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Lesson 2. About Digital Video Editing > Using audio in a video

Using audio in a video

Audio can play an equally important role to imagery in telling your story. In Adobe Premiere 6.5, you can adjust audio qualities in the Timeline window, or use the Audio Mixer with greater flexibility and control when mixing multiple audio tracks. For example, you might combine dialogue clips with ambient background sounds and a musical soundtrack. Mixing audio in Premiere can include any combination of the following tasks:

  • Fading, (increasing or decreasing) the volume levels of audio clips over time.

  • Panning/balancing monophonic audio clips between the left and right stereo channels. For example, you may want to pan a dialogue clip to match a person's position in the video frame.

  • Using audio effects to remove noise, enhance frequency response and dynamic range, sweeten the sound, or create interesting audio distortions such as reverb.

When you import a video clip that contains audio, the audio track is linked to its video track by default so that they move together. Adobe Premiere 6.5 allows you to adjust and mix audio while you watch the corresponding video in Real-Time. The Audio Mixer window, like an audio mixing console in a professional sound studio, contains a set of controls for each audio track; each set is numbered to match its corresponding audio track in the Timeline. When you edit superimposed video tracks, remember to consider the effects of your edits on the audio tracks.

For more information, see Chapter 5, “Mixing Audio,” in the Adobe Premiere 6.0 User Guide.

Understanding digital audio

You hear sounds because your ear recognizes the variations in air pressure that create sound. Analog audio reproduces sound variations by creating or reading variations in an electrical signal. Digital audio reproduces sound by sampling the sound pressure or signal level at a specified rate and converting that to a number.

The quality of digital audio depends on the sample rate and bit depth. The sample rate is how often the audio level is digitized. A 44.1 kHz sample rate is audio-CD-quality, while CD-ROM or Internet audio often uses a sample rate of 22 kHz or below. The bit depth is the range of numbers used to describe an audio sample; 16 bits is audio-CD-quality. Lower bit depths and sample rates are not suitable for high-fidelity audio, but may be acceptable (though noisy) for dialogue. The file size of an audio clip increases or decreases as you increase or decrease the sample rate or bit depth.


DV camcorders support only 32 or 48 kHz audio; not 44.1 kHz. So, when capturing or working with DV source material, be sure to set the audio for 32 or 48 kHz.

Keeping audio in sync with video

Be mindful of audio sample rates in relation to the timebase and frame rate of your project. The most common mistake is to create a movie at 30 fps with audio at 44.1 kHz, and then play back the movie at 29.97 fps (for NTSC video). The result is a slight slowdown in the video, while the audio (depending on your hardware) may still be playing at the correct rate and therefore will seem to get ahead of the video. The difference between 30 and 29.97 results in a synchronization discrepancy that appears at a rate of 1 frame per 1000 frames, or 1 frame per 33.3 seconds (just under 2 frames per minute). If you notice audio and video drifting apart at about this rate, check for a project frame rate that doesn't match the timebase.

A similar problem can occur when editing motion-picture film after transferring it to video. Film audio is often recorded on a digital audio tape (DAT) recorder at 48 kHz synchronized with a film camera running at 24 fps. When the film is transferred to 30 fps video, the difference in the video frame rate will cause the audio to run ahead of the video unless you slow the DAT playback by 0.1% when transferring to the computer. Using your computer to convert the sample rate after the original recording doesn't help with this problem. The best solution is to record the original audio using a DAT deck that can record 0.1% faster (48.048 kHz) when synchronized with the film camera.

Older CD-ROM titles sometimes used an audio sample rate of 22.254 kHz; today, a rate of 22.250 kHz is more common. If you notice audio drifting at a rate accounted for by the difference between these two sample rates (1 frame every 3.3 seconds), you may be mixing new and old audio clips recorded at the two different sample rates.


You can use Adobe Premiere 6.5 or a third-party application to resample the audio. If you use Premiere, be sure to turn on Enhanced Rate Conversion in Project Settings > Audio. Then, build a preview of the audio by applying an audio effect with null settings.

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