For a video producer, so much time and attention can be paid to the camera, lighting, subject, and background — the mise-en-scène, if you will. Audio can often be an afterthought, but bad audio has the ability to sink your project like a lead balloon. The most commonly bungled discipline for film students and novice filmmakers alike is audio recording and mixing, and it’s an aspect that tends to be more objective than the visuals. If the audio is bad, everyone knows it.
So, for any production involving multiple microphones and subjects, it’s best to have an audio recordist and mixer on set. And once you’ve captured your audio, it’s important to process it correctly in post-production. Below are some basic techniques for mixing audio for your video project. For my own projects, I usually use only one or two mics, creating four to six layers of audio which are split into dual mono. These techniques constitute the bare minimum that you should be doing with your own audio in post-production. I’m using Premiere Pro CC in the examples, but these techniques can be applied in all the commonly used video-editing programs.
Once you’ve imported your audio clips into your project, take a look at where they’re peaking. Nothing should pass or even approach zero; going above zero will result in distorted audio. All sound levels should stay in a range of about -24 to -6. Often, dialogue sits between -18 and -9. First listen to your A-roll audio — your interviews and on-camera dialogue,with the footage that drives your narrative — and start by adjusting the gain. This can be done in either your project panel or directly in your timeline. I prefer to do it in my timeline, adjusting just the pieces of the dialogue I know that I want in my cut. Once these A-roll tracks are set, adjust all the other audio track levels to match them. Both gain and volume refer to the loudness of the audio; however, gain is the input level of the clips, and volume is the output. But remember, increasing the gain will also increase the noise.
Once your primary audio is adjusted using gain, you’ll want to move on to your secondary audio, which is often your music. Again, preview your track and adjust the gain accordingly. Insert your music into your timeline and listen, then work with the levels by inserting keyframes. You can figure out the levels by adjusting the clip keyframes, or adjust keyframes on the entire track — whichever makes the most sense for your clip lengths. (I tend to avoid track keyframes and just work within the audio clips.)
When filming, you’ll often pick up some room tone or background noise in addition to your A-roll audio. Maybe the air-conditioner or refrigerator kicked on and off during your interviews and there’s inconsistency in the ambient sound. Hopefully you’ve recorded some room tone on location that you can use to lay under your audio to keep the sound consistent. You can then copy and paste “band-aids” of room tone in places where it should exist and doesn’t. You probably only need to do this if you don’t have a music bed underneath the dialogue that would dampen or entirely cover the room tone.
You’ll sometimes need to go through the process of de-noising, as well, which will remove ambient buzz or hum recorded during production, or noise introduced when increasing gain in post. Apply the “de-noiser” audio effect to your clips and adjust the reduction slider as necessary. If you slide too far, you can distort the tone of voice, so be sure to find that middle ground in which the background noise is removed but the original sound of the speaking voice is preserved.
Pretty much every audio clip in your timeline should have a crossfade on either end. These crossfades are usually only a few frames and cover subtle pops that occur when audio clips cut in or out; sometimes they just ease the transition from one clip to another when “franken-biting” multiple sound soundbites together. Longer crossfades are more common in music tracks, especially when turning corners within the piece or at the beginning or end of a piece.
Finally, pan your mono audio channels. I prefer to track my audio as dual mono and individually pan the tracks as the action in the video dictates. This gives me creative freedom in customizing the sound of my video. As action moves from one direction to another, I can track it sonically by panning the audio track in that same direction. This process can have significant psychological effects on an audience. Try it yourself — play a clip with action moving across the frame and listen to it with balanced audio channels, then again with audio panning in the direction of the movement on screen. It feels much more natural and your eyes will tend to move not only in the direction of the action, but also in the direction of the audio pan.
Do you have any go-to audio-mixing techniques for video of your own? Share them in the comments below!