US2182136A

US2182136A - Electrical sound recording

Info

Publication number: US2182136A
Application number: US192737A
Authority: US
Inventors: Ricchiardi Pier Carlo
Original assignee: Individual
Current assignee: Individual
Priority date: 1938-02-26
Filing date: 1938-02-26
Publication date: 1939-12-05
Anticipated expiration: 1956-12-05

Description

Patented Dec. 5, 1939 UNITED STATES PATENT OFFICE 8 Claims.

In the electrical recording of sounds, in particular with the present lmownelectro-mechanical sound record-cutting devices, when a record is made on a disc or on a film, linear and nonlinear distortions are observed which are due either to purely electrical factors, or to -mechanical factors.

For the former, record-cutting devices have been produced having an apparently constant impedance over the scale of recordable frequencies, but at the price of an extremely accurate manufacture. However, variations of temperature, of dampness, the ageing of certain parts cause the electrical characteristics of the recordcutter to vary in time, by causing the impedance constant to vary.

For distortions due to factors of a mechanical nature, in spite of the greatest care in manufacture, it has not yet been possible to produce perfectly linear record-cutting devices, since not only do all these apparatus show distortions due to mechanical defects, but furthermore in all these aparatus of the same kind, resonance effects are observed which are due to the masses in vibration and particularly such resonances vary with the nature of the support on which the recording is eifected, Thus, it is mechanically impossible to construct a recorder without a mechanical defect, without resonance, without variation with time and which is linear for any support on which it records.

The object of the present invention is not only to eliminate all these drawbacks, but also to enable linear recording to be effected on any support.

For this purpose, all the mechanical or electrical effects which are capable of causing distortion are corrected or compensated.

The invention is based on the principle that, in any recording, it is not the characteristics of the current which is supplied to the recording member such as a cutter, which matter, but those of the record such as the groove out.

My invention will be better understood from the following description taken inconjunction with the accompanying drawing, and its scope will be pointed out in the appended claims.

In said drawing:

Fig. l is a diagram of an example of an electrical sound recording cutter.

Fig. 2 is a diagram of a modified cutter.

Fig. 3 is a diagram explaining the correction of the distortions.

Fig. 4 is a diagram of a cutter recording system.

Fig. 5 illustrates the application of the invention to photo-electric sound recording.

In Fig. 1, l is the permanent magnet, and 2 and '3 the pole shoes; P is the armature carrying the recording needle and Z the coil receiving the 5 modulated current, So far everything is pro-- vided as in the most classical cutter. But the armature P has an extension PX placed in a coil N which is in its turn placed in the magnetic field produced by the

pole shoes

4 and 5. Any 10 vibration of the armature P, with its extension PX produces a current in the coil N, exactly as 0 occurs in a reproducing pick-up. At the ends of the coil N, there will therefore be a current which is proportional to the movements of the armature. 15 P. If no distortion is introduced when recording, the current sent into the coil Z has exactly the same aspect as that issuing from the coil N.

In any case, the output current from the coil N has no connection with the output current of the amplifier, but corresponds exactly to the aspect of the recorded groove. If, instead of a perfect sinusoid, such as that sent into the coil Z, two truncated sine waves are recorded for any reason, the output from the coil N is not a sine wave, but two trimcated sine waves,'since' the output current from the coil N reflects the aspect of the groove traced by the recording needle P.

The case of a recording with linear distortion will now be considered. In Fig. 4, a, transformer l, 2 Supplies an amplifier 3. It is assumed that the power input to the amplifier 3 is absolutely constant and has a frequency which varies progressively over the scale to be recorded which is shown by the power curve A (Fig. 3). At the 35 output end of the amplifier 3 there is therefore a response similar to that of the curve A and this current is applied to the recording member 4 which it actuates. The two ends of secondary 2 of the input transformer I are also connected to the input of the amplifier 5 and transmit thereto a current which is equal to the input current of the amplifier 3. As the two

amplifiers

3 and 5 have the same characteristics, there is 45 at the output 6 a current which is absolutely equal to the output current of the amplifier 3, since said two amplifiers which have the same input source, operate in parallel. In other words, the response curve of the two amplifiers is the same (curve A of Fig. 3).

It is now assumed that there is a linear distortion in the recording. There is therefore an amplitude distortion in the recording member, either owing to an electrical phenomenon (resotortion introduced by the recording. For a con,-

, stantinput power, a similar curve to the curveA (Fig. 3) is therefore obtained at the of the amplifier 5 Fi 4), and a curve to the curve B (Fig. 3) is found to have been recorded by the amplifier 3 (Fig. 4)

It is therefore obvious that the introduced by the recording is equal to the difierence between the original curve A and the recording curve B. But the current induced in the coil N, as explained above, has the same aspect as that shown by the curve B. Said current, which is called auxiliary current, is then suitably amplified or reduced by I (Fig. 4) The output of I is connected to the of a transformer having two primaries 6 and 8.

The flux of said two primaries is elongated so as to induce in the secondary a current which. is the result of the diiference of the currents which flow through the two primaries 6 and 8.

At the end of the secondary 9 there will therefore be a current resulting from the diflerence between the curve A and the curve B. Said current corresponds to the amount of distortion introduced during the recording by the recormg member 4 and its electric Said current,

called pilot current, is conveyed to power am- In order to give a better lmdg of this compensating current, reference will be had to the curves of Figure 3. 7

When the current produced or by the recording member, after cation or reduction, is at the same level as the current of the amplifier 5,the curve B has the same level as and is identical with the curve A, and as the two fluxes of the two primaries are in opposition, the output current from thesecondary9 (Fig.3) lhitwhenflaecnrveB has a lower level than the curve A, there is in the secondary 9 a current in a which will be called .positive, whereas when the curve B is at a higher level than the-curveAJhereis a current of opposite or negative sign in the s'econdary 9.

.'1'hus,assumingthatatthepointlofthe curvesBandA,thecurveBisatalevel-15db relatively to the curve A which is at 0 decibels, the current fi'omthesecondary .9 is amplified or reduced by the II and controls the amplification factor of the amplifier 3, increasing same by 15 db.

Owingto this fact, the currentattheoutmltof 'the amplifier3givesanincreaseofpowertothe recorder I, by'the amount 11 for the wtrent produced in the coil N and amplified by I:

to be increased by 15 db., so that the cnrrmt flowingtliroughtheprimarydthesame I levelas that flowing through the. i. 7

As soon as this level is reached, time n no longer any current in the secondary S and, owing,

to this fact, the amplifier 3 again under.

normal conditions, since at this instant, the curve B coincides with the curve awnemw any distortion will 75 Atthepoint 2,ifowingtoanyeitectofmonaneeorforanyotherreasomtheamplifierl gives a-level which is higher than that of the original curve A, for'example, by 15 db, a cur-5 I rentisinducedinthecoilNwhichgivesinthe primarydacurrentoiwhichthestrengthis greater by 15 db. than that flowing through the primary 5.

. Owing to this fact, the current induced in 5 has a negative direction and reduces the ampliflcation factor of the amplifier 3 to the extent necessary for the recording effected by 4 to give aninduced current in the coil N of which the level is lower by 15 db. than that induced therein before correction, that is to say which brings back thecurveBtothesamelevel asthe curve A. And this result is obtained without any inertia or dephasing, since the compensating action is instantaneous and the correction is efl'ected as soon as the distortion arises.

The same system naturally corrects any nonlinear distortion, conditionally of course on dephasing being avoided between the input current of the secondary 2 and that of the secondary 9. But there is no difliculty in obtaining this result, particularly if instead of using transformers'to place the current directly at the output of the amplifier in opposition to the current produced by the vibrations of the, armature carrying the recording needle, solely tubes are used. a

The detailed description is given solely by way of example, since it is obvious that the principle of the invention can be applied in various manner without exceeding the scope of the invention- Thus, instead of a coil such as N shownin Fig. 1, in order to avoid any direct induction, the extension of the armature may operate as the slider of a rheostat R according to the modification illustrated in Fig. 2. Or again, it may, compress a piezo-electric crystal so as to ob-- tain therefrom the necessary voltages at the output; or again, this same armature may, with or of which the capacity varies proportionally to the position of the armature. 'Ihus, the means for placing the current directly at the output of the amplifier in opposition with the current produced by the vibrations 6f the armature, may

be quite different from those illustrated as an example, without exceeding the scope of the invention. Thus this opposition of the two currents, instead of being eflfected by a transformer,

.maybeeflectedbyahibesystem,oragainby any other system notshown, without for this reasondeparting from the principle 01' the invention.

Said invention, which 'is described in detail for a sound cutting device, is consequently advanapplicable to any system for recording on a disc or on a flhn, either by cutting, or by optical means, since it suilices forthe recording member to be in operation in order to detect therein a form of distortion which is compensated by the system illustrated. Thus,

films, illustrated in m. s, the light from the lamp A is condensed by the optical system and'c impinges, in the shape of a beam of light, on the recording galvanometer G. From the mirror of the latter a part of said beam passes through the optical system SP and impinges on the film F where it efiects the recording. Another part of the luminous beam which is reflected after modulation from the mirror of the galvanometer G, impinges on the prism L and is reflected on to the mirrors M and N whence it is reflected on to the photo-electric cell R. It is obvious that the output current from the photo-electric cell R has absolutely the same aspect as the sound recorded on the film F. The output current from, the photo'- electric cell R, in this type of recording, therefore, replaces the current illustrated as the output current of the coil N of Fig. 1 or of the rheostat 2 of Fig. 2. Thus the analogy between the two systems of recording is obvious, as'are likewise obvious the advantages procured by this novel system, for compensating any distortion,

in any recording 'system wherein the recording member is subjected to any movement.

The present invention therefore applies, not only to recording devices operating by cutting on discs or on films, but also to all recording de-. vices, either electro-mechanical, or electro-optlcal wherein the recording member or element is subjected to an oscillatory or vibratory movement.

I claim:

1. In the electrical recording of sounds, the 7 method which consists in causing the recording member itself to modulate an auxiliary electric current which is proportional to the sound recorded with its distortions, placing said auxiliary current in opposition with a current issuing directly from an amplifier connected in parallel with the amplifier piloting the recording mem-- ber, utilizing the result thus obtained from the two currents for piloting the amplification factor a of the amplifier jwhich actuates the recording member in order to correct all distortions introduced by the recording. member or by the electricalcircuit of same. k

2. In the electrical recording of sounds, asystem comprising a source of supply, an input amplifieractuating a recording member, means for producing an auxiliary ing said auxiliary current in opposition in a receiver with a current supplied direct by said source of supply through the intermediary of amplifying and transforming means, and means for conditioning the resulting output current that which'would havebeen produced by the ,recording member proper.

4. A system according to claim 2, wherein the auxiliary current is produced by an intermediate,

member giving a current which is proportional to that which would have been produced by the recording member proper.

tem comprising a source of light, conditioning current which is the image of the recording effected, means for plac- 1 circuitof same; 5. In the electricalrecording of sormds, a sys-' means, a recording member adapted to modulate the light, means whereby part of the modulated light is caused to act on a film, and means causing another part of the modulated light to act on a photo-electric cell which produces-an auxiliary current which is the'ima'ge of the recordber, placing said current'in "opposition with a current obtained directly across the terminals {of the source actuating the recording member, utilizing the difference thus obtained from the two said currents as a pilot current for piloting said auxiliary current and the current directly emanating from the actuating source, andtherebycorrecting for'all the distortions introduced by the recording member or by the electrical circuit of same.

7. In the electrical recording of sounds, the m'ethod'which consists in causing the recording member itself to produce an auxiliary electric current which is the exact image, of the sound the amplification factor of the amplifier. which actuates the recording member propor-' 'tionally to the algebraical difierence between as recorded with all its distortions by said member, placing said current in. opposition with a current derived from the source before the amplifie utilizing the difference thus obtained from the two said currents as a pilot current for piloting theamplification factorof the amplifier which 'actuates the recording member proportionally to the algebraical diflerence between said auxiliary current and the-current directly emanating from the actuating source, and thereby correctingfor all the distortions introduced by the recording member or by the electrical circuit of same.

8. In the electrical-recording'of sounds, the method which consists in causing the recording member itself to produce an auxiliary electric current whichis the exact image of the *sound as recorded with all its distortions by said memcurrent derived amplifier stage in which the correction is effected, utilizing the difference thus obtained from the two said currents as a pilot current for .piloting the amplification factor of the amplifier which actuates the recording member propertionally to the algebraical difference between by the recording member or rum nant-o nrccmsapr.

ber, placing said. current in opposition with a from the ,amplifier before the said auxiliary current and the current-- directly emanating from the actuating source, and thereby correcting for all the distortions introduced, by the electrical