B.B.C NEWS STORIES

Nelson Evening Mail, Volume 76, 19 June 1941, Page 6

8.8. C NEWS STORIES

HOW THEY ARE RECORDED “WE ARE NOW TAKING YOU OVER TO . . . Listeners to the BBC news bul- ! letins often hear the announcer say | somethin? like this: ‘*Our observer, Robin Duff, visited Dover this afternoon. Here are his impressions, recorded on the spot.” How the observer’s impressions are recorded and later broadcast to the world is described in this article, written by a senior member of the BBC’s engineering staff. A vital task of broadcasting is to give an accurate and vivid impression of contemporary life and current events. The most direct way of doing this is by means of sound pictures which combine the actual sounds of events with the voices of the men and women taking part in them. Sometimes this can be done by roving microphones, connected by telephone line to a studio centre, but the most interesting topical ! material is sometimes to be found at j places remote from telephone lines or |at times unsuitable for broadcasting. It must then be collected by means oj a mobile recording unit. Before describing the activities oi the mobile units in wartime, let us look at the equipment itself. It is of twe kinds—a heavy type mounted in a large van and a light portable apparatus carried in a saloon car. Each of these has its special uses; both make records in the form of discs which are somewhat similar in appearance to ordinary twelve-inch gramophone records, but consist of a coating of special cellulose varnish on a base of aluminium. Tl*>y are ready for playing as soon as the record has been cut, without any of the elaborate intermediate processes involved in making ordinary records, and each disc can be played twenty or thirty times before it becomes noticeably worn. The recording machines are similar in principle to those used in the disc-recording rooms at BBC studios. Electric currents, corresponding to the sound waves picked up by the microphone, cause vibrations of a recording stylus which cuts a wavy spiral track in the varnish Dn the surface of the disc. The spiral notion is obtained by causing the recording head which carries the stylus to move slowly across the surface of he disc while the latter is rotating on he turn-table. When the disc is Dlayed. currents similar to those which ■vere applied to the recording cutter are Droduced by the vibrations of the leedle in the gramophone pick-up: ifter amplification these currents can ?e made to reproduce the original sound hrough a loudspeaker, either directly >r through the medium of -wireless ransmissior. A mobile unit of the heavier type ronsists of a motor van, weighing about ;ix tons when laden, the body of which s divided into two compartments. One •ompartment is acoustically treated so is to form a small studio suitable for peech. The other contains two sets if recording equipment (so that a coninuous recording can be made by passng from one turn-table to the other is each disc is finished) together with he associated amplifiers, the controling and switching equipment, and the •attery-charging plant. Recordings an be made either of speech from the nicrophone in the studio compartment, r of speech or other sounds picked up >y other microphones outside the van nd connected to it by cables. The an can work away from its base, if lecessary, for several weeks at a time nd, since the equipment is all operated rom batteries which can be charged I rom the engine of the van, it is selfontained and independent of electric upply mains. The size of the van lakes it possible to accommodate the lost complete technical equipment for ontrolling the programme and checklg the accuracy of the recording, and Iso to employ the most robust and onvenient form of recording apparatus, ’he turn-tables can be made level by ydraulically operated adjustments so iat recordings can be made when the an is standing on a slope. The speed f the turn-tables can be accurately djusted, and gramophone pick-ups and loudspeaker are provided for reproucing sound from the records when ecessary. GETTING THE NEWS Although these heavy recording vans re well suited to many kinds of reording work, experience has proved iat a lighter form of mobile equipment ; also necessary. In 1938 the BBC ews Department felt the need for a lobile unit which could travel rapidly ) any part of the country, obtain a >pical news story, and bring the reirds back the same night (to Lonon or any other BBC studio centre) to e included in the news bulletins. The pparatus had to be sufficiently compact > fit into an ordinary saloon car, light nough to be carried into a building or ■t up in an aeroplane, and robust lough to withstand travelling over bad )ads at high speeds. Although it ould normally be used in the car, the pparatus had to be readily movable » that is could be carried by hand to laces to which the car could not be iken. It had also to be independent • external power supplies and to be litable for use not only as a recordig unit, but also for direct outside roadcasting work where suitable post Tice telephone lines were available to irry a “live” broadcast. It was also scessary to provide facilities for reroducing a recording and connecting le output to a telephone line where lere was not time to bring the records i a studio centre. The equipment had so to fit into the car without any odification of the standard bodywork id without‘fitting any special mountgs in the car. The present design of the light reirding unit is the result of a study f the problem by 8.8. C. engineers. is not possible for such a compact nit to provide all the advantages of le heavier one—it cannot make a mtinuous recording lasting longer 1 lan the duration of a single disc about four minutes), and it lacks ' iany of the facilities and refinements hich are provided by the heavy van.j ut where speed is essential it has a :eat advantage, because the saloon ir is not subject to the statutory ieed limit of 20 miles an hour, hich is imposed on the large van; oreover, it can be manoeuvred more isily in narrow streets and parked i more restricted spaces. THE RECORDING APPARATUS The apparatus consists of three main parts: the recording machine, the amplifier, and the power supply unit. The recording machine contable, the cutter-head, and the tracksists essentially of a heavy turning gear which gives the correct spiral form groove. The turntable is driven by an electric motor operated from a twelve-volt accumu-j lator battery. The shaft of this motor! carries a small rubber wheel which is in contact with the rim of the turn-table, so that the latter is driven smothly and evenly at a considerably slower speed than the motor. The same motor also drives the tracking mechanism; this includes a lead-screw which is supported behind the turntable and extends across the width of it. As it j rotates, this lead-screw carries a rigid arm slowly across the turn-table from the outer edge of the disc to-) wards the centre; to the end of this

arm is attached the cutter-head which looks very much like an ordin ary gramophone pick-up except tha instead of a steel needle there is ; steel cutter, the edge of which i accurately shaped to carefully calcu lated angles. The action of the cur rents which are passed through th cutter head is to vibrate the cutte from side to side and so produce ; waviness in the spiral groove corres ponding to the sounds which are be ing recorded. The weak currents produced by thi microphone are applied to the inpu of an amplifier which gives an out put sufficient to operate the recordinf cutter. This amplifier has three stages of amplification and uses the principle of ‘negative feed-back’ tc neutralise any distortion which maj arise within itself or in the recording head. The first section of the amplifier is the same as that usee for ordinary outside broadcasts, anc it may be employed for this purpose by switching off the output stage anc connecting the telephone line to the terminals provided. In this condition the amplification is sensibly the same for all frequencies from 50 tc 8000 cycles per second, i.e., for al! the notes on a piano from the lowesi G to more than an octave above the highest note. On the top of the amplifier there are two input sockets —one for connecting a moving-coil microphone, the other for connecting either the electrical pick-up for reproducing recorded discs or a threechannel microphone mixing unit; the latter is used for selecting or combining the various outputs when more than one microphone is used. On front of the amplifier there are mounted a peak programme meter and a controlling potentiometer, or volume-control, to ensure that the correct volume is aplied to the recording head throughout the recordings. The recording machine is provided with two main operating levers—one to engage the tracking mechanism to start the traverse of the cutter across the disc and the other to lower the cutterhead on to the blank disc at the moment when the recording is to start. Provision is also made for varying the depth of the cut. the angl» of the cutting stylus, and the speed with which the recording head moves towards the centre of the disc. This last adjustment determines the pitch of the spiral ti'ack, i.e. the number of grooves per inch which appear on the disc. During recording, a brush moves across the face of the disc and sweeps up the thread of ‘swarf’ which is cut from it, and which is thus prevented from becoming tangled round the cutter. The sweeping movement of the brush is derived from the clamp which holds down the centre of the disc, through a small rubber-tyred wheel which is fixed eccentrically on one end of the brush holder. The brush can be removed and an electrical pickup plugged into the same socket for playing back the recorded disc. When the pick-up is plugged in, the necessary electrical connections to the amplified are made automatically. ACCURACY OF SOUND REPRODUCTION To obtain faithful reproduction of the original sounds the speed of rotation of the turn-table must remain constant at the standard rate of seventy-eight revolutions per minute. The speed is constantly checked 'by means of a “stroboscope,” which consists of a number of holes drilled in the outer rim of the turn-table and of a neon lamp which shines through these holes from beneath. This lamp is supplied with alternating current from a small specially designed oscillator mounted in the case of the recording machine. The spacing of the holes in the rim of the turn-table is related to the rate of flashing of the lamp in such a way that the light appears to remain stationary when the turn-table is rotating at the correct speed, but to move round the turn-table in one direction or the other when the speed is too fast or too slow. The power-supply unit contains a motor-generator and smoothing circuits for the high-tension supply to the amplifier, the controls necessary for the low-tension circuits, and a variable resistance for regulating the speed of the turn-table. This unit is elastically mounted to reduce vibration and supplies direct current at four hundred rolts; it is driven by the accumulator pattery. There are two small circuit areakers, one to control the motorgenerator and the other to control the 11-ment supply to the amplifier; these switch off the current £ an accidental short circuit occurs. In order that the equipment can be issembled and put into operation with he least possible delay, the connections jetween the various units are made by r eans of interconnecting cables fitted vith plugs and sockets, the cables being :arefully screened, where necessary, o prevent electrical interference. The vhole of the equipment opei'ates from wo batteries, each consisting of five | WWWLWiWWVWW^W

[, nickel-iron accumulator cells. One, - of the batteries has a capacity of a I t hundred and twenty ampere-hours and I a th ? other of eighty ampere-hours, the 1 s supply for the filaments being taken '• - from the larger battery. The turn-' - table motor and the motor-generator j e take their supply from the t”'o batter- ' r ies connected in series. 1 The equipment is normally carried! -in a fourteen-horse-power saloon car. j - The supply unit stands on the floor j behind the driver’s seat. The amplifier j 2 rests on the top of it and the recording j t machine stands on the rear seat of the ! . car. The batteries are carried in the i luggage boot and their connecting i cables run through the back of the i rear seat. The luggage boot also con- ) tains cable drums holding up to four r hundred yards of screened microphone . cable, telephone sets for communication » between the microphone points and 1 the recording engineer in the car, the l three-channel mixer, loudspeakers, a i I telescopic microphone stand, and a kit lof tools. There are also head-phones > for checking the programme when it is . not convenient to use a loudspeaker. RECORDINGS AT REST OR ON THE MOVE - When the records have been made, • they are either taken to one uf the BBC ■ studio centres or played back in the ■ car itself, the output being connected 1 1! by a telephone line to the studio cen- ! tre. Lines used for the transmission of a programme are specially tested by the lines engineers of the BBC and I : “equalised” so that they respond equal- ; ly to all frequencies within the range i necessary for the faithful transmission of music. For reproducing recordings A in this way, the car is taken to a tele-1 ' phone exchange where connections can be made directly to the telephone lines, j In order that the recording may be | started at precisely the right moment to fit into the broadcast programme of which it is to form part, it is necessary ] for the recording engineer in the car to hear the cue which is the signal for him to lower the pick-up on the record and ‘“fade up” the output. This cue < may either be taken on another tele- \ phone line from the studio centre, or it 1 may be heard on a portable receiver 1 tuned to the programme in which the j ‘ recording is to be inserted. In the ■ latter case, the recording engineer will | , hear the announcer say: “We are now j ( taking you over to .... to hear our j < observer, 'whose commentary has been i 1 recorded earlier to-day”—or the com- j i mentator may speak directly at the j 1 microphone, starting on a signal from ! ' the engineer, to link together the var- j J ious recorded items into a connected j s story. Each section of the recording i J is then played over at the appropriate ! points in the observer’s talk. Smooth presentation of this type of programme demands close co-operation and com- j plete understanding between the re- t cording engineer and the programme 1 staff both at the outside broadcast point t and in the studio centre. Although the equipment is normally operated from F the car while stationary, recordings £ have been made while on the move— _ following processions, in aeroplanes in s the air, in express trains, at sea and jeven in a submarine diving. e THE BBC’S RECORDING UNITS ON j. ACTVE SERVICE J Since the beginning of the war, some F of the mobile recording units and the! men who use them have seen danger-1 ous and exacting service. On the!], declaration of war one of the saloon j cars was loaded on to a cross-Channel I p steamer at Dover. It passed through ! fj the French customs without delay, and was driven to Paris, where it was left t! for a time in a deep garage ready for 1 action. When BBC war correspon- c dents were allowed to accompany the fc B.E F. early in October 1939, the BBC c unit, consisting of a commentator, a v programme official, and an engineer t tcok possession of the car. Accommodation was provided at G.H.Q.. and a an attic was made into a small studio. c During the winter, the extreme cold b made it difficult to cut good records, partly because frost patterns formed on * the blank discs and affected the sur- ° face, and partly because the liquid in the batteries was affected. Temperatures as low as 40 degrees Fahrenheit below freezing were encountered, and the engineer even had to take the discs to bed in order that they might be in good condition for cutting next day. One of the many programmes re- tl •orded by this unit took place in the tl Vtaginot Line, where the apparatus sj was taken out of the car and set up on _ a truck on the miniature railway system which ran through the under- ir ground forts. Another was the record- T ing of a march past of the band of the ti Chasseurs Alpins, which was taken at fc six o'clock in the morning in a blind- tz ing snow-storm in the Jura Mountains, u: Many of the broadcasts from France c< were relayed through the Lille station w of the French Post Office, where the j B French engineers did magnificent work | oi