An audio map can help you isolate blips.
An audio blip–usually a short pop, crackle or other disturbance in the normal flow of the audio track–can be the result of many factors, including a file conversion error, a player error, or even a physical disturbance to the recording device. In some cases, you may be able to adjust the audio in an audio editor to eliminate these blips, but in other cases you will need to take the more drastic measure of deleting the blips and covering with filler audio.
1. Launch the video-editing program.
2. Import the video file into the program by choosing “Import” from the File menu. Depending on the size of the file, this may take a few seconds to several minutes. When the import is done, the video clip should appear in the Media Library.
3. Drag the video clip in the Media Library into the Timeline. The video should drop into the video track, and the audio should drop into the audio track of the timeline. Most editing programs, even free ones like iMovie and Windows Movie Maker, separate audio and video so that you can do audio editing.
4. Cut the clip using the razor tool so that you can deal exclusively with the trouble sections. Make the cuts a few seconds before and a few seconds after each blip.
5. Highlight the trouble clips and export to an audio-editing program from the File menu, or highlight the clips and use the audio editor within the video-editing program. Some advanced video-editing software, like Adobe Premiere or Final Cut Pro, have audio editors that you can use to eliminate blips. If the program that you are using doesn’t allow you to see a waveform, which is a “map” showing the peaks and valleys representing volume variations, you should use a separate audio-editing program. You can download free trials of many audio editors.
6. View the trouble clip in waveform. Waveform allows you to see the exact moment on the timeline where the blip begins and ends. It will usually appear as a large peak.
7. Highlight the blip and apply audio filters. You might try turning down the treble or applying a “noise reduction” filter. Experiment and listen.
8. Delete the blip if no audio filter works.
9. Add filler sound over deleted blips. When audio drops out altogether, it is very noticeable. Audio editors use filler sound, or “room tone,” to cover the gaps. Basically, take a few seconds of quiet from another part of the audio and place it in the space left by the deleted blip. You can put crossfades on either side of the room tone to make the transition more natural.