US2029389A - Recording and reproduction of electrical impulses - Google Patents

Recording and reproduction of electrical impulses Download PDF

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Publication number
US2029389A
US2029389A US654667A US65466733A US2029389A US 2029389 A US2029389 A US 2029389A US 654667 A US654667 A US 654667A US 65466733 A US65466733 A US 65466733A US 2029389 A US2029389 A US 2029389A
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United States
Prior art keywords
impulses
reproduced
volume
current
recording
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Expired - Lifetime
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US654667A
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English (en)
Inventor
Ringel Abraham
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RCA Corp
Original Assignee
RCA Corp
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Filing date
Publication date
Application filed by RCA Corp filed Critical RCA Corp
Priority to US654667A priority Critical patent/US2029389A/en
Priority to GB3366/34A priority patent/GB425256A/en
Priority to DER89802D priority patent/DE651133C/de
Application granted granted Critical
Publication of US2029389A publication Critical patent/US2029389A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B3/00—Recording by mechanical cutting, deforming or pressing, e.g. of grooves or pits; Reproducing by mechanical sensing; Record carriers therefor
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G7/00—Volume compression or expansion in amplifiers

Definitions

  • This invention relates to the recording and reproduction of electrical impulses such as those found within the audio frequencyrange, and has for its principal object the provision of an improved apparatus and method of operation where'- by ground or background noise is eliminated, the
  • volume range in sound recording and broadcasting is increased, and overshooting due to overy modulation of the sound during recording is prevented.
  • tone color and"tone volume In the reproduction of sound, and particularly of music, two essential factors must be considered, namely, quality and quantity. In music these factors are referredto as tone color and"tone volume; in engineering they are associated with frequency response and amplitude, respectively.
  • tone color and"tone volume In engineering they are associated with frequency response and amplitude, respectively.
  • the lower limit of volume is governed by the soycalled noise level, while the upper limit is governed by the overload point of the equipment. In recording, this point is reached when one groove is over-cut' into the adjacent groove.
  • the permissible volume range in either broadcasting or disc recording is of the order of or 30 decibels (approximately to 1 in amplitude). From the standpoint of the musician, it would be highly desirable to have this range increased to 60 or rI0 db., to reproduce, for instance, the music of a symphony orchestra.
  • volume-controlling signal referred to hereafter as the control-tone.
  • the volume range in phono- 4" graph reproduction can be extended to at least Briefly, the broadening of the reproducible dynamic or volume range is accomplished in the following manner. Suppose that a passage is bethan the ground noise of the system. Heretofore, the gain of 'the recording amplifier was raised at this point to raise the level of the music to a value above that of the noise.
  • the recordist increases the gain in the same manner, but he also adds an additional sub-audible tone, having a diierent frequency such as 20 cycles, to the cutters input.
  • an additional sub-audible tone having a diierent frequency such as 20 cycles.
  • the voltage 60 obtained from this additional control tone is used
  • musicians have many' ing recorded, Whose minimum amplitude is lowerl to reduce the gain of the reproducing amplifier.
  • the reproduced signal may be reduced very nearly to the original level, and at the same time the favorable signal to noise ratio, ob-
  • amplitude is, of course, determined by the reproducing equipment and may be made as high as desired so that the reproduced dynamic range may be made almost identical with the original.
  • volume control current which has a frequency outside the frequency range of the desired signals, is recorded simultaneously with the signals on the same rec- 15 ord area, and has its level controlled either manually or automatically to maintain the desired signal at a continuously high level or within a com ⁇ paratively narrow range of levels.
  • the 20 control current may, for example, have a subaudible frequency and may have its level controlled to increase the volume of the audio impulses at low modulation and to decrease the volume of theseimpulses at high modulation, thus 25 maintaining the signal current within a comparatively narrow range of levels.
  • control current is separated from the signal current either electrically or electromechanically and is rectified and is utilized to re- 30 store the volume of the reproduced sound to its original value. It will be readily understood that such a control current may also be utilized in connection with radio broadcasting to correct inaccuracies due to defective rendition in the studio' 35 and the like.
  • Further objects of the invention are to increase the dynamic range of disc reproduction from approximately 25 db., as at present, to 50 db., to increase the signal to noise ratio in reproduction 40 to a more favorable value by permittingthe recording to be done at a high and more or less uniform level, and reducing this level to the original by means of the control tone, and to extend the volume range of sound lm reproduction or radio 4' broadcast transmission.
  • Fig. l is a diagrammatic representation of a recording system involving the invention
  • Fig. 2 is a diagrammatic representation of a reproducing system constructed in accordance with the invention
  • Fig. 3 is a modified form of recording apparatus arranged for automatic volume control of the recorded sound
  • Figs. 4, 5 and 6 are explanatory diagrams il- 60Y -cordance with the invention',
  • Fig. 7 is a side view of an electrical reproducer which is operable electromechanically to separate the control and signal impulses-reproduced from a grooved disk or the like, A
  • Fig. 8 is a plan View of the part of "the reproducer which functions to repro uce thecontrol impulses recorded on a. grooved disk, and
  • Fig. 9 is an explanatory diagram relating to the operation of the composite reproducer of Figs. 7 and 8.
  • the recording system of Fig. 1 includes a microphone or pick-up device I0 from which electrical impulses are supplied to a recorder I I through 4a suitable channel including anamplifler I2, an
  • the channel ⁇ 2I3I4 may include additional elements such as a mixer and other usual elements utilized in a channel of this character, and that the recorder II may be terial.
  • Control current produced by a generator I5 . is injected into the channel I4 through means including a potentiometer I6 which may be mechanically coupled to the potentiometer t3, a coupling tube Il, a transformer I 8 and a low pass filter I9. 't l Under these conditions-the signal and control currents are simultaneously recorded on the same recording area lor sound track. The levels or volumes of the control and signal currents may be varied simultaneously in the case of integral control of the potentiometers I3 and I6.
  • the frequency of the control current may lie within the subaudible range, a frequency of the order If the original sound is too loud to be recorded or modulated, its volume is reduced and the volume .1 or amplitude of the control current is decreased corder, and increasing the volume of signal which l may be recorded.
  • the soundy track area should be allowed for the sound record and that the remainder utilized to record the control current i. e. a maximum of about 90% of the sound track should be utilized for the loudest sound or the highest percentage modulation.
  • the lowest recording level of the signal should not be less than 25 to 30 per cent of full scale. If the signal level-decreases below this range of values, the potentiometers I3 and I6 are operated to raise the levels of the signal and control currents to the proper Value.
  • the gain is increased by the potentiometers I3 and I6 to a point where the control current is recorded at maximum level so that the high amplitude of the control current will reduce the amplification of the system and thereby lower the ground noise levels in the silent passages during reproduction.
  • the level of the recorded control current is high, the
  • volume of the reproduced sound is low.
  • volume of the reproduced sound is high.
  • the reproducing system of Fig. 2 includes a record 2li/and' a pick-up device 2
  • a resistor 28 is connected in the common lead of the input circuits of the tubes 24-25. Volume control current is supplied to this resistor from the pick-up device 2
  • the function of separating the signal and control current impulses may, in the case of reproduction from a disk record, be performed by a composite pick-up device instead of the electrical filter 29.
  • variable fr tubes 24 and 25 may be of the type commonly having the designation UX235 or RCA-58.
  • the power amplier 2l may be omitted if these tubes are designed to have sufficient output current, to operate the loud speaker 28.
  • the volume control of the recording system of Fig. 1 is effected by manual manipulation of the potentiometers I3 and I6, automatic means may be provided for producing this result.
  • electrical impulses are supplied from' the pick-up device or microphone I0 to the recorder I I through a channel including the amplier I2, a transformer 35, a push-pull amplification stage 36-31 containing variable p. tubes, a transformer38, a high pass illter 39-40-4I, and the power amplifier I4.
  • Volume control current is supplied from the generator I5 to the recorder II through a channel including ai transformer 42, a push-pull ampliilcation stage 43.-44 using variable a tubes, a transformer 45, a low pass' filter 46-41-48 and the power amplier I4.
  • the sound record appears somewhat as indicated in Fig. 4, the control current being indicated as a sine curve 62 on which are superimposed the signal waves 63.
  • the control current being indicated as a sine curve 62 on which are superimposed the signal waves 63.
  • the audio waves are likewisesuperimposed on a groove of sinusoidal form.
  • the signal current is roughly indicated by the curve A, the control current by the curve B, and the resultant current by the curve C.
  • the electrical reproducer illustrated by Figs. 7 and 8 includes an electrical reproducer 10 provided with a support or tone arm 1l pivoted at 12. This reproducer 1
  • a reproducer l5 which functions to reproduce the control current impulse recorded on the record 13.
  • This control current reproducer includes a magnet 16 which is provided with an armature 11 mounted on a .resilient support 18 and having an adjustable weight or inertia means 19 for tuning the reproducer to the control frequency.
  • a pick-up coil 80 Mounted on the armature 11 near the pole pieces of the magnet 1E is a pick-up coil 80 wherein the control current is generated.
  • the method of sound recording and reproducing whichv includes superimposing on the audio impulses a control current of inaudible frequency, raising the level oi said control current when the volume of said impulses is relatively low and lowering said level when said volume is relatively high, reproducing said current and impulses, ⁇ *and controlling the volume of said reproduced impulses in accordance with said reproduced current.
  • the method of sound recording and reproducing whichl includes superimposing on the audio impulses a control current of inaudible frequency, raising the level of said control current when the volume of said impulses falls below thirty per cent of its full scale value and lowering said level when said volume exceeds ninety per cent of its full 'scale value, reproducing said current and impulses, and controlling the volume of said reproduced impulses by means of said reproduced current.
  • the method of sound recording and reproduction which includes superimposing on the audio impulses a control current of inaudible frequency, raising the level of said control current when the range of said volume is relatively low and lowering said level when said range is relatively high, reproducing said impulses and current, and controlling the volume of said reproduced impulses by means of said reproduced current.
  • the method which includes producing audio impulses, superimposing a current of inaudible frequency on said impulses, reproducing said impulses and current, and controlling the volume of said reproduced impulses by means of said reproduced current.
  • means for producing audio impulses means for producing an inaudible impulse
  • means responsive to said audio impulses for controlling the levels of said audible and inaudible impulses
  • means for causing said audible and inaudible impulses to bie/recorded in superimposed relation with respect to one another means for reproducing said audio and inaubile impulses, and -means for causing the volume of said reproduced audio impulses to be controlled by said reproduced impulse of inaudible frequency.
  • the method of sound recording and reproducing ⁇ which includes superimposing on the audio impulses a control current of inaudible frequency, raising' the level of said control current when thevolume of said impulses falls below thirty percent of its full scale value, yreproducing said current and impulses, and controlling the volume of said reproduced impulses by means of said reproduced current.
  • the method of sound recording and lreproduction which includes superimposing on the audio impulses a control current of inaudible frequency, rais ng the level of said control current when the range of said volume is relatively low, reproducing said impulses and current, and controlling the volume of said reproduced impulses by means of said reproduced current.
  • the method of sound recording and reproducing which includes superimposing on the audio impulses to be recorded a control current of inaudible frequency, raising the levels of said impulses and current during the lwer volume ranges of said sound, reproducingv said impulses and current, and restoring the level of said reproduced impulses to its original value' by means of said reproduced current.
  • Apparatus comprising a pickup device

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  • Signal Processing Not Specific To The Method Of Recording And Reproducing (AREA)
US654667A 1933-02-01 1933-02-01 Recording and reproduction of electrical impulses Expired - Lifetime US2029389A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
US654667A US2029389A (en) 1933-02-01 1933-02-01 Recording and reproduction of electrical impulses
GB3366/34A GB425256A (en) 1933-02-01 1934-02-01 Recording and reproduction of electrical impulses
DER89802D DE651133C (de) 1933-02-01 1934-02-02 Tonaufzeichnungs- und Wiedergabeverfahren

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US654667A US2029389A (en) 1933-02-01 1933-02-01 Recording and reproduction of electrical impulses

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US2029389A true US2029389A (en) 1936-02-04

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US (1) US2029389A (de)
DE (1) DE651133C (de)
GB (1) GB425256A (de)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2530579A (en) * 1946-10-15 1950-11-21 Rca Corp Speech inverter
US2689884A (en) * 1953-03-27 1954-09-21 Samuel J Raff Recording stabilizer

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2530579A (en) * 1946-10-15 1950-11-21 Rca Corp Speech inverter
US2689884A (en) * 1953-03-27 1954-09-21 Samuel J Raff Recording stabilizer

Also Published As

Publication number Publication date
GB425256A (en) 1935-03-11
DE651133C (de) 1937-10-08

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