Only two audio-only file formats are supported for editing within Final Cut Pro. Supported Audio formats include WAVE and AIFF files. To use a different file format, you must convert the original format, such as MP3 files, to a compatible format using the Pro version of the QuickTime Player (which is bundled with FCP 4 for free) or another audio application such as Pro Tools or even iTunes. You can even import a file, then export it as a supported file format from within Final Cut Pro choosing File/QuickTime Conversion, and selecting aiff and 48kHz as its file format. Then you import that file into Final Cut Pro for editing. Using compression is not a good idea. In fact, compressed audio files don't work with Final Cut Pro. Audio files are relatively small compared to the file size of video and graphics files in general. The higher the quality you preserve, the better the sound will be. Final Cut Pro converts these compressed files anyway, so just avoid using them.
The AIFF and WAV formats can be sampled at different rates. Sampling is the process used when you convert analog sound (like that which is created by a microphone) to digital audio files. The higher the sampling rate, the more samples that are taken, and thus the better the fidelity or sound reproduction of the audio files.
The different sampling rates are expressed as kHz settings. The higher the number, the better the sound. The most common rates of source files you will encounter editing with Final Cut Pro are 32kHz, 41.1kHz, and 48kHz. DV audio can be recorded as 12-bit or 32kHz (which contains four tracks of audio) and 16-bit audio. These bit depths represent the amount of information recorded in each sample. 12-bit recorded audio should be captured at 32kHz 16-bit, and 16-bit recorded DV audio should be captured at 48kHz 16-bit. Most CD audio files are sampled at 41.1kHz. So sound effect libraries and music CDs have this sampling rate and are always 16-bit recordings.
Some sets of audio sampling rates are lower than 32kHz; they range from 8 to 22.225kHz. They are strictly for use in multimedia projects. You should avoid them for editing within Final Cut Pro, because they aren't of a quality you want to work with. You can't improve their sound quality, and you want to edit in as high a quality as you can as long as you can, even if your final output destination is one of these formats.
The files you imported for use with "The Midnight Sun" that were recorded specifically for the movie were recorded in two ways. The sound sync (on-camera dialog) was recorded to a DAT while the film was shot. Then it was converted to AIFF format. The rest of the voice-over (the actor's read of the poetry) and foley (sound effects recorded in sync while the performers watched playback of the picture) were recorded in an audio studio and were saved as AIFF files. The rest of the files you imported were from sound-effects libraries and music CD libraries. These original files were also saved in the AIFF format. All the files have the same sample rate: 44.1kHz, the native format they were recorded in.
When mixing sampling rates within a project, it's best to up-sample rather than down-sample. If you mix 44.1kHz sampled audio, it will play better if you convert it to 48kHz to match the better rate recorded in the DV's audio. The reason is that you are asking your computer to up-convert these files in real time to the sampling rate you've set your DV Timeline to, for example. Faster Macintoshes (such as G4 dual-processor machines and the new G5 machines) up-sample these mixed formats in real time, but the demands on your computer are higher. This up-sampling might lower the number of real-time audio tracks that play back reliably. If you are working with many audio tracks (as you will while editing this tutorial), it's best to match sampling rates within your project with the sequence settings so that all the computer's processing power is used to play back your sequence and is not diverted to up-conversions.
If you mix 32kHz DV audio with 48kHz audio in the same sequence, you might experience popping sounds or other distortion. I highly recommend that you not record 12-bit audio DV in the first place. Mixing these two rates is problematic . 16-bit recordings have more information per sample and thus result in higher-quality audio. This is not quite as important in Final Cut Pro 4, because the quality of the resampling rates depends on the setting specified in User Preferences. Nevertheless, it's a good idea to match those settings by up-sampling them all to the same rates.
FCP 4 introduces clip-level rendering, which helps alleviate this problem. After you resample at the clip level, this resampled file moves with the clip and is rendered at the highest quality, saving repeated rendering of audio and giving the highest quality without losing tracks of real-time mixing. We'll discuss rendering in more depth in Chapter 11, "Video Filter Effects and Basic Compositing."
If you're having audio such as voice-overs, automatic dialog replacement (ADR), or sound effects and original music recorded at a professional recording facility, you can often request that your source material be formatted as digital files and placed on CD instead of on tape. (This method was used in the development of this book, although the audio was mixed originally at the recording studio and was married to the picture there.) This way, you don't have to capture audio in Final Cut Pro from tape. You can just copy the audio files to your hard disk drive and then import them into Final Cut Pro. You don't want to import files directly from the CD. Instead, copy them to your scratch disk and import them from there into the Browser. Playback is more reliable from disk drives than from your computer's CD drive, and when you eject the CD, the files will be offline if they are connected to the CD and not locally stored on your scratch disk.