Scratch Tracks and Why They Matter
A scratch track is an audio recording that provides information on timing and content with the intention of being used as a reference for the final (or replacement) audio. Scratch tracks are used in both music and film.
In film, especially when shooting on location, there are often conditions which make it impossible to record audio of sufficient quality to be used in the final audio track. These include shooting next to a freeway or airport, or other situations where the ambient sound makes quality voice recording difficult or impossible. A classic example would be the film Waterworld, which was shot in an artificial seawater enclosure off the coast of Hawaii. The ambient sounds of the generators and ocean noise required almost all of the dialogue in the film to be replaced with ADR. While the film is generally considered a flop, it was nominated for a Best Sound Oscar.
For situations like this, a scratch track is essential. It may not be great audio, but it captures what was said, the tone in which the dialogue was delivered and the pace in which it was delivered. This allows the actor to recreate (and often improve) their delivery when it comes to re-recording the dialogue in a recording studio using ADR techniques. Without access to a scratch track, ADR is a nightmare.
Animated films also use scratch vocal tracks to set the timing when creating animatics (storyboards that are animated with key frames). The animatic serves as the basis for final animation at which time, professional (and often big name actors) are used to record the final voice track for the animated film.
In music, a scratch vocal track is often laid down by the performer. Once the scratch vocal track is laid down, the music producer and audio engineer use it as a reference to create the musical portions of the song. Usually, the artist re-records the vocal once all the musical elements are in place.
Scratch tracks in music are not limited to vocals—they are often used to record initial guitar tracks, drum tracks and keyboard tracks. One of the unintended, but sometimes beneficial, consequences of laying down scratch tracks is they are often spontaneous and because there’s no pressure on the artist to be “perfect” because it’s only a scratch track, this spontaneity can end up being more alive and passionate than attempts to re-record it. Rupert Holmes’ “The Pina Colada Song,” is an example of song where the scratch track ended up being used.
Often, a musician will lay down a scratch track as they work on composing a song. It might be just them performing on guitar and singing the vocal. This rough “outline” of the song is then used in the studio, with the other band members joining in, using the scratch track as a reference.
The most important thing to remember when recording a scratch track is that while its stated purpose is to just act as a reference, it might actually capture the best performance of the artist. Therefore, the audio engineer must be both casual and thorough. The idea is to make sure that all the microphones are setup correctly, without it taking a long time, so that “rehearsal” mode is still in effect while the “practice session” is recorded. This sometimes leads to a magical performance which is why the audio engineer should ensure that the scratch track is recorded well.