Remove DC Offset

How it works

1. Choose an audio file.
2. Read the measured offset for each channel.
3. Remove it and compare the waveform.
4. Export and download.

What DC offset is

In a healthy recording the waveform swings equally above and below zero. DC offset means the whole waveform sits a little above or below that line, usually because of a fault in a sound card or recorder. You cannot hear it directly, but it wastes headroom, can make a click where audio is cut or joined, and makes processing such as compression and normalization behave less well.

The page measures the offset of every channel as a share of full scale and in dBFS, and measures the exported file again so you can see it removed.

Two methods

Subtract the average measures the mean of each channel over the part being processed and subtracts it. It is exact for an offset that stays the same, and it changes nothing else about the sound.

High-pass at 5 Hz uses a very gentle filter that follows an offset which drifts slowly over the recording. It also removes anything below 5 Hz, which is inaudible, and a constant offset fades out over the first fraction of a second of the file instead of vanishing at once.

Limits

Offsets smaller than 0.05 percent of full scale are reported as negligible. Removing the offset moves the waveform but does not change loudness. A file that is clipped stays clipped.

Questions