’ Aug. 26, 1941. H. FLETCHER - 2,254,034 SOUND RERECORDING SYSTEM Filed April 5, 1940 , /3 AMI/.9 / 2 4 \mI AMP 9/ \. 5 ,2 / 6 .9 AMP I a i WW’ ,w’ 7 IN l/EN TOR By H. FLETCHER ' - @Mw A TTORNEV remnants-reign j v. 192154934; ~ . umrso7~sTATEs "PATENT - orrlcs ' ‘ assure _ , _' ' SOUND BEBEOOBDING SYSTEM. vHarvey Fletcher, Flushing, N. Y., assignor to Dell 1 . Telephone Laboratories, Incorporated, New York, N. 1., a corporation of New York . Appummn April 5, 1940, Serial No. 32am 1 ._ ' ‘ s cum. (t1. ?ll-100.1) This invention relates, to sound rerecording‘ systems and particularly to systems for rerecord ing volume compressed records. ' . ' pansion of the volume range, and also to control the arbitrary volume level about which this ex ‘ pension takes place. . The amount of arbitrary enhancement of the . Bound recording systems are known in ‘which the volume range of the original sound is re duced or compressed and a separate record is made of the degree of compression. This sep arate record of the degree of compression, which volume range afforded by manipulation of ‘the _ attenuator I is limited by the characteristics ~01 - the compressor used in the channel which pro duced the original record I, and the character istics of theexp'ander which will be used in the may conveniently be called a control record, may ; channel used for the reproduction of the rere-, ‘be recorded as a slowly varying direct current, as 10 corded record 5, this expander preferably having shown in United States Patent 1.623.756. April the same characteristics as the expander l0. As I 5, 1927, C. F.’ Sacia, or as a modulated carrier current as shown ingUnited States Patent 2,069», 810, February 9, 193?. H. D. Arnold. - _ .a control current is used for the control of the compressors, andexpanders. the degree of com- '. ' The object of‘ the present invention is, during 15 pression in the compressed range may be sub stantially complete, as shown in United States rerecording,.to arbitrarily vary the volume level Patent 1,623,756 to Sacia. ‘The compression and of the rerecorded currents so as to enhance the ' expansion need not be used throughout the whole volume contrast in the reproduced music. -' range of volume recorded, that is, the lower A feature of the invention is,lduring rerecord volume levels may be rerecorded and reproduced I‘" ing to arbitrarily vary vthe rerecorded control 20 without compression and expansion, only the ' ‘current, in such manner as will result in a‘ de higher levels of volume being compressed in order sired'variation of the volume of the reproduced " to prevent overloading of the_ recording. device. sound without impairing the function of the However, no matter what type of compression control current to restore the original volume I '25 and expansion is used, the expander l0, and the variation in the sounds diagrammatic form a ' expander used in the reproducing channel, must The drawing shows in have a range of expansion larger than the range rerecording ‘system including one embodiment used in compression, that is, the range used in of the invention. compression‘ plus the variation imposed on the ' The compressed sound is reproduced from the record I by the pick-up device I and, after suit 30 control current by .the attenuator 8,‘ mustnot exceed the available range of expansion in the 'able ampli?cation, in the ampli?er 3, is rere corded by the recorder l on the recording ‘medium I. If desired, adjustable frequency dis criminative networks may be associated with the ampli?er 3 in ‘the usual manner to modify the frequency pattern of the rerecorded sound. The pick-up device 2 is of any suitable design adapted for reproducing the record on the record ma terial I. ' ‘ The control record, on the record material expander ill, or in the expander in the reproduc ing channel. In a typical embodiment of the invention, compression is applied to the 'upper thirty decibels of the volume range and com presses this range into a range of some ten deci bels on the original record. The compressor in the recording channel thus operates over a range of thirty decibels. The expander Ill, and the I, v4.0 expander in the reproducing channel operate . is reproduced by the pick-up device 8 and, if desired, ampli?ed in the ampli?er '|. After ampli?cation, the control currents are, supplied through the variable attenuator 8 to the recorder over an expanded range of ?fty decibels. Thus the manipulation of the attentuator 8 can shift‘ the operating range of the expander l0, ten deci bels above or below normal without interfering v I and are recorded on the recording material 5. 45 in any way with the automatic expansion of the Theattenuator l is shown as a balanced variable .volume range. _ - While only a single rerecording channel has been disclosed, it is evident that this invention tenua'tor or potentiometer may be used as de is applicable to a multichannel rerecording sys sired. A portion of the'signal currents in the output of the ampli?er 3 are supplied to the ex 50 tem, such as a-stereophonic' rerecording system resistance network, but any‘other form of at pander II and, after suitable ampli?cation in vthe ampli?er ll,""are reproduced by the moni-' toring reproducer II. The control currents in the output of the attenuator 8 are also supplied tothe expander It to control the automatic ex 55 and that the control" current may be either a slowly varying direct current or a selected car rier current. 1 What is claimed is: , ' ‘ 1. In a rerecording system, a record medium ' 2 2,254,034 having a record of electrical waves compressed as to volume range and a control record of the degree of compression applied to the waves dur ing recording, means for reproducing and rere- ’ 3. The method oi! enhancing the amplitude of reproduced waves which comprises recording the waves modi?ed in amplitude, recording the modi ?cations made in the amplitudes ‘of said waves, cording said record of electrical waves, means 5 rerecording the record of said waves, rerecording energized by said reproduced wave for audibiy said modi?cations, arbitrarily changing the mag reproducing said electrical waves, means for re nitude of said modi?cations at desired times producing and rerecording said control record during rerecording without changing the pat and for controlling said audible reproduction and tern of said modi?cations, reproducing said re a manually variable attenuator in the channel for 10 recorded record of said waves, reproducing the rerecording said control record. changed record or said modi?cations, and con 2. In a rerecording ‘system, a record of waves trolling the reproduction of said waves by the modi?ed in amplitude, a record of the modi?ca changed record of said modi?cations to restore tions made in the amplitudes of said waves, a the amplitude variations of the original waves, pick-up ‘for said record of modi?ed waves, a re 16 and to enhance the amplitude variations in the corder associated with said pick-up, a pick-up reproduced waves. ‘ for said record of modi?cations, a recorder asso . HARVEY FLETCHER. ciated with said latter pick-up, and a manually variable attenuator in the circuit connecting said latter pick-up‘ and said ‘associated recorder. 20
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