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Ground loops

Find and fix the ground loop behind a hum.

A ground loop puts hum into everything you record through it. Break it for the next take, and drop a recording you already made to hear its hum notched out.

Drop a recording with hum

Solipsium checks it in your browser for clipping, hum and noise, without uploading it. It can then repair the first 20 seconds for you to hear, with no account.

WAV, MP3, M4A, MP4 and more, up to five minutes for the check.

Choose a recording

Finding it

Two paths to ground make a loop.

When two pieces of gear connect to each other and each to the mains, a little current flows round the loop, and you hear it at 50 or 60 Hz.

  1. Unplug one cable at a time.

    Start with the computer, the interface, the mixer and the speakers connected, then take out one audio cable at a time. The hum stops when the loop is broken.

  2. Run a laptop on its battery.

    If the hum stops when the charger is out, the loop runs through the charger.

  3. Use one outlet.

    Plug the computer, the interface and the speakers into the same outlet or power strip, so they share one ground.

Breaking it safely

Break the audio path, never the safety ground.

Never cut or tape over the earth pin of a power plug. It is there to keep you safe.

A ground lift on the audio side.

A DI box or an audio isolator with a ground lift switch breaks the loop in the signal cable, not in the power.

A USB isolator.

When the loop runs through a USB cable, an isolator between the computer and the interface breaks it there.

The hum already recorded.

Lines at 50 or 60 Hz and their multiples that stand 10 dB over the frequencies around them are notched out in bands 3 Hz wide, the first four harmonics always and higher ones up to the 24th where they stand 8 dB out: “Mains hum was found, so it is notched out before any cleanup.”

Questions

About ground loops.

Is it hum or buzz?

Both. Hum is the line at the mains frequency; buzz is the same line with strong harmonics. The repair notches the harmonics that stand out along with it.

The hum comes and goes.

Hum in parts of a recording is notched only where it plays: “Mains hum was found in parts of the recording, so it is notched out there; the voice is put back wherever the notches removed nothing.”

Will notching it change my voice?

A little: the notches also cut the voice's own sound at the hum's frequencies, in bands 3 Hz wide. Compare Original and Repaired on the same words.

Which countries are 50 and which are 60?

North America and parts of South America and Asia use 60 Hz; most of Europe, Africa, Asia and Australia use 50 Hz. The check in your browser names the frequency it finds.

A buzz with no steady line?

A buzz with no steady 50 or 60 Hz line under it is not labelled hum, and neither is a tone at another frequency.

Is my recording uploaded?

Not for the check, which runs in your browser. Pressing Repair the first 20 seconds sends those 20 seconds; when your browser could not open the file, or it runs over five minutes, the file itself goes to Solipsium's server, so the try is offered for it only up to 25 MB. Solipsium keeps only the first 20 seconds and deletes them within an hour. If you are signed in, a file you drop or choose is uploaded to your account and opens in the editor instead. The privacy notice has the rest.

Free audio tools

Related free tools.

For hum and the gear around it.

The whole recording.

Make a free account and drop the same file into the editor to repair all of it, up to 30 minutes at a time.

Repair the whole recording

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