Audio in AE
After Effects is primarily a graphical program; while you can include audio in your compositions, AE gives you only the most basic tools for manipulating it once it's there. I find it's better to do your audio work in a dedicated audio program, create your video and effects in AE, then combine the two in an editing program like Final Cut or Premier. However, occasionaly you may want to have an audio track in AE as a reference, or maybe you just want to add some music to your final project. Here's how...
Importing Audio files
Audio files are brought into AE just like any other footage element - you can either use the import menu command, or just drag the files into your project window. AE supports any file type which Quicktime can read, which means it will work with most audio files you are likely to encounter. I've found it has preview inconsistencies with compressed formats such as mp3 though, so I would generally recomend using either AIFF or WAV formats as both are uncompressed. You can use any common bit depth and/or sample rate, but generally I use 44khz/16bit becuase that is cd quality. If you plan to import your video into an editing program and use it with DV footage you might want to start with 48khz/16bit as that is the standard for DV.
Once your file is into the project window it's like any other file - if you select it a small preview will come up at the top of the window showing you the file format, sample rate, bit depth, etc. You can now add your audio to any composition by just dragging it from the project window into your comp window.
The main difference between audio files and other types of footage, once they're in your composition, is that they do not show up in the comp window - only in the timeline. Your audio file has a duration bar, like any other layer, and you can move it in the timeline to adjust where the audio will begin playing. If you drag the ends of the duration bar in you can trim the beginning and end of the audio file.
You can have as many audio files in a composition as you like. Where they overlap the will be mixed together in your final rendered movie.
Audio has only two properties - Waveform and volume or 'audio levels' - the keyboard shortcut for both is "L". Audio level is measured in decibles and has a range from -48dB (no sound) to +12dB(very loud) with a defalt value of +0dB. You can keyframe the levels property just like any other property. Waveform has a toggle arrow which, when flipped down, will show you a visual representation of the audio waveform. You cannot keyframe or change the waveform directly, but it will change to reflect changes you've made to the levels. Waveform is primarily a reference - for instance, in a song with a clear drumbeat you could use the waveform to show you visually where the downbeats are and then align elements in your composition so they move on the beat.
Normally if you want to do a quick preview of your composition you can just hit the space bar and it will begin playing. However, when you do this AE isn't playing your composition in real time, it's just playing it as fast as it can render it. This means it can't preview the audio because audio needs to move at a single constant speed. To hear your audio you need to do two things. First, check the menu Composition > Preview > Audio and make sure there is a check mark next to the word audio. If there isn't, select audio from the menu and it will be checked. Now preview using either the 0 key from your numeric keypad or shift-0. Both of these will do a RAM preview where the video is rendered first, the audio is mixed, then the whole thing is put into memory and played in real time. 0 plays every frame, shift-0 skips every other frame to conserve memory and speed up the preview. If you still don't hear the audio, check your system volume to make sure the sound is turned up on the computer.
Audio Effects AE has a limited selection of audio effects - a few equalizers, a backwards filter, and some simple delay effects. These are all in the Effects menu in the Audio sub menu. You apply them just like you apply a filter to any other layer, and you can set their properties in either the timeline or the effects window. These effects can also be keyframed like any other effect.
Rendering with Audio
Prepare your comp to render just like you normally would. When you click on the Output Module to change your compression settings, before you click on format options look at the bottom of the Output Module window - there is a section for audio. Normally the section is grayed out, but if you click the checkbox next to it you will turn on audio output for your render and the various settings will become available to you. There are three drop down menus for sample rate, bit rate and stereo/mono - the default settings are for CD quality audio and are generally good for anything you'll do.
There is also a "Format Options" button just like the video section has, and it's primary use is the same - you can choose a compression format for your audio, which will save file space in the rendered file. I'd recommend using QDesign Music2 for most of your work. Once you have selected the codec from the drop down menu you can also click on the Option button to set a data rate - for QDesign I'd recommend using the highest data rate of 48kbits/second.
Once you've set your output module to include audio you can render your project. The finished video should have all of your audio mixed into it.
That's it for audio in AE...it's pretty basic, and for anything more elaborate than a music track or some simple sound effects I'd recommend mixing your audio after you've rendered in another program dedicated to audio.