I'd hoped to get professional help with the HIDE AND CREEP post-production audio stuff, but it wasn't to be. Of the local audio pros I contacted, they were either out of my price range (big surprise) or too busy working on other projects to help me out. It probably would have helped if I hadn't called these guys at the last minute. So, as much as I'm not looking forward to a crash course in audio-for-film, it looks like I'll be going at it alone for the most part.

Connect

As you might remember from the location audio column, HIDE AND CREEP is a two-system sound project -- the images are captured on film and the audio is captured on a separate machine (our portable DAT recorder).

We had our film transferred to videotape at CineFilm in Atlanta. Like most transfer houses, CineFilm will gladly take the audio from your DAT tapes and synchronize it with the videotapes they make of your film. They also charge money for this service, so I decided to save a few bucks and sync the sound myself.

Getting video footage into my Mac is easy -- it's transferred from the video deck I use to the Mac via a FireWire connection. FireWire is kind of like USB, but faster -- fast enough to copy DV-quality video in real time.

Getting audio from a DAT machine into the Mac, however, is a different story. DAT machines do have a digital output, called S/PDIF, but most computers don't have a built-in S/PDIF input. Luckily, it didn't take me long to find a S/PDIF-to-USB converter made by Edirol. I got it for less than 100 bucks, and it did a fine job of getting the audio from the DAT to the Mac. For folks interested in something a little fancier than the Edirol gizmo, DigiDesign makes the Mbox, which converts all kind of audio signals, S/PDIF included, to USB and costs around $500.

Speed

As I mentioned earlier, film footage runs a little slower after it's transferred to video. Film is usually shot (and projected) at 24 frames per second. Due to our broadcast television standards, film is actually transferred to videotape at approximately 23.98 frames per second. So our HIDE AND CREEP film footage, having been transferred to video for editing, has been slowed down by 1/1000 of a second. The audio is playing back at the same speed it was recorded.

The obvious question here is, "What difference can 1/1000 of a second make?" Usually, not much. In general, our takes on HIDE AND CREEP were pretty short, and if I'd synchronized the raw sound to the video, it wouldn't have been a problem. But for long takes, the audio and video sync would get off by one frame every 50 seconds. So if a take runs for a couple of minutes, sync ends up off by more than 2 frames. Which is really obvious to the viewing audience. I guess you could only speed correct the really long takes, but it's quicker and easier (and better) to resolve all the audio, thanks to the magic of computers.

There's plenty of audio editing software that will allow you to change the speed of a sound file. Sound Forge is one of the more popular ones, but it's not available for the Mac. I ended up going with a shareware program from Felt Tip called Sound Studio. It's not as feature-rich as Sound Forge, but it's great for resolving audio for film transferred to video.

For each audio file that needed to be slowed down, I used Sound Studio's "Adjust Pitch" option to set the pitch to 99.9%. As the name implies, "Adjust Pitch" actually changes the pitch of the audio, which would make everybody's voices sound funny if the adjustment wasn't so minute.

A side effect of adjusting the pitch is that the sample rate of the audio file goes from 48 kHz to 47.952 kHz. But that's no problem, because Sound Studio also features a "Resample" option to get us back to 48 kHz while leaving our audio file's playback speed at 99.9% of what we started with.

I know this probably sounds like a lot of hassle, but it's not so bad after you get used to it. Ideally, Apple would come up with a "Resolve Audio for Film-to-Video" option for Final Cut Pro, where you could import your video and audio, click one button and have the computer figure out the rest. Until that glorious day arrives, I'm pretty happy with the Sound Studio solution.

If you'd like to read a little more about all this audio/video speed-resolving stuff (I know it's exciting), the article that finally set me straight on the matter is at ZeroCut.com.

Sync

Editing on computer makes the actual sync process a breeze -- assuming you used a slate to mark shots during shooting. The slate has a hinged pair of sticks attached that can be clapped together to mark the beginning of each shot visually (you can see the sticks coming together) and audibly (the sticks make a pretty loud "click" sound when they meet).

After your video and audio is in some non-linear editing system, you can just slide the picture and sound around until they're synchronized, based on the slate for each shot.

Even if you don't have a slate for a particular shot, there's often a good sync reference in there somewhere. Any event that you can see clearly and that makes a distinctive sound can help you find sync. Editing HIDE AND CREEP, I found that car doors being shut and rifles being cocked are great substitutes for a slate.

I've also had to occasionally sync sound to picture with no point of reference other than the actor's mouth and dialogue. It's not impossible, but it's not any fun, either. As far as sync methods go, it's the last resort.

Mix

After I got all my audio in the computer and synched to picture, I didn't mess with it much while I was editing. Whether the sound was good or bad, as long as I could hear most of what the actors were saying, I left it alone.

However, when complete scenes started to come together, problems in the audio started to make themselves more apparent. The first thing I fixed was differences in the volume of the audio from shot to shot within a scene. Production audio volume tends to vary from one shot to the next, since it's impossible to keep a boom mic in the exact same position relative to the actors for every take. Final Cut, like most any video editing software, allows you to adjust the volume for each shot. You can even "ride the gain" and adjust the audio levels within a single shot.

Final Cut also features a display window with audio meters, similar to the ones on a DAT machine. As with location audio, it's recommended that you keep your average playback level around -12db. While working on HIDE AND CREEP, I noticed our recorded levels were a little low, making a -12db average unattainable for some of our audio. So I lowered the average levels a bit to -18db.

Basic EQ

When you're watching a big Hollywood movie, the crystal-clear dialogue and sound effects you hear probably didn't start out that way. Pro-audio mixers know how to use EQ (equalization) to get rid of any nasty-sounding frequencies in the mix.

Not being a pro-audio mixer, I didn't try to get too fancy with the EQ. I did use a Final Cut Pro high-pass filter to get rid of frequencies below 200hz for most scenes. The human voice, the most important element of the HIDE AND CREEP production audio, doesn't dip far below 200hz, so cutting these frequencies doesn't terribly alter the tone of the actors' voices. It does, however, cut down on wind noise in outside shots, road noise in car shots and the occasional "bump" picked up by the mic if the boom pole is mishandled. For scenes with lots of low-end racket, I'd go a little farther and cut out everything below 240hz.

Guys who know more about audio than me have said cutting frequencies below 200hz is a bit extreme -- they usually don't recommend cutting anything above 80hz. But I had too many low-end noise problems for 80hz to do much good, so I went with 200hz.

If you're working on your own project in the digital world, feel free to experiment. The great thing about computer editing is that, if you're not happy with your last change, you can always hit "undo."

I think that's enough talk about sound frequencies, sample rates and playback speeds for now. I'll try to wrap up our post audio discussion next time in Part 16: Mix Harder. Or maybe Part 16: Mix With a Vengeance.

In the meantime, since I'm always looking for feedback from you guys, I thought I'd try a contest. Well, more of a lottery, actually. I'm going to give away a DVD-R of HIDE AND CREEP, the very same DVD-R currently going out to film festivals and the press, to a MOVIE POOP SHOOT reader. On top of that, I'll throw in a DVD of a low-budget indie classic -- something like EL MARIACHI or SLACKER or FOLLOWING -- so it'll be a good prize even if HIDE AND CREEP doesn't live up to the hype.

If you'd like to enter, just send me an e-mail with a comment about "This Movie Ain't Gonna Shoot Itself." And be honest. Bad reviews of the column or harsh criticism of my abilities as a writer won't affect your odds of winning -- everyone who gets an e-mail to me before I write the next column is eligible. If you want to make my job a little easier, put something about "Shoot Itself" in the subject of your e-mail.

I hope to hear from you, and I hope you'll stop by next time for more audio adventures.

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