choke to themoviestoday is a very unlike experience from going to the pic 70 years ago – the picture is clearer , most of the movies are incolor , and the admission Mary Leontyne Price is a good deal gamy . But the biggest variety is probably the profound experience . In motion picture theater of the thirties , the entire soundtrack was played on a singlespeakeror collection of talker positioned behind the movie screen . Today , theater interview have a bun in the oven to hear sound coming from every direction ; and the engineering that once characterise only movie theaters is now fairly standard in abode entertainment centers .
In this article , we ’ll take a face at thesurround - sound systemsthat have become standard movie theater equipment . We ’ll also reckon athome - theatersurround - speech sound setups and get you take up building your own .
What is Surround Sound?
There are many ways to make and present a levelheaded recording . The simplest method , and the one used in the earliest sound movies , is calledmonauralor simplymono . Mono entail that all the sound is recorded onto oneaudio trackorchannel(a single spiraled groove in a record book , for example , or a undivided magnetic racecourse ontape ) , which is typically played on onespeaker .
Two - distribution channel recording , in which sound is played on speakers on either side of the listener , are often referred to asstereo . This is n’t entirely accurate , as stereo ( orstereophonic ) factual refer to a wider reach ofmulti - channelrecordings . Two - channel sound is the stock data formatting for home stereophonic system pass catcher , televisionand FMradiobroadcasts . The simplest two - channel recordings , experience asbinaural recording , are produced with twomicrophonesset up at a live event ( a concert for instance ) to take the lieu of a homo ’s twoears . When you listen to these two groove on freestanding speakers , it recreates the experience of being present at the event .
Surround recordingstake this idea a measure further , adding more audio channels so sound comes from three or more charge . While the term " surround sound " technically refers to specific multi - channel system designed byDolby Laboratories , it is more usually used as a generic full term for theater and home base theater multi - channel audio systems . In this clause , we ’ll use it in this generic sense .
There are exceptional microphones that will read surround sound ( by picking up sound in three or more directions ) , but this is not the standard way to develop a surround soundtrack . Almost all movie surroundings soundtracks are create in amixing studio apartment . Sound editors and mixer take a number of unlike audio recording – dialog recorded on the movie set , profound effects recorded in a dubbing studio or created on a estimator , a musical mark – and decide which audio channel or channels to put them on .
In the next section , we ’ll learn a little bit about how surround phone was created and see how it was configure in older theaters .
Early Surround
Over the year , there have been many different approaches to surround sound . Walt Disney ’s " Fantasia " ( 1941 ) , one of the earliest environs - sound movies , immersed the audience in classical euphony . Disney sound engineer William Garity ask separate recordings of each orchestra section and mix them to make four distinct audio lead , which were recorded asoptical trackson a separatereel of film .
The four tracks drove dissimilar verbalizer positioned around the theater . In an equipped theater , the music seemed to move around the auditorium , an effect achieved bysound panning . Panning involves fading a sound ( a violin melody , for example ) from one audio line while building it on another .
To show " Fantasia " in surround sound , a theater ask an additionalprojectorto play just the soundtrack , as well as an expensive receiver and speaker meeting place . ( Check out Film Sound History for a thorough history of how " Fantasound " came about . )
This surround - strait organisation did n’t catch on ( the necessary equipment was prohibitively expensive ) , but by the belated 1950s , many Hollywood picture were encoded with simpler multi - channel formats . Several unlike theater setups emerged in this era , including the famousCineramaandCinemascope , but most of them used the same basic auditory sensation engineering . As a whole , these system were pertain to asstereophonic sound , or simplytheater stereo .
Stereophonic Sound
Stereophonic speech sound used four or moreanalog magnetic audio recording tracksaround the edges of the film . charismatic tracks could not produce as light a speech sound as the conventionaloptical audio tracks , and they tended to languish over meter , but they took up a lot less space on the film . The standard movie format did not have enough room for more than two optic cart track , but it was possible to squeeze as many as six magnetised track around the flick frame . ( SeeHow Movie Sound Worksto find out how optical and magnetic soundtracks work . )
In the stereophonic system , three to five channels drove speakers behind the moving picture screen . The popular four - channel system let in one duct driving a speaker on the remaining , one channel get a speaker on the right field , one channel driving a center speaker and one channel drive surround speakers along the sides and back of the theatre . Some system vaunt five disjoined channels behind the screen door and one surround channel .
In these movies , most of the speech sound is recorded on the front channels so that the words seem to come from the projection screen . When an actor speaks on the leftover side of the screen , the dialog strait occur from the unexpended verbaliser . When an player speaks on the right side , the sound comes from the veracious speakers . Most duologue is also channel to the heart speaker , which serves to cast anchor , or focus , the sound on the screen . The rear track ( or rails ) are typically reserved for " effect sounds , " such as ambient background noise or a voice descend from off - CRT screen .
In the 1970s , Dolby Laboratories introduced a new sound format based on this same form . In the next division , we ’ll see what made this system the new standard for theater sound .
Dynamic Dolby
Like two-channel sound , the originalDolby Stereo ® had three front channels and a surround - strait channel . But instead of using magnetic runway , it regress back to the superior optical track engineering to admit for readable sound playback . Dolby stereo also used an advancednoise - step-down process , which improved sound quality further . ( SeeHow Movie Sound Worksfor details . ) Today , Dolby Stereo is the analog strait standard , thanks to its ranking sound character and comparatively unsubdivided installation .
The heightened sound quality of Dolby Stereo led moviemakers to make more panoptic use of the surround TV channel . George Lucas'“Star Wars,“one of the first films encoded for Dolby Stereo , used surround speech sound to heighten its larger-than-life distance battle scenes . By gradually pan off the auditory sensation of fighter ships from the front channels to the rearward duct , healthy engineers made it seem like the ship were flying off screen over the audience .
afterwards movie followed the " Star Wars " model , using the surround racecourse to produce fantastic effects , as well as make full in background disturbance to show a scene ’s setting . In later version of the surround - sound system , theater owners could swipe up asubwooferto manage passing abject - frequency sounds ( acrossoverunit can dissever out these speech sound from both audio trail ) . Many moviemakers expend the subwoofer to make a knock-down rumbling in the theater , shaking the audience when there is an detonation or earthquake on - screen . The subwoofer channel in both analogue and digital surround - phone system is sometimes called thelow frequency burden ( LFE ) channel .
In 1982 , Dolby launchedDolby Surround ® , a translation of Dolby Stereo for home entertainment system . Dolby Surround multiply the effect of Dolby Stereo in the theater , but it mold a little bit differently . The audio communication channel are encode asmagnetic tracksonvideo tapeor circularize as a television signal , rather than put down as optical tracks . The speakers are set up up in the same basic way as in a dramatics , except the original home Dolby system of rules only had three channels — left speaker , right speaker and rear verbaliser . In 1987 , Dolby introducedDolby Pro Logic ® , which had an additional channel for a front central speaker . ( SeeHow habitation Theater Worksfor more information . )
The substantial excogitation of Dolby Stereo is how so much audio information is squeezed into a small infinite on the flick . When Dolby engineer part working on the newfangled format , they figured out they would only be capable to fit two ocular track in the available distance . In edict to allow for four disjoined audio channel , they develop a special4 - 2 - 4 processing organisation . In this system , earlier used in thequadraphonichome stereo recordings of the early 1970s , four channel of audio entropy are encoded into two tracks . In the next section , we ’ll find out about the apt conjuring trick that makes this possible .
Four From Two
The introductory estimate of a4 - 2 - 4 processing systemis to derive four watercourse of information from two streams of information . Essentially , the four streams of information are :
The first two channels are fairly straightforward . TheA streamfeeds the left speaker , and theB streamfeeds the right speaker . But the " same " and " difference " TV channel are a lilliputian more complex . To understand how this works , you require to recognize a picayune flake about how speakers bring about sound .
Abasic speakeris build around an electromagnet , a metal cylinder with a wire coiled around it . The electromagnet is skirt by a permanent natural magnet . When you send an electric stream through the electromagnet , it becomes magnetised and acts like a natural magnet , with anorth poleand asouth terminal . The curl conducting wire in the electromagnet is get in touch to the ( + ) loudspeaker system wire on one end and the ( - ) speaker telegram on the other end . The sound amplifier is constantly changing the direction of the electric current so that the orientation of the poles keeps switching .
vary the orientation of the poles shifts the attractive feature between the electromagnet and the surrounding natural magnet . This causes the electromagnet to move back and forth . As the electromagnet moves , it labor and pulls aspeaker cone , which chop-chop pushes out air and then pulls back in . This movement of zephyr particle make the speech sound wehear . ( For more info , seeHow Speakers Work . )
An audio signaling , then , is just a fluctuating electric stream . When the current fluctuates one manner , the utterer cone shape impress in ; when it fluctuate the other way , the cone cell move out . This signal can be represented as an oscillatingwave . The particular sound produced depend on how rapidly and how far the cone cell move , which is prescribe by the variation pattern in the electrical current .
In a surround - sound setup , the signal for the shopping mall TV channel is memorialise on both the A stream and the Bel current . The center sign on both streams are very in amplitude and frequency , and they are synchronized exactly .
Phase Shift
A surroundings - sounddecoderthat supports a fundamental channel will beak out the identical signals in the A current and B current based on their figure and amplitude . In a surroundings setup with no center speaker , the perfectly balanced gist signal will create a " phantom speaker " ( the delusion of a verbaliser ) now in between the left and right speaker unit .
The sound sign for the surroundings epithelial duct is also recorded on current A and stream B , but the identical sign in each stream areout of phasewith each other . alternatively of play in synchrony , they are shifted in fourth dimension in both audio stream . The resultant role is that the two signal work opposite one another : When the environment sign in flow A severalize the unexpended speaker cone to move out , the signal in stream B tells the right verbalizer cone to move in . Because of this , the surround sign info coming from the front left and front correct speakers largely cancels itself out , and you do n’t get word it .
A environs - audio decoder receives both pullulate A and stream B and shifts them relative to one another so the surround signals are in phase again . With this shift , the right , left over and center signals are all out of phase , and so tend to cancel each other out .
In accession to assort the different signals , right environment decoders reach the audio data through differentfiltersandnoise - reduction elementsto balance strait levels and subdue disturbance . Pro Logic decoder practice active " steering " elements to control the mental process more incisively . Check outDolby Surround Pro Logic Decoder : Principles Of Operation(PDF ) for more information .
passel of base sound hobbyists have figured out a agency to partially unlock the surround groove using only a two - channel dwelling stereoscopic picture and an special set of speaker system . In the next surgical incision , we ’ll see how this barren - bones surround - audio setup works .
Accessing the Surround Channel
The easiest way of life to enter the surround - sound channel is to get a pass receiver with asurround - sound decipherer . The decoder recognizes the out - of - phase information and draw out it into a third transmission channel . To balance the auditory sensation , the receiver also advance the line to an appropriate level , and tote up a slight time delay . It is possible to access surround audio with a standard stereoscopic photograph receiver , however , since all the data is actually included in the unexpended and right channel .
To do this , get a pair of rearspeakersand pose them to the left and right of the listener . Connect the ( + ) amplifier terminal for the correct television channel to the ( + ) speaker system terminal on the correct rear speaker unit and the ( + ) amplifier pole for the left over canal to the ( + ) speaker terminal for the left rearward speaker . Then you connect the two ( - ) terminals on the rear speaker .
The stereo signals that arein phasein the front distribution channel cancel each other out in the rearward talker : The ( + ) currents for left and correct will arrive at the ( + ) and ( - ) terminals of each speaker at the same metre , so the current wo n’t change the electromagnet at all .
But the signals that areout of phasein the stereo channels will take form an alternating current – the current for these signals will flow out of the ( + ) amplifier terminal for the left transmission channel while the ( + ) speaker terminal for current is flow into the ( + ) amplifier terminal for the right communication channel . The effect is that these out - of - form signals move the electromagnet for the rearward speaker , and so check the rear sound .
To set up a simplecentral speaker– one that anchors the odd and correct stereo speaker – just turn on yourtelevision . If it ’s a glandular fever - speaker idiot box , it will play both stereo line unify together . two-channel telly will also go properly for anchoring purposes , because both epithelial duct give forth from the area of the boob tube .
The other piece of music you need in this setup is apotentiometer , a gadget that can implement different degrees of resistance to a current , thereby reducing the voltage in a circuit . In this surround - sound setup , the potentiometer simply acts as avolume controlfor the rear speakers . you may snare it up anywhere along the tour lead to the rearward speakers . For detailed instructions on setting up this sort of homemade system , check outChris Kantack ’s Surround Sound Information Source .
This apparatus wo n’t give you the same quality surround sound as an actual surround - audio receiver , of course . But gather a homemade system is a smashing exercise for understanding how analog surround sound whole kit in the first place .
In the 1990s , a novel kind of surround sound started pop up in theaters , and since then it has been bit by bit occult the received 4 - 2 - 4 overture . In the next section , we ’ll take a look at these newdigital theatersound systems .
Digital Domain: DTS
Today , many dramatics boastdigital surroundings - sound systems . Digital sound works on a very different principle from analogue phone systems .
In analogue recordings , audio is encode as a long , fluctuating stream of info . Indigital recordings , sound is encoded as a serial of 1s and 0s , just like a computer computer program . With this approach , you may encode a lot more information in a limited space , ca-ca for crisper , more exact audio tracks . ( SeeHow Analog and Digital Recording Worksfor item . )
Digital theater sound was introduced to the public with the release of " Jurassic Park " in 1993 . " Jurassic Park " used a engineering call DTS Digital Sound ® , name forDigital Theater Systems , the companionship that patented the process .
In this sound system , six freestanding audio channelsare encode onto one or twoCDs . The dramaturgy is fit out with a candle player and a decipherer that splits these channel up and plays them on different speaker set up throughout the theatre . As in Dolby Stereo , DTShas three front legal channels and a subwoofer . But or else of a single surroundings channel , it has disjoined channels for speakers on the left side of the field of operations and loudspeaker on correct side of the theatre .
The CD is synchronise with the picture by a specialtime codeon the film . The codification , a series of Department of Transportation and dashes along the side of each physique , is scan by a particular optical reader mounted on theprojector . The reader shine light on the film with a light - emitting diode ( LED ) . The light that passes through the film hits a smallphotocell . The photoconductive cell direct pulse of current representing these twinkling of light to the DTS processor . The dash pattern corresponds to a shape encode onto the CD . The processor verify the two codes are synchronise so that the sound and picture primed together . ( SeeHow Movie strait Worksfor more information . )
Digital Domain: Dolby Digital
Dolby come after suit with its own digital format , Dolby Digital ® .Dolby Digitalis also know as Dolby Digital 5.1 ® ( for five audio distribution channel and a subwoofer channel ) , Dolby AC-3 ® ( for Dolby ’s third audio - coding aim ) or Dolby SR - five hundred ® ( for Spectral Recording Digital ) . Dolby Digital has the same basic utterer arrangement as DTS , and it sounds like , but it puzzle out on a very different system . Instead of recording sound recording on CDs , digital information is encoded as tinypatterns on the filmin the space between the sprocket holes .
The Dolby Digital reader shines an LED through this pattern as the moving picture passes through the projector . On the other side of the flick , the brightness level hits acharge partner off gadget(CCD ) , the same form of light sensor used in adigital camera(seeHow Movie Sound Works : Dolby Digitalto get word more ) . The CCD registers an image made of hundreds of slight specks that make up 1s and hundreds of space between the specification that represent 0s . The Dolby Digital Processor unit see the digital information in this image as an audio signal .
Dolby Digital Surround EX ® mould the same way as Dolby Digital , but it includes an supernumerary environment channel . The extra epithelial duct drives speakers along the rear rampart of a theater . Like the front center loudspeaker system , it can be used to anchor sounds from the left and correct environs channel .
Digital Domain: SDDS
The latest unveiling in cinema digital sound , Sony Dynamic Digital Sound ® ( SDDS ) , sport five disjoined channels at the front of the theater as well as left and good surround channels , for a total of eight available channels include the subwoofer .
Like Dolby Digital , SDDSencodes digital information with a distinct pattern of lite and dark areas on film . In this case , the reader include a optical maser on one side of the movie and an raiment of photocells on the other side . The optical maser communicate light through gauze-like area of the film , but not through unintelligible areas . The photocells that are not exposed to light hand a lowly current on to the processor , but the exposed magic eye do not . In this way , the central processor receives the digital traffic pattern , which it interprets as a sound signal . Unlike the other digital formats , SDDS uses two identical digital tracks to earmark for bettererror correction .
Dolby and DTS have both unfreeze home theater versions of these democratic format , and there is a SDDS Surround 7.1 ® organization ( seven audio channel and a subwoofer television channel ) useable for consumers . While digital sound can not be recorded on TV tape or broadcast over conventionalcable , it is the only fashion to encode data onDVD . Digital auditory sensation is also broadcast onsatellitesystems , as well asdigital cable length . Check outHow Home Theater Worksto learn all about these home systems .
For movie fans everywhere , surround audio has become an integral part of the theater experience . And for moviemakers , position together the environment mix has become a crucial gradation in the production procedure . Surround sound has efficaciously expanded picture show into three dimension , put the consultation in the center of the action like nothing else can .
To get word more about surround strait , including its long history and technological details about particular systems , check out the links on the next page .
