker suspensions. A lifting or thrust gear 132 which passes through the center of the drive shaft 118 and rests on a ball bearing 134, is driven by means of a turning coil 136 which forms part of a turning coil motor assembly 138 which is used here as a motion converter for the thrust rod 132. The assembly 138 comprises a permanent magnet 140 and a tubular core 142 which is supported by the magnet 140 to carry the coil winding 136 in proper relation to the magnet. Feed lines 144 and 146 are driven by amplifier 98 (Fig. 10). Springs or other such support device may be provided for balancing the weight of the platter assembly and for vertical centering of the motor assembly 138.

The disc plate 122 is preferably made of a material that is very light in weight, for example foam plastic, in order to minimize the mass that must be moved by the converter 138. The friction between the push rod and the drive shaft is also reduced as much as practically possible by using, for example, a nylon bearing or another low-friction bearing. Such bearings can be dispensed with in some constructions, especially if a further wheel cross is used at the bottom of the shock rod 132. Other types of mechanical coupling, such as hydraulic or pneumatic, can also be used.

The motor assembly 138 preferably provides a positive displacement output signal for a given electrical input signal. In this way, mechanical resonances in the system are avoided. This type of behavior can, for example, be provided by enclosing the motor unit itself in its own servo loop, preferably including a motor position sensor, such as 112 in fig. 10 (and fig.

11), and a suitable amplifier 114. Alternatively, if the motor unit simply provides essentially undamped power, it is necessary to provide a suitable degree of passive damping. However, this requires a large drive amplifier power. A more practical method is to ensure that the mass and elasticity of the plate-plate assembly results in a resonant frequency either well below or well above the frequency range of interest. The resonance frequency can be placed, for example, at approx. 50 Hz, to ensure a well-controlled behavior up to approx. 20 Hz. Passive mechanical damping using viscous materials can be used if desired. These considerations also apply to further designs of plate vertical noise compensators which will be described later. Such passive displacement control methods do not interfere with the operation of the record player when the vertical noise compensator is switched off. However, this is not the case with the designs of pickup arm vertical noise compensators to be described, in which electronic servos are preferred so that the pickup arm can be handled manually and can follow the groove in the normal way when the vertical noise compensator is disengaged.

In an alternative embodiment of the vertical actuator shown in fig. 12, the converter 138 is placed in a cylindrical cutout 148 in a modified plate 116a. The converter 138 thus rotates together with the plate 116a. The push rod is thus eliminated, along with its mass and friction. To drive the motor assembly 138, however, two slip rings 150 or another electrical transmission device are provided.

Alternatives to the vertical translation mechanisms that have been described concern control of only the plate height in the vicinity of the pickup transducer. With such a method, the turntable can be rocked or tilted in a controlled manner, so that vertical movement is provided along the line followed by the pickup head.

In the design example in fig. 13, a tiltable, plate-supporting platen 122a is spaced over a metal plate 116b. The plate 116b is provided only to provide rotational mass to reduce wow and flutter if necessary, and may be omitted in some designs. The platen 122a has a downwardly facing, conical, annular portion 152 which is coupled to the platen 116b for rotational movement, but which allows rocking or tilting of the platen. A drive shaft 118a for the plate 116b is supported in bearings 120a and is driven by means of a suitable rotary drive motor. A hollow center is provided in the drive shaft 118a for a push rod 132a which terminates in the disc plate 122a and an index pin 124. The push rod 132a is connected via a rotary joint 154 and a rod 156 to a turning coil motor assembly 138 which is of the type described above and is arranged to provide lateral movement to the bottom end of the rod 132a and thus to the rocker plate 122a.

Alternatively, the entire turntable and drive motor assembly can be tilted in relation to the pickup arm and the pickup head, in a similar way as for the design according to fig. 14A. A turntable 158, which is driven by a motor 160 via a drive shaft 162, is supported by a sub-plate 164 which, by means of compression springs 166, 168, is suspended from a base 170 to which the pickup arm and pickup head assembly 172 is mounted. A rotary coil converter assembly 138 controllably moves one end of the subplate 164 to tilt the turntable relative to the arm/head assembly.

In a variation of the arrangement in fig. 14A is a displacement transducer so arranged. that it causes vertical movement of the turntable and the drive shaft, possibly including the drive motor. For economic reasons, the displacement converter can be designed as part of the drive motor. Fig. 14B shows an arrangement where the entire drive motor and platter are moved vertically. A corrugated ring 130a similar to the material 130 holds the motor 160 suspended in an annular support 171 from the motor plate 164 to allow vertical movement.

Additional rocker designs that are useful as retro or retrofits to existing plate constructions are shown in Figs. 15A and 15B. A conventional turntable 164a driven by a shaft 162a has a tilting surface assembly 174 resting on its upper surface. The assembly 174 comprises a tilting disc plate part 176 which is essentially coincident with the size and shape of the underlying, existing disc plate 164a and has an extended circumference with downward-sweeping edges. The platen 176 has a downwardly tapered, annular portion which contacts a cone-shaped portion 177 which slides over the index pin 179 of the underlying platen 164a near the index pin and holds the existing portions of the platen 176 spaced above the underlying platen to permit tilting. To allow rotational coupling between the platters, a ring 178 of sufficient weight and surface friction to engage securely with the underlying platter surface is coupled to a hollow lower portion of platter 176 by means of a . device 180 which is rotationally rigid and yet flexible for tilting movement. Corrugated material as described above in connection with fig. 11 and 12, is suitable. The downward pulling edges 182 of the upper upper platen are metallic so that an electromagnet 184 arranged to pull in a controlled manner on the edge in one location controls the tilting of the platen.

In fig. 15B is an alternative rocking or tilting mechanism 183 in contact with the surface of a gramophone record 185, being placed in position after the record has been placed on the turntable. A linear motor 138 of a similar type as described in connection with fig. 13, provides the necessary rocking action via the rotation connection 154. . For simplicity when retrofitting such throw-compensating devices, the wind biases themselves can be sensed in an approximate way at the edge of the plate at a place located in the main shaft where the pickup head cuts the plate, using a lamp and photo-cell assembly 192. This sensing method is most accurate at the plate edges where the wind bias is greatest. Other sensing devices as described above can be used if greater accuracy is desired.

An advantage of a plate reproduction system using a plate plate-VSK, in particular of the vertical-translation type according to fig. 11, 12 and 14B, the possible use of a pickup arm which is essentially fixed vertically and mounted only for lateral movement relative to the plate. This simplifies reference path sensing which can be carried out directly as in fig. 4A and 4B. It also goes without saying that if a pivot is used either for

to accommodate any residual vertical movement of the record or to place the needle on the record, the pivot can be placed very close to the pickup head without danger of introducing wow due to windage bias. If desired, the vertical actuator can be controlled so that it causes the connection and disconnection of the plate and the pickup head. The vertical actuator can thus eliminate the need for an automatic lifting mechanism linked to the pickup arm.

The significant elimination of plate wind bias by means of plate VSK reproducers is led by a corresponding reduction of the many problems mentioned above in connection with wind bias. The effective existence of "throw-free" plates further enables the design of pickup arms, pickup transducers, and signal pins that take this operating condition into account. For example, it will be easier to optimize the construction of a counterweight pickup arm that must move mainly only in the lateral direction. The reduced tracking or grooving pressure and maximum deflection of the needles results in a different set of electromechanical parameters for pickup head design. The latter observation also applies to pickup arm VSK reproducers, which will be described below.

Pickup arm vertical noise compensator

Previously known feedback pickup arm systems are constructed in the manner shown in fig. 16A and 16B. The pickup arm vertical actuator is an electromechanical transducer designed to exert a force on the pickup arm or pickup head in a direction normal to the plate surface in response to an electrical signal from the sensor and amplifier. An additional motor unit can be used to operate in a similar manner on a horizontal basis (or 45°/ 45°).

In one previously known version which is shown in fig. 16A, a pickup arm sensor is adapted to monitor the vertical speed of the pickup arm. The negative feedback loop then acts to provide damping for the pickup arm. The attenuation depends on the loop gain, which must not be so high that it interferes with the tracking of passively tracked wind biases. The overall result is that pickup arm/pickup head resonance effects are reduced, but that the feedback loop is not included in tracking the record surface.

In other previously known versions, which are shown in fig. 16B, an attempt is made to use a servo loop to actively track the wind shear. The distance between the pickup arm and the plate's surface is sensed either by means of a separate converter or via the pickup head's output signal. This signal contains the arm/head resonance characteristics. The unseen and rapid changes of the loop's phase and gain in the area of resonance make compensation difficult, limit the loop gain that can be used and seriously disrupt the efficiency of the servo action. Thus, the previously known feedback pickup arm techniques are only partially effective in dealing with the problems of sheet wind bias.

Improved pickup arm systems in accordance with the invention are shown in fig. 17, 18 and 19. The designs according to fig. 17 and 18 utilize the improved direct and indirect fault sensing methods shown in FIG. 3A or 3B and which effectively eliminates the effects of mechanical arm/head resonance from the error signal. The embodiment according to fig. 19 uses a double closed loop in such a way that the sensed reference path arm information is brought to be essentially the same as the reference path information, thereby eliminating resonant effects. In some of the designs, both vertical and lateral operation (or 45°/45°) is possible, but for the sake of simplicity, the description shall be limited to vertical operation only.

The one in fig. The embodiment shown in 17 uses an open loop and direct sensing of the reference path information via a converter 8 which is independent of vertical movements of the pickup head. This type of sensor is shown in fig. 4A and 4B. The reference path information is amplified in an amplifier 196 and supplied to the pickup arm (pickup head) vertical actuator 89 which may be a rotary coil motor unit such as in the prior art feedback pickup arms. The signal polarity and gain are adjusted to provide a vertical drift of the pickup head body corresponding to the pitch and rumble wave motions of the record surface, a condition that would result in zero, or at least a minimal output signal from the signal pickup head. at least in the throw frequency range. Depending on the gain setting, the system can also undercorrect or overcorrect vertical errors.

When the gain is optimally set by the gain control 198, the system will be able to effect correction through and above the arm/head resonant frequency range only if the arm displacements are positively related to the reference trajectory information signal. This means that the arm must be damped, either mechanically or electrically, in order to eliminate the arm/head resonance and achieve a positive displacement effect. The actuator damping and/or servo considerations discussed above in connection with the turntable VSK designs are relevant here. An example of a servo loop 200 around the pickup arm vertical actuator is shown on the right side of FIG. 17 and comprises a pickup arm vertical movement sensor 80 (the converter is of the type described in connection with Fig. 4B, but however arranged to sense pickup arm vertical movement), an amplifier 202, an adder/subtractor 204 and an actuator drive amplifier 206 .The gain and other characteristics of the loop 200 are set to achieve good overall throw and rumble compensation behavior up to, for example, 200 Hz, with higher frequencies of the reference path information being sampled at 208 and utilized more conveniently in a preamplifier VSK to be described later . It should be noted that the actuator servo 200 is isolated and is used only to achieve a positive biasing effect in the present invention, so that much higher values of loop gain can be used than in the closed loop arrangements according to the known technique. The first mentioned embodiment according to the known technique uses the actuator loop only to dampen the pickup arm and not as part of an overall servo system. The other loops of the prior art include the arm/head transfer characteristic, which severely limits the usable gain before the oscillation. Switch 212 (Fig. 17) allows opening of loop 200 to disable the system for trial or demonstration purposes. The indicator device 108 allows observation of the reference path information.

The pickup arm VSK designs can be alternating current coupled, direct current coupled or a combination of these. A bias control (such as 210 in Fig. 17) can be used to adjust the needle force and/or raise and lower the needle. In a purely AC-coupled system, the tracking force can be determined mechanically as with the conventional pickup arms. However, a bias control can optionally be used to cancel the error signal for raising and lowering purposes.

Fig. 18 shows a further pickup arm VSK with an open loop in which a reference path information derivation system of the indirect type shown in fig. 3B. The gains for the amplifiers 214 and 214a are set to suit the conditions shown in FIG. 3B, whereby essentially pure reference path information is obtained that is unadulterated by arm/head resonance effects. The operation of the system is essentially the same as for the open loop system according to fig. 17. Under- or over-correction or optimal correction can be achieved, depending on the setting of the gain control. As in the system according to fig. 17, there are no particular limitations on the gain or other characteristics of the pickup arm-actuator-servo loop 200. Actuator damping is required only to

ensure effective roll and rumble compensation, not to prevent oscillations. The gain of the loop 200 is thus set to provide sufficient damping or a positive displacement effect of the vertical actuator, to provide good roll and rumble compensation in the frequency range of interest ( for example up to 20 Hz).

For economic reasons, the rocker arm sensors 80 and 80a can

be one and the same feeler. Likewise, the amplifiers 202 and 214 may be the same amplifier, with attenuation as necessary to provide appropriate levels (gains) at the inputs of the combining networks 216 and 204.

Fig. 19 shows a version of a pickup arm VSK according to the invention in which the throw and rumble error signal itself is enclosed in a negative feedback loop. The loop automatically provides pickup arm movements that correspond to the movements of the record's surface. As in the previous embodiments, it is essential that the correct error signal must be used, i.e. reference trajectory information without disturbance due to arm/head resonance effects.

In what follows, the operation of the system in fig.

19 if the outer loop 201 is broken at point A. The pickup arm will remain stationary throughout the relevant frequency range (0.5 Hz - 20 Hz) provided that sufficient gain is used in the vertical actuator servo loop (the inner loop 200). For example, the gains of the amplifiers 202 and 206 can be set to ensure this condition without the risk of oscillation, as there are no unusual oscillation-causing elements in the inner loop. Under this assumption, the output signal from the reference path arm sensor is pure reference path information. If the outer loop is then closed at point A, the pickup arm will follow the reference path, but with an amplitude that depends on the total gain for the outer loop. The gain of the amplifier 218 can be adjusted to provide the desired reduction factor in the output signal from the reference path arm sensor, which provides a reference path information, but with reduced amplitude. The invention thus removes the problems of the previously known pickup arm feedback systems (Fig. 16B) in that it effectively eliminates the cumbersome arm/head transfer characteristic from the feedback loop, so that the arm is affected by and follows the reference path.

Pickup head - VSK

Fig. 20 shows a functional block diagram of pickup head VSK embodiments of the invention. Wind bias (throw), rumble and shape grain noise from the main needle (groove arm sensor 220) is removed from the output signal in one way or another by means of an arrangement 222 which may be, for example, mechanical, magnetic or electrical in nature, utilizing the error information provided of the reference path arm sensor 224. This is preferably performed entirely within a unitary dual needle pickup head assembly. The operating parameters can thus be fixed and preset by the pickup head manufacturer, so that installation either on an original or replacement basis is a simple matter.

The reference path arm sensor 22 4 can be of the types discussed above and shown in fig. 5-9. Two independent sets of transducers 226 and 228 (eg, magnets and coils) may be provided in the pickup head, as schematically shown in FIG. 21A and 21B, showing examples of combination interconnections. The converter output signals can be further split to account for the left and right signals. An electrical or mechanical low-pass filter may be provided (eg 300 Hz cut-off frequency), with external control of the characteristics if desired, to reduce any non-rumble or non-form grain noise components sensed by the secondary needle, such as could be caused by scratches or rough groove edges. There may be arranged reference track information contact points as shown in fig. 20 and 21, whereby low frequency components can be utilized by turntable VSK or pickup arm VSK designs.

In a further version, which is shown as an example in fig. 22, the secondary needle shaft 72, instead of being coupled to its own transducer, is coupled to the stator components of the transducer so that rumble information sensed by the secondary needle 70 cancels rumble information sensed by the primary needle 44. This means that for rumble frequencies there is no relative movement between, for example, the piece of iron or the magnet 230 and the coils 232. Various other analogous canceling arrangements can also be used, using rotary coils, drive irons, drive magnets and the like. Two identical armature elements can share the same stator environment, such as e.g. two coils, each connected by its needle, sharing a common magnetic field.

The aforementioned stator components of the signal converter may comprise the pickup head body itself. For optimal noise cancellation, however, the mass to be displaced by the secondary needle should be as small as possible. The signal needle and the secondary needle thus preferably have independent, yielding connections 231 and 233 with the pickup head body. For optimal tracking, the secondary needle preferably provides the smallest proportion of the total pickup head tracking force and the smallest proportion of the total vertical stiffness.

Further, mechanically coupled arrangements are also possible in which the movements of the secondary needle cancel corresponding movements of the primary needle. An example is shown in the embodiment of fig. 23 where a U-shaped needle tip 74 partially surrounds the main needle tip 44. An A-shaped shaft 234 connects the tip 74 to first and second elements 274 and 276 which are fixed in relation to the pickup head. The main needle shaft 42 is attached to the crosspiece of the shaft 234 at a point 278. The distal end of the shaft 42 is connected to a conventional magnet or iron piece 242 which cooperates with coils 244. The secondary needle 74, which moves on more than one land area near the groove in which the main needle tip 44 engages reacts during operation to rumble frequency components and cancels movements of the magnet 24 2 as a result of corresponding reactions of the main needle.

Preamplifier - VSK

The reference track arm signal can be combined with the main needle signal in the electronic manner shown in fig. 24. This embodiment works in the main in the same way as the pickup head VSK described above, and is primarily applicable to sensors of the types shown in fig. 4A, 4B and 5, or on separate converter versions according to fig. 6-9. Each sensor has a respective preamplifier 244 and 246. A null control 250 is set for optimal noise cancellation in a combinational circuit 248. If desired, electrical filtering, signal delay corrections or other processing can be introduced into one or both signal chains to optimize the noise reduction effect under all operating conditions. For example, a transient noise suppressor 252 may be used to reduce the effect of "pops" and "clicks" caused by scratches on the disc and the like.

The signal on the disc being reproduced may be encoded in electronic noise reduction form, for example by using high frequency compression to reduce high frequency noise when it is played back, using high frequency expansion using the system known as "Dolby B". Such high-frequency noise reduction will be psychoacoustically very effective when combined with low-frequency plate noise reduction which is provided by means of the various embodiments according to the invention. The system of fig. 24 can provide for the playback of a "Dolby B" encoded disc by optional provision of a decoder 256 of the Dolby B type, preferably after the subtractor 248 or, although less desirable, in the signal chain for the blocks 220 and 244 before the subtractor 248.

Claims (1)

1. Gramophone record system comprising a cutting needle device (6) for embossing on a record a position-modulated signal groove in relation to a vertical reference position, and a device for reading the modulated groove in relation to the vertical reference, characterized in that the system further comprises a second cutting needle device (4) for embossing a defined land surface on the plate representing the vertical reference position, and a device (18, 20, 22; 32, 34, 36; 46, 48, 50; 56; 66; 70; 74; 78b ; 82; 104) for tracking the land surface to define the vertical reference relative to which the modulated groove is read. '2. Method of manufacturing a gramophone record, in which a signal groove is cut into the record by means of a first needle (6) whose vertical position is modulated so as to leave uncut lands between the orbits of the groove and groove horns projecting into the lands at both edges of the groove, characterized in that the groove horns and tops of the lands are removed by means of a vertically fixed, second needle (4) which follows the first needle (6) and impresses a vertical land surface on the plate.