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The Art And Technology Of Listening, Part 3
Transferring, editing and mixing audio
By Carmen Borgia

Now that youíve recorded it, what shall you do with it? The recording of the sound and picture on set is the production phase, now weíre in postproduction.

  1. Transfer
    Youíll be working in an editing system and must get the audio media into it. If youíve recorded onto a device with a hard drive or flash card, youíre close to home. As long as you keep the file format, speed and resolution of the audio the same as the original recording, you can copy onto any digital media with impunity -- CD, DVD, firewire drive, SCSI drive, flash card, jump drive, ipod, FTP, email and your laptop, all different containers for the stuff youíve digitized. It is good practice to confirm some parameters of your copies to make sure you are copying the data correctly. Check things as file size and file format to make sure the copy matches the source. Itís never a bad idea to actually open up the copied file and listen for that bit of certainty that life so rarely offers.

    If you recorded to tape, youíll have to transfer the audio into the system in real time. From DV, you will load audio into your system via firewire. This digital transfer in theory should make a perfect copy of the audio. Even digital-to-digital copies can be corrupted with clocking errors and other noise. Listen to the result of the transfer for distortion, change in level, little tiny clicks or pops and summing of tracks from stereo into mono. The DV will start with two tracks, and there should be two tracks once itís in your system.

    Copying audio from CDís usually entails a sample rate conversion, since you will likely be editing at 48khz and CDís are 44.1khz. Be sure to actually copy the files as converted 48khz audio. If you donít, your system must convert the sample rate on the fly. This is bad because it makes your system work harder and may contribute to overall performance problems. More maddening is that mixed sample rates can trip up your OMF export later, so keep your audio consistent within your system.

    If youíre coming from DAT, 1/4Ē, cassette or minidisc, youíll be getting in via analog. Use a system with best quality audio converters, and listen carefully to the transferred audio over good speakers to be sure it all worked. Real time transfers are subject to many little issues that may alter the audio, and you always want the audio to be as close to identical to the original as possible.

  2. Editing
    You can do a perfectly acceptable sound edit on your picture editing system, even one that is of the lower budgetary kind. The most time-consuming aspects of editing are finding the right audio and arranging it on tracks in an orderly manner. So long as you acquire the audio as a digital file, such as copying from a CD or via firewire, the sound quality will be identical to a more expensive system. If you are coming in analog, such as through a microphone and preamp, you will want to be sure that the converter hardware into which these are plugged be of high quality. Working in Pro Tools or some other editing system can be a great way to go because an experienced operator can work more quickly in a system optimized for sound editing. In any case, youíll have to work with the audio to some extent while doing the picture edit just to make sure the current cut of the film is functioning, artistically. The following editing tips apply to all systems.

    The edit is where you choose the audio you will use in your final product. If your film is using only the audio recorded on location, such as a documentary, you will edit the existing audio so that it can be mixed into a smooth whole. One would think this would be the easiest kind of edit, as there tend to be fewer tracks with less added ambiences and effects. In truth, these are difficult because there is no place to hide. This is because of masking.
    Masking is a psychoacoustic effect where one sound hides another, and it is the bedrock of audio editing for film. It is only natural when you record your sound on location that audio from one shot may not necessarily match that of the next shot. This is due to unavoidable variations in microphone placement relative to the room where you place it and relative to the subject, you are recording. When the audio of adjacent shots does not match, you must smooth it out. You can do this in two ways.

    Ease the transitions with audio dissolves. If the background sound (room tone) abruptly shifts from one shot to another, the shots must overlap and dissolves added between them. These soft transitions fool the ear into thinking that the reality between the two previously unrelated shots is continuous in the reality of the film. How much transition do you need? It depends upon how different the adjacent shots are. The bigger the contrast between shots, the longer the required transition. If audio between shots is identical, you may need no transition at all and a hard cut between shots will be acceptable. Slightly contrasting shots may need a half-second or less. Severely contrasting shots may require a couple of seconds of dissolve between them. You will be limited by the amount of available overlap in your takes. If a subject speaks non-stop, with no gaps between words, you may have to build out room tone to have sufficient overlap.

    Add room tone. If your audio takes have wide variations in background noise, you must add some of the noisy room tone in a separate track under the quiet (well recorded) takes to help even it out. The implication is clear: the overall room tone of a scene cannot be lower than that of the noisiest take. A scene that can be spread over two tracks will thus end up with at least a third track of tone that will make it play consistently.

    Consistency is more important to how sound in a film plays than overall noise level. If an audience hears jumps in noise level between shots they will be taken out of the film without quite knowing why.

    If a scene is too noisy, you may wish to re-record the dialogue for that scene, also called ADR (automatic dialogue replacement), looping or dubbing. This is a complex undertaking, involving scheduling the actors into a studio, causing them to re-read their lines with the appropriate energy and interpretation, adding ambience to match the original production sound and adding foleys of any sounds the actors may have made while doing the original scene, such as walking or shifting about in their chairs. The director must work with the actors and the sound engineer must coax them to make it work. It doesnít sound like the original and people become cranky. In the case of a documentary, there are probably no actors, just subjects who may not be available, willing or even capable of performing such a task. Replacing dialogue is hard, so it is best to consult a professional.

    Music editing. In films with tight budgets, music is usually added while the picture is being edited. Music is either taken from CDís (with the appropriate permissions) or composed on a separate system and dropped in as mixed sound files. The music cues are placed to work with the picture; various music cues may be tried before finding the one that works best. Cues may be chopped up, re-arranged, truncated and duplicated once they are on the tracks to make them shorter or longer or to generally fit the picture better. Music has its own set of rules, and having a person with musical chops involved in the edit insures that the music retains its feel. Audiences will sense changes in music even when it is playing under dialogue, so try to keep your tempos, rhythms and progressions in the pocket.

    Effects editing. You may enhance the feel of a film by adding sound effects to it. Hard effects, the kinds that sync up with images on the screen can add detail, realism and impact to a scene in addition to helping to draw focus to specific events in the frame. If money is changing hands at the bottom of the frame, a little paper crinkle at the right moment will call attention to the action. Background ambiences that run under entire scenes will make them play more easily on the ear if not overdone.

    Effects come from production sound, effect libraries, Foley work and postproduction field recording. For those regularly engaged in post production, it is essential to have at least one good sound effects library; thirty or forty well-indexed CDís will last you a long time. They cost more than regular CDís because legal rights are included in the price of purchase. One would think that effects from such a library would be easily overused, but because these effects come layered with existing production sound they have a longer life than their visual clip art counterparts do.

    OMF exports. If you have to move your edited audio from one system to another, youíll be doing an OMF export wherein you convert the various tracks, regions and audio media into a lump of data that can be opened in Pro Tools or other mixing system. This operation should be coordinated with whoever is doing your mix. If you mix within your editing system, you will not need an OMF.

  3. Mixing
    Once all of the audio has been selected and placed in the sound edit, it is mixed. Filtering and equalization is added as well as reverb and other effects. The balance between the various elements is decided, and the overall absolute volume is set. If your distributor has requirements for the elements, the mixer makes sure that the final audio conforms to the specifications. If you do one audio operation at a post house, it should be the mix.
    Equivalent to a video online session, the mix is where you put the finish on the sound for your film. The mix room must have a high quality mixing system. The room must be quiet and comfortable for the hours of work that is required for long-format projects. The speakers must be of high quality, and the acoustics of the room must be neutral. The picture must be viewed at a good resolution on a system that holds sync, does not drop frames as some inexpensive firewire DV converters do and does not introduce a delay in picture playback as some plasma displays do.

    Cost effective picture editing systems tend to have a handy toolbox of audio gizmos to clean up your sound. Audio in these cases tends to be an afterthought to the primary function of the systems, which is to edit video. A dedicated mix room with an experienced mix engineer will be an improvement on a picture edit mix every time. If you choose to mix in your picture system, at the very least, you should set up your room for audio, and all of the above requirements apply.
    To mix you will need an OMF export and a picture reference tape. The OMF has all of the sound that has been prepared in your picture system. The picture that you must mix to is the reference tape. The most efficient workflow is to lock your picture prior to mixing which will save you the labor of having to recut the audio in your mixing system to match updated image edits. You should take care with the reference tape to insure that it is an accurate output from your system, with no dropped frames or other mayhem. It should have a reference mix on the audio tracks of the tape. The tape must have a 2 pop at the head and again at the tail of the program; the OMF must have a beep to correspond to each 2 pop in the picture. Armed with a good reference tape and an OMF, you can trust the sync of the sound with the picture and you will be able to make any final sync adjustments to the audio during the mix.

    If youíre new at this and decide to mix the project yourself, check the mix on a variety of playback systems to insure consistency of intelligibility, sync, balance, loudness and overall tone. The world of consumer audio is a treacherous and chaotic landscape for homo sonus, and a mix will not play back the same on any two systems. The goal is to craft a mix that holds up well on the greatest number of systems. People who mix sound regularly have many opportunities to hear their finished work over the life of a given film which helps them make good decisions while doing the mixing.

    To maximize your odds and accumulate some of your own knowledge, listen to the mix very quietly. Play it in the living room and listen from the kitchen. Listen over big speakers. Listen over small speakers. Play it over your TV and compare it to ten of your favorite DVDís of various genres. Screen your mix for some viewers who are unfamiliar with the film and do a little survey. Could they understand all of the dialogue? Did the film lose them at any point? These sorts of inquiries will help you gain valuable insight into how well the sound is functioning in your film and sharpen your ears besides.

To Summarize:

  1. Transfer the audio from your location sound device into your editing system as accurately as possible.

  2. Assemble all of the sound for your film in one place. This is your sound edit. It includes arranging the dialogue for the mix as well as adding effects and music.

  3. Mix the edited sound to create the final product. Apply equalization and other effects and set the absolute level of the program.

  4. If youíre mixing it yourself, listen to the mix on a variety of systems for greatest consistency of playback.

Our next installment will cover final audio formats and output of your finished mix.


Carmen Borgia is the head of audio services for DuArt Film & Video in New York City. He oversees a post production sound department that provides mixing, sound design, restoration, transfer and printmastering. His department caters to independent projects in all formats from mono optical up to digital 5.1.

Editorís note: If anyone has any questions, please submit them to cborgia@duart.com. Carmen will do his best to answer any of your queries.


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