|
|
Beyond the stereo sound Part 1 : Multi-channel sound
Aug 8, 2003 - by Franck ERNOULD
Nothing new under the sun : the stereo sound shows its limits and does not let you be surrounded in a sonic space. In front of such a sad fact and knowing the failure of the quadraphony, two techniques are competing : on one hand, multi-channel broadcast with the 5.1 leader and on the other hand a psycho acoustic approach which consists in creating three-dimensional effects through a pair of speakers. In the first part, we'll deal with multi-channel techniques.
Since human have lived on the Earth, we‚ve used our 2 ears to hear. Hundred years ago, our ancestors were listening to gramophones in mono sound, then to cinema and radio. The stereo appeared in the 60's. Now there is 5.1. Sony only delivers 7.1 for very big theatre rooms for now !
| Acoustic stereo | |
 |
All scientists agree on the fact that we are granted 2 ears. Those efficient captors and the treatment that the brain makes of their signal enables us to locate a sound in our whole environment : left-right place, and also back-forth and up-down. Thus hearing takes advantage in front of seeing which is frontal. When coming back to primitive ages, everything you can't see is potentially dangerous. Therefore our brain sets up in alert mode as soon as it perceives a sudden noise coming from the back. The reflex is that we turn back to check about this noise.
This is something to take into account when mixing in surround mode !.
For ages music used acoustic instruments emitting energy towards every directions, reflecting on walls when you are inside a room. Our brain manages to locate the players in the room space, evaluate their distance (ratio direct field/reverb field). Clever music has used spatial effects far before ProTools plug-ins : let some musical phrases go from one instrument to another, from left to right for instance. Right from 16th century, some pieces were written for two church organs or two choirs placed opposite from each other inside a single nave. Later on as "clever music" is allowed to be played outside church or princial courts some concert hall are being built so that they "sound" good : length and reverb colour for example, what we would call architectural acoustic nowadays..
The creation of the phonograph during the late 19th century makes an end point to the time when any sound event should be performed live. As the machine is quite complex to build, it was not planned to double those difficulties only because we got two ears ! Did you know that phonographs have got no microphone neither speaker : the acoustic energy is received by the pavilion and is transmitted to the throb by a mechanical way, then the wax is engraved within the depth dimension - the same happens the other way while playing. The subtleties of the sound picking or the playing are not taken into account : everybody stays around the pavilion, the soloist is in the front, and turning the crank.
| Cold shower | |
|
With the creation of the more sensitive microphone, the sound taking can be finely performed : this is the age of electric recording. The new radios uses intensively that captor, which was first made of coal then ribbon, from which we amplify the signal with triodes, also a new electronic component. Meanwhile an optical technology has been used since 1927 to record sound modulation on the layer, but it is using the same kind of microphone so you get it hard to distinguish the directivity... Better speaking loud and clear if you want to be understood !.
From 1927 (what a coincidence !), some Mr Neumann once presented a strange microphone the shape of a bottle : the CMV3. There was no other more sensitive microphone, and the recording resolutions were far above the known techniques at this time such as direct burning on a 78 rounds disk without assembly. During the 30's, an English engineer called Blumlein thought about stereophony. He applied numerous patents, about sound taking with 2 microphones for instance. At this time, he is the only one !.
The creation of the magnetophone spreading worldwide during the 50's is changing the way recordings are carried out. The new 'support', a magnetic layer, outweighs in quality anything that has ever existed till then. In other words, the grain of the records made from the Neumann newly created U47 or C12 remained original. Double magnetic head are soon being developed : the idea of stereophony makes its comeback and sign the birth of "high-fidelity". After many attempts, the 2-channel burning on the sides of the furrow is being standardized on disks which are 20 to 30 minutes lenght per side. Sound engineers believe in this technique and rush on the process. Disk manufacturers are not so convinced by this technique : "During the mid 50's, 'official' recordings were monophonic" says Bruce Sedien. "We were experimenting with stereophony, but it might appear surprising to us that disk labels and show business 'dealers' did not believe in stereophony at all. They were trying not to encourage us to use it, for example by not paying the stereo magnetic tapes we were using at the same time - the recording stuff was located in another room. I was even told once: 'Why stereophony ? I don't take my shower with two pommels !'. If you say so...". Some people were experimenting artificial heads having 2 microphones, more or less sophisticated, but unless you heard on headphones, results were disappointing.
| On your two ears | |
|
So now the stereo disks are coming onto the marketplace. It will take ten years before it conquers the market : don't forget that the first Beatles or Pink Floyd were mixed in mono - the fans using their 33 rounds Teppaz did not deny them... At the end of the 60's starts the golden years or "high fidelity systems", which soon becomes the symbol of the consuming market. The frequency modulation appeared roughly at the same time as the micro furrow disk, and provides some stereo programs too (only France Musique - but none of the private radios until 1981, because of its monopoly)..
The stereo tape and the radio player, sometimes granted with a system that widens the sound rendering, reach a known success as well. In the meantime of those evolutions, the cinema stayed monophonic, which did not prevent some producers from making sophisticated and precise sound tracks, recorded with some Nagra microphones. Some short experiments were carried out to go further and try to put sound on several channels : the first ever was a cartoon realized by Disney right in 1941 : "Fantasia". They tried to „fill" the super panoramic screen of the hollywoodian production in the big shows of the 50's : those movies are taken on a 70mm layer and played with 6 magnetic tracks put on the border of the film..
At last in France, Jacques Tati mixed "Playtime" in stereo in 1967. But that was still experimentation : no standard of production was raising yet, and very few theatres got those "improvements". Let remember the Sensurround¨ process used in the "Earthquake" movie, which consisted in putting a lower speaker under each seat so that the watcher feels better the vibrations. So sorry for the 7th Art fanatics, the sound of cinema was way behind the "musical" sound for average people at the beginning of 70's : still monophonic and optical - a technology that quickly cut off the high sounds with a limited dynamic and also very sensitive to the parasites caused by the physical damages of the films when played hundreds of times..
| Sound quadrature | |
|
Following their success at the beginning of the 70's, the high fidelity system producers launched a new concept : the quadraphonic sound. This was the time for multi-tracks recorders (even with classical music !) and the sound must be taken at the near source which makes it impossible to pick the ambient sound in small studios usually. Sending the channels towards two or four buses is no real problem : all disks are going to be mastered on 4 channels now. No problem for the recording of masters either, 4-tracks recorders are widespread at the time when multi-tracks recorders deal with 6 times more channels. Taking into account the fact that the black disk is the only quality media by then, the engineers are thinking about this delicate problem : how to put 4 channels in a furrow which can hardly handle 2 channels, burnt with a 45 degrees bias ? They thus invented some matrix systems, combined with techniques allowing very high carrying frequencies (40 to 50 KHz), modulated by rear channels, then mixed with front channels which are burnt normally to keep the compatibility with stereo systems. People were urged to equip themselves with 4 speakers and a 4-channels amplifier, and first of all a sophisticated head player which was therefore expensive. Let be aware : results were not as good as expected. "At the studio, everything was fine, the 4 tracks mixing was impressive. But by listening the quadraphonic disks from the market, things were getting worse...", reminds Alan Parsons. "In order to get a good result, the burning and the pressing had to be very precise, the playing head perfectly gauged and build in order to support over 40 KHz frequencies, and some well calibrated decoding circuitry. Else we had the impression of an always back and forth out phasing !". Above all, the manufacturers did not agree on a single standard (a known song), strange signs such as QS, SQ and Stereo 4 finally brought confusion in people's minds... and the quadraphonic sound disappeared as quickly as it had come. Few dozens or masters remain in the cellars, but the matrix techniques have not been lost (see Dolby article).
| Enlighten systems for dull rooms | |
|
The Dolby laboratories, famous for their noise reducers for professionals (A) and wide public (B), get further with the Dolby Stereo in 1978. That system enables 4 sound channels on a mono compatible optical track : left, centre, right, ambiance matrixed in 2 channels Lt and Rt. The noise reduction technique used - A, then SR at the end of the 80's - raises sharply the dynamic range. Applied on movies such as "Stars War" or "Apocalypse now", the process became the first multi-track standard in the world. According to Dolby there are nowadays "9340 Dolby encoded films". According to the actual criteria, those performances sounded limited : band width, dynamic..., not to tell about the ambiance track cut off at 6 KHz. The sound immersion felt by the watcher is a fantastic feeling at least at first (except for the few privileged people who attended some electro-acoustic multi-channels concerts mixed from the early 1960), with no comparison with any pure music. At the mixing stage, the rules are strictly defined : voices in centre, the other stuff on the right and left, and few things in the surround. A Dolby adviser helps the sound engineer when making his first mix work in such a format, advices him one or two things, forbids some others... At the production level, the Stereo Dolby is quite restricted in its possibilities. 10 years later, that technology has been commercialised for a wide public with the name "Dolby Surround". The selling figures are flattering !.
Nevertheless, although it started poorly, the cinema sound was suddenly ahead of the music sound. Few years later, the CD popularises the digital technology so that Dolby going to release the Digital Dolby soon: some digital information 10 times compressed are stored as "pavement" between the holes of the film - there was no room left else where ! -, leaving untouched the traditional Stereo Dolby tracks. In the movie theatres this is ecstasy : 6 channels, an amazing dynamic, a sub-bass channel, a real stereo ambiance... The success is there : nowadays, almost 1800 movies are mixed with this format and 20000 rooms are equipped in the world... even if the decibel quantity often primes over the quality ! In the cinema studios, there is a hardware profusion : automation consoles, digital multi-tracks, high quality speakers - the THX warnings are high about them - and as much effects as in a music studio..
| Still further | |
|
The perfectionist film producer Steven Spielberg was not much satisfied with Dolby's work. In order to give the expected weight to the steps of the dinosaurs in Jurassic Park, he chooses a new "weapon" called DTS, standing for Digital Surround Technology. That other American 6-channels standard was partly inspired by the French team working on LC concept, one of the members even joined the DTS company..
The mixing format is the same, but the compression is less drastic : about 4:1. But due to their overweighed amount, the data must be put elsewhere than on the band, precisely on a CDROM which is played synchronously with the film projector, referring to a time code written on the film layer. Thus the DTS technique is launched on a movie that exploded the turnover in the world. This technique is widely used in movie theatres in the USA. So the engineers were urged to turn their knowledge into a "musical" version... Indeed, people in the show business start to put themselves into question. Original soundtracks compositors are leading : when the movie is 5.1 mixed, the music must be 5.1 mixed too ! Sometimes the adaptation is not obvious, says Didier Lozahic, from Zorrino studio : "On the soundtrack from "The fifth element", I could let my imagination work, especially in matter of putting the instruments on the different channels. I suggested to Eric Serra, who was thinking about "improved stereo", to place some sound only in the surround channel for instance. The results struck him !". Meanwhile, some artists started to think straight "5.1". Thus Alan Parson mixed "On Air" in 1996 both in stereo and Dts. Unfortunately very few people could listen to the Dts version : Dts decoders for CD players are seldom ! At the same time, a campaign for remixing in multi channel some known disks was launched by Dts : Allman Brothers, Brian Wilson, Eric Clapton, Joe Cocker, Moody Blues, Paul McCartney, Eagles or Steely Dan, all remixed in 5.1. But for the same reasons - getting and plugging a 6 channels decoder that is useless for anything else is going to be rejected by people -, those albums won't take the attention of the mass. Furthermore, even if they are disguised into audio CD so that they can be played on any CD player, it was impossible to play them without the decoder - you can hear some unpleasant white noise. So much handicaps while the DVD is coming !.
| Audio or video ? | |
|
The Digital Versatile Disk appeared in the middle 90's and was a unique phenomena in the history of disc recording: it is merely the first time that video and sound lay on the same disk. The 12 cm disc with 2 sides, with 1 or 2 layers was first designed for movie recording : it is called Video DVD and is likely to succeed to the VHS in the United States (American people don't use it much for recording). Then some variation of the DVD appeared, while some others are still being developed. There are for instance the DVD-ROM and Audio DVD. In a word, the DVD can handle anything ! But talking about the sound, what is the difference between a video DVD and an Audio DVD ? the answer is simple : in the former case, the data is compressed (Dolby Digital, Dts or MPEG) as video needs lots of room, constraints that can be overridden in the latter, due to the amount of available space. When you want to use the DVD as a multi-channel support, you are able to work with PCM 48 KHz on 16 or 20 bits on the six channels owing to the high bit rate. Things get worse if you want to work at higher resolutions or frequency sample, which an actual trend. There is no problem if you use stereo only, even in 24 bits, 192 KHz ! The Audio DVD specifications are put now and then, fixed and then put in balance again. Sony/Philips have brought confusion with their seductive Super Audio CD based on the DSD process (one bit sampling at 2,8224 MHz rate), while assuring an upward compatibility with the Audio CD : it has a normal layer, and a layer with DSD format on the same support. So now we've got 2 concurrency formats which both handle high definition and multi-channel sound, usually 6. Most astonishing thing is that we hardly know what shall be put on it musically speaking, that is to say without any link to the pictures... Precisely, no trend seems to come out. On live recordings rear channels reproduce ambience premix which were captured by several microphones placed everywhere in the room - results can be impressive like on Bazik DVD, which we were allowed to hear at mix level, or stranger, on a rock concert DVD on which a guitar was sticking playing in the rear channels. Maybe the guitarist had arrived late and stayed outside while playing anyway according to the music on stage ?.
| Colorization and 5.1 | |
|
As far as studio albums are concerned, nothing pops out as we said. Apart from speaking about centre, front and rear, do we have to use the subwoofer ? "It may be useful to hear Spielberg's dinosaurs but not music - we use it so that those who have bought a 5.1 system won't be disappointed saying that this huge thing is useless" says Bob Ludwig. Has the singer's voice to be in the centre, or does it stay in the left-right speakers ? In this case, what are we putting in the centre ?.
So many questions to which anyone can answer. As concerts are often filmed, they will probably be the biggest selling part of the real Video DVD commercial debut - the Eric Clapton "Unplugged" has thus become a classical demo, despite a Dolby Digital compressed 5.1 sound which is likely to lose a bit of subtlety. Are we going to see a campaign of 5.1 remixed concerts that were already released in stereo for long, Yves Jaget is mitigated : in order to be impressive and to avoid a "plated" aspect, the multi-channel mixing must be designed and assumed right at the beginning at the conception level : scene setting, sound settings, special effects, some exaggeration. Some styles are more ready than others". It will be tempting for producers to remix the most famous albums into 5.1. But it sounds a bit like colouring some old movie... This is a process in which morals must prevail, this can be done successfully provided that it is carried out by the primary sound engineer (for instance, Elliott Scheiner in "Gaucho" from Steely Dan - Bob Ludwig himself find it excellent in 5.1 - a reference as we know he had mastered the stereo version). The remix might also reveal to be a betrayal - indeed we remember listening to some singles compiled on DVD from Sting or Suzanne Vega, remixed for demo by anonymous sound engineers, on which all the personality put in the stereo mix by Mitchell Froom or Hugh Padgham had disappeared. But who would not do anything to give a new commercial life to old masters ?.
| The bill, please | |
|
Studios that would like to adopt 5.1 have got a pretty heavy bill... The acoustic design must be re draw : before that the energy was coming only from the front (where are the 2 stereo speakers), now 5 speakers literally surround the engineer. Absorption, reflexion control... everything is different. Also the place of a subwoofer in the sound system may be tricky to solve, as well as the changes to bring on the mixing console (specific hearing grid, such as StudioComm or Adgil). Finally the bill is minimum 15240 euros in the best case. At worst, the whole cabin has got to be made again. Notice that except for the Sony DPS-V55 and the brand new DRE-S777 having surround optimised programs, no manufacturer released any "5.1" reverb. It would surely be a success though, while even home studio consoles (see the Ramsa trial in this issue), sound cards and amplified speakers for computers have got the 5.1 format... For grand public, it is the same : within the over demanding market the arrival of surround sound is the up coming occasion to sell speakers and tuners-amplifiers to already equipped families but who own only stereo. Since VHS and CD, grand public almost rejected everything : DAT, DCC, LaserDisc, S-VHS... MiniDisc was accepted, but smoothly. It is difficult to foresee the surround fate.
| The wireless world is yours | |
|
TV producers already think about 5.1, so tells Frank Fradet, sound engineer to the SFP : "I think that the main purpose will be in sport : to re create the ambience of a football match platform for instance. It is a difficult ambience to work with : no really identified source but some kind of homogeneous hubbub even in an open stadium. Microphones are not disparate, so they catch the same thing wherever they are which does eventually not benefit to the surround. TV channels know that they don't hit sound purists or audiophiles or "dB out cutters in 4 parts", but people who bought 16/9 TV set with 'surround sound' inside, thus they are promised a great extra sound. In other words, people want something worth the money they put. It must be "brilliant", with a wide big ambience at the rear that anybody could hear. 90 per cent of people placed rubbish the speakers of their hi-fi stereo, conditions for a convenient stereo listening are rarely gathered. How are they going to place not only two but six speakers ? The multi-channel mix has to be on top, even in the worst conditions. There are physical problems : we do think that there won't be any good surround system until the wires are gone, so that people can put the speakers wherever they want to without needing 4 meters of cables coming out the amplifier. This kind of useful aspect is essential. Bringing the "huge machines" from the American theatre, the DVD is likely to put high standards speaking of sound quality. "For the anecdote, let noticing that some radio stations tried to experiment broadcasting a Dolby surround new program encoded in the two channels of FM radio : for instance France Inter (such as "Le singe soleil", may 97) and RFM (Halloween night or Christmas night). Equipped listeners were enthusiasts... although the analogue herzien transmission must have altered the spatialization a bit !
| Too much ! | |
|
Franck Fradet thus raises a huge problem : until then, the Dolby Digital sound was used to brutalize the ears in American action movies watchers. Fist blows, motors, explosions and any screams : many spectators reported they were bound to leave the theatre, the sound level being too high... It would be too bad that this kind of "aesthetic" be used to prevail and that the DVD becomes synonym of spectacular, of full sound in the ears. Some people think that the flaws of Dolby Digital are hidden by this sound energy blow and are cruelly clarified by classical recordings. So tells Albert Laracine, one of our best sound taker, "at the beginning of the stereo, we could hear some strange recordings, with sounds going from left to right, some nonsense panoramic, as well as sound taking way far from the reality. This phenomena made its way". Perennializing abusive dynamics and spectral used in cinema would reveal too bad speaking about a technology aimed at restoring a sound so precise that it seems to be touchable in the room - as we could notice during the International Forum for Multi-channel Sound at the SATIS. The best proof of that was a recording of a string trio "stereo compliant" which seemed perfect in this format : but once we added the other channels, coming back to stereo was merely impossible. That will be the only condition to the starting of a great surround recordings market. To conclude with the topic, what is 5.1 sound for home studio people ? It is an existing and promising technology which one should not hesitate to discover. More and more digital consoles are going to include surround mixing modes : one has to try, add some reverbs at the rear, premix the ambiences... Furthermore, what about putting some psycho-acoustic spatialization effects in the stereo mix ? There are many pluggin or hardware solutions that many well known sound engineers already use... This will be developed in the second part of the article.!
CD Stereo and Surround CD ?
What happens while playing a stereo CD on a Dolby Surround amplifier ? It is rather simple : everything left or right remains left or right, but thicker. Anything common to both channels will be played by the central speaker. Out of phase elements from the original mix - reverbs and also some sounds - will appear at the rear ! So tells Denis Florent, RFM production executive, a radio station producing programs in Dolby format several times a year : listening to surround disks may bring to nice surprises ! For instance, the last album from Quincy Jones, Juke Joint, recorded with a big band, is astonishing. I'm thinking about a song sung by Ray Charles, Stevie Wonder and Bono with a fabulous sound once decoded. More generally, a single which is widely mixed in stereo will sound good in Dolby while a centred mix, monophonic with reverb on the sides to widens the sound will be badly played in the same conditions. We feel surrounded by sound, with the detriment of the stereo analysis precision. Your servant experiments that everyday on its wonderful Tokai surround amplifier, bought at 990 F (150 euros) at the supermarket, the 5 speakers included...
(sorry, Sir, the sub woofer is optional,really...)
Figures
The Dolby laboratories mainly rely on licences. Thus we won't be surprised that they keep a fine accounting about the technologies they release : 609 patents within 31 countries, 611 brands in 96 countries. Here is the last counting of world wide sells at 21st of january 1999 :
¥ 36 564 000 Dolby Surround decoders
¥ 7 202 000 Dolby Digital systems
¥ 1 873 000 Video DVD players with Dolby Digital (270 types)
¥ 2 075 000 DVD ROM players for computers (118 types)
¥ 1 400 DVD and 500 Laser Discs with Dolby Digital sound tracks
¥ 192 Dolby Surround Video games
¥ 29 DVD-ROM Dolby Digital
From 6 to 8
Six channels are not enough for Sony : 8 channels is better ! Designed for wide screens, the SDDS system (Sony Dynamic Digital Sound) puts not less than 5 speakers behind the screen : left, semi-left, centre, semi-right, right. It is obvious that such a format may bring difficulties to domestic uses, being less presentin the cinema rooms than Dolby Digital or DTS ! Some foresee a great future to the SDDS in the high fidelity systems. Anybody living will see...
Re-use
We owe the basis on the surround sound to a Peter Scheiber. Ray Dolby rented his patent to apply it on movie sound sytem : although he's pretending being the inventor of the system, he still pays royalties to the creator. Another genius creator, Jack Cashin improved the Dolby stereo specifications before creating the Ultra Stereo Labs, the process was first used in the "Nashville" movie from Robert Altman, which was rewarded by an Oscar in 1984. Dolby labs reused the system and use it often. So the company helped to popularize the surround format at the cinema or at the house, but it did not really invented it.
| Reader's opinions | |
|
|
Not registred?
Become a member now! It free and fast and it'd allow you to post news, ads, messages in the forums, change your language/time setting...
|
