Stereophony and audiovisual post-production

Sound reproduction in movie theaters has improved dramatically in recent years thanks to the generalization of broad-spectrum and multi-channel systems such as Dolby SR, Dolby SR-D and DTS systems. In the same way, the advent of the DVD (Digital Versatile Disc) and its ability to decode multichannel sound such as Dolby Pro Logic, Dolby Digital and DTS bring us closer and closer to a spatialization of sound reality that seeks new sensations in the global perception of the audiovisual show.

Of course, the use of stereo sound cannot be free and must be closely related to the narration and dramaturgy of the project. Cases have been seen of exaggerated stereophonic effects that distract and "derail" the viewer from their concentration in front of the screen (central conical projection).

While it has evolved towards a rationalization in the use of stereo sound, it would be good to reflect on the manufacturing processes of the stereophonic soundtrack.

It may seem strange but when a director is clear about his film project the decision to use stereo in some specific scenes has to be consulted in advance with the Sound Engineer and the Production Director. What does it mean to shoot or not in stereo? After many experiences of shooting in direct sound it has been concluded that stereophony is better to "manufacture" in the mixing auditorium. Shooting with stereophonic microphones means strictly adhering to a technical script where camera movements, axes, sound environments and staging have to keep coherence for the assembly. You can not falsify planes and surely there will be problems of raccord in the spatialization and location of sound sources. The film Detective (1984) by Jean-Luc Godard was written and staged to be shot in stereo, cinemascope and fixed shots. A stereo microphone following a camera panorama produces an exaggerated displacement of the sound backgrounds (dizziness effect) and surely unjustified at the time of assembly. In addition, recording dialogues with stereo microphones, for example MS, is compromising too much the understanding of the dialogues due to the use of a cardiode microphone to collect the M information. This, coupled with wide camera framing and ambient noise, can cause more problems compared to what it would bring to the stereophonic record of a situation.

Obviously, the quality and richness of the sound environments and acoustics of certain locations recorded in stereo are irreconstitutable in post-production. The most frequently used method is to roll the dialogues in mono or "bipista", that is, several microphones mixed in monophony or make the recording of the reed and the wireless (HF) separately in two tracks (left channel = reed, right channel=HF). Raccord environments and supplemental sounds can be recorded in stereo after the scene is over. The microphone used, in general, is an MS that is, in theory, Mono compatible. AB phase stereophony can present problems for encoding in the Dolby A and SR system. With the new digital systems (SR-D and DTS) this problem would not arise, but some experiences carried out in France showed that the MS can produce more catastrophic effects than the XY or AB stereophony.

The sound environments in MS are recorded without encoding and in bipist (left channel = M, right channel = S) leaving the encoding for the moment of mixing. The great advantage of the MS with respect to the other types (XY, AB) is to allow opening or closing the stereo base to the taste of the mixer and depending on the correspondence with the projected image.

The recent use of four-channel digital recorders allows a great flexibility of the sound recording. For example, record dialogues and environments at the same time: CH1=Cane; CH2=HF; CH3=M; CH4=S; 1 rod and 3 separate HF, or use several multitrack recorders and many wireless in the best Robert Altman style.

One of the stages of sound post-production that has been most favored with new digital technologies is precisely the sound assembly. If we go back a little in time, the assembly in moviola and magnetic perforation 35 mm allowed a limited number of soundtracks to be heard simultaneously. Each band is composed of 3 tracks formed as follows: 1 = mix cane + HF; 2=cane; 3=HF. Only in the final mix and after having made the premixes of dialogues, environments and music could you have a global idea of the sound assembled. In addition, stereophony requests twice as many tracks for environments and music.

It is there that the non-linear assembly proposes an almost unlimited number of tracks and becomes an excellent tool for some and at the same time a "headache" for others. The simplicity and effectiveness of the soundtracks of the 60s contrast in most cases with the current, crowded and meaningless ones. It all sounds, but who said that everything that sounds is interesting to the story?

In the current sound montage and in stereo we can easily find 60 tracks for the assembly of environments of an action scene. Of course, it is better that there are too many sounds and not that they are missing. Anyway you can eliminate the undesirables in the premixes and it does not hurt to have different proposals to present to the director.

Stereo sound assembly requires a specific technological environment. On the one hand, the readers from which we will take the sounds (1/4 ", DAT, CD, Optical Discs) and the non-linear system based on hard drives (ProTools, Sonic Solutions, AKAY DD 1500 and others). On the other hand, a quality monitoring system and in accordance with the standards of multichannel stereophony, either Dolby SR (4 channels), 5.1: DTS and Dolby Digital (6 channels) or SDDS (8 channels).

Sound monitoring based on a stereophonic simulation that will be used in the room, helps a lot to reflect on the spatialization and location of point and environmental sound sources.

In the same order of ideas, the use in the assembly of the virtual console or one or more automated consoles (ex: 2 Yamaha O2R in cascade) allows to elaborate pre-mixes that as a model give us an idea of the relevance of certain sounds in correlation with others and of these with the dialogues.

This process would ideally be completed with a video projection, at least on a medium screen, with the help of a good video projector.

Non-linear systems also offer us the possibility previously dreamed of quickly moving a track, bending it, filtering it and in general, processing it with great ease thus creating a universe of sound treatment possibilities.

Gone are the days when mixing was done precariously on video (2 or 3 tracks) or even in cinema with magnetic punch readers. With systems based on hard drives we can have access to all the tracks in real time, mix and even rearrange at the last minute the mounted sounds without altering the rest of the assembly.

There are two mixing techniques in the world. In the U.S.A. 3 mixers cohabit in the same room in front of a large console divided into 3 parts. In the center is located the mixer of the dialogues and on the sides, the mixer of the environments and the music. They all participate at the same time but are coordinated by the dialogue mixer, which confirms once again the eternal subordination of the environments and music to its older sister: the word. The intelligibility and understanding of what is spoken demands it.

The European and Latin American style (yes there is one) involves the realization of the pre-mixes of dialogues, environments and music by a single mixer. This process requires several weeks, on average 4 for a feature film and the participation of a single person working in direct coordination with the sound editor. It is a less divided work than in the U.S.A. In addition to the image editor, the sound will necessarily be in the mix (at least in France).

It is in the mixture where the exploitation of stereophony as a narrative, realistic or abstract resource is finally decided: scene in a room without external visual reference but recreation of the exterior environments by stereo; use of suround (later environmental) channels to convey "out of frame" effects; or simply magnificent exteriors of people or landscapes supported by stereophonic environments typical of the place.

There is a great technical challenge in terms of the correct restitution of stereophony in the room. The conditions of maintenance and calibration of the mixing rooms must be strictly adhered to, as well as ensuring the supervision of the process by a competent technical team (e.g. Dolby Consultant), and of course, the same for the cinemas. As everything cannot be rosy, the viewer should sit in the "ideal chair", that is, in the midline of the room (optical projection axis) and 15 meters from the screen (85 dB SPL). That is the place where the mixer sits, and the point where the sound level and spatialization are decided.

The ear of the spectators becomes more demanding because of the permanent exposure to better projection conditions in cinema and even in the T.V. From the stereo HI-FI VHS to the DVD, passing through the conditions of restitution of a Home Theater system, we could say that the overall quality of sound reproduction has reached very high levels. This requires a constant concern for the way we must ensure a sound record of incontestable technical quality, without forgetting that technique is not everything.

Stereophony somehow destroys the active character of monophonic perception. Imagining where the sounds come from, from the left or the right, makes the viewer participate more actively in the reconstruction of their own sound spaces, imagining them permanently. Stereophonic spatialization establishes a unique representation of sound space, siren on the left, children on the right, cars passing from left to right... Few things are left to participate imagining, it looks a bit like the world of radio.

A sound without soul and meaning will not go "unnoticed", in the unconscious sense of the term. On the contrary, it will be noticed by alerting the viewer for its lack of relevance to the narrative.