Patent GB-1182810-A (GB)
Title: Medium for the Recording of at least Two Signals in Multiple-Groove Recording and Method of Producing it.
IPC: G11B3/72
Filed: 1967-11-21
Abstract: 1,182,810. Magnetic and mechanical recording. TELDEC TELEFUNKEN-DECCA SCHALLPLATTEN G.m.b.H. 21 Nov., 1967 [21 Nov., 1966], No. 52831/67. Heading G5R. A recording medium has at least two signals recorded in a common groove; the medium is magnetizable to a depth at least sufficient to include the groove; the recording is a combination of a magnetic recording produced by mechanical deformation at relatively high frequency of a portion of the groove surface for a first signal, and a conventional mechanical recording at relatively low frequency consisting of mechanical deviations of the surface of the groove, or deviations of the groove as a whole, for a second signal. The medium 1, Fig. 1, may be in the form of a disc, tape or cylinder, and may be magnetizable throughout its depth or be magnetizable to a depth sufficient to include the groove 2. The high frequency magnetic recording 3 is illustrated by high frequency mechanical waves along both sides of the groove 2; these have been produced by a stylus operating in a hill- and-dale mode and fed with, e.g. the picture signal of a composite television signal. The low frequency mechanical recording is illustrated by low frequency undulations of the sides of the groove 2, reference numeral 3a indicating both a maximum and a minimum of such undulations. Preferably these are produced by the same stylus as is used for the first signal, simultaneously. The second signal may correspond to monophonic sound, and may be recorded in the hill-and-dale mode t, Fig. 2, or in the lateral mode s. Alternatively the second signal may correspond to stereophonic sound, and be recorded in tracks at + 45 degrees and - 45 degrees to the normal to the record surface, (see Fig. 2). Preferably the stylus has a triangular profile. Preferably each signal is recorded in the form of a modulated carrier wave, the frequency range of the first signal being chosen so that it does not extend into that of the second signal. Difficulties in the recording, of the higher frequency first signal especially, are avoided by recording at a considerably reduced speed in relation to the normal passage of the signals, the deflection frequencies of the stylus being correspondingly reduced. Playback.-A single playback needle preferably is used, consisting of a portion 4, acting purely mechanically, and a portion 5 acting mechanically and magnetically. The needle has a spherical tip whose radius must conform to certain limits of size; thus, the radius must be so large in comparison with the longest video wavelength (e.g. 10 times that wavelength) that the needle tip cannot drop into the " dales " between the " hills " of the magnetic recording, and must be so small in relation to the shortest audio wavelength that it can follow the undulations 3a. For the magnetic playback, either an external field, NS, Fig. 1, must be provided, or the medium 1 must be magnetically hard and magnetized. Track 3 with part 5 of the needle produces a gap fluctuating in width during playback, and the resulting flux variations are " read " by coil 7, Fig. 2. The needle is also connected in a conventional electromechanical transducer for " reading " track 3a.