When filming a video, it’s common to record sound using more than one device. A camera might capture basic audio through its built-in microphone while a separate recorder captures higher-quality sound through a dedicated microphone.

The camera’s audio might not sound particularly impressive, but it can still be extremely useful during editing. This temporary reference recording is known as scratch audio, and it plays an important role in many professional and independent video production workflows.

What Is Scratch Audio?

Scratch audio is a reference recording captured during filming, often using a camera’s internal microphone or a simple external microphone. It’s usually not intended to be the main audio used in the finished video.

Instead, it provides a record of what was happening during the take. For example, imagine filming an interview with a camera positioned several metres away from the subject.

The camera’s internal microphone might capture the conversation, but the recording could sound distant and contain considerable room ambience. Meanwhile, a dedicated microphone positioned close to the subject captures a much clearer recording.

The camera audio becomes the scratch track, while the external recording is used for the final dialogue.

Why Is Scratch Audio Useful for Synchronisation?

One of the biggest advantages of scratch audio is that it can help align separately recorded sound and picture. When a camera and an external audio recorder are running independently, their recordings need to be synchronised during editing.

Because both devices capture the same events, their audio waveforms contain corresponding patterns. Editing software can sometimes compare these patterns and automatically align the recordings.

For example, a hand clap produces a sharp sound that appears in both recordings. Once the waveforms are aligned, the editor can mute or remove the scratch audio and use the higher-quality recording instead.

How Does Automatic Audio Synchronisation Work?

Many video editing applications include tools that analyse audio waveforms to find matching sounds. The software compares the timing and shape of the recorded audio and attempts to identify the correct alignment.

This can save time when editing interviews, podcasts or productions involving multiple cameras. However, automatic synchronisation isn’t guaranteed to work in every situation.

If the camera’s scratch audio is extremely quiet, heavily distorted or missing important sounds, the software may struggle to find a reliable match. This is why it’s useful to make sure the camera captures a recognisable reference, even when you’re planning to replace the audio later.

Do You Still Need a Clapperboard?

A clapperboard provides a clear visual and audible synchronisation reference. When the clapper closes, the editor can match the visible point of contact with the sharp sound recorded by the microphones.

This remains useful even when automatic waveform synchronisation is available. For smaller productions, a simple hand clap can serve a similar purpose.

However, for more complicated shoots involving multiple cameras and audio devices, professional timecode systems may offer a more reliable workflow. Scratch audio, clapperboards and timecode can complement one another rather than being mutually exclusive.

Can Scratch Audio Ever Be Used in the Final Video?

Although scratch audio is usually replaced, there are situations where it might still be useful. For example, a camera microphone may capture environmental sounds that weren’t picked up by the main dialogue microphone.

These sounds could help establish the atmosphere of a location or provide additional material for sound design. However, scratch audio often contains more background noise and less detail than a properly positioned microphone.

It should therefore be evaluated carefully before being included in the final soundtrack.

How to Record Better Scratch Audio

Scratch audio doesn’t need to be perfect, but it should be clear enough to provide a useful reference. Make sure the camera microphone is enabled and the recording level is appropriate.

Avoid recording at extremely low levels, and check that the microphone isn’t completely obscured or disconnected. It’s also useful to create a clear synchronisation reference at the beginning of each take.

If you’re recording a long interview or podcast, periodically checking synchronisation can help identify problems before they become difficult to correct.

A Small Recording That Can Save Time

Scratch audio is a good example of how something that seems unimportant during filming can become valuable during editing. Even if the recording never appears in the finished video, it can make synchronisation and organisation considerably easier.

Once your dialogue is aligned and ready for the final mix, you can concentrate on music, ambience and sound design. If you’re looking for additional audio to complete your project, explore the RouteNote Licensing library for music and sound effects suited to different production styles.