Why the bleep is 1 kHz
Broadcast studios line up their audio with a steady 1 kHz test tone, so a 1 kHz oscillator has always been within reach of any TV or radio engineer. Dropping that tone over a word is the quickest way to hide it, and 1 kHz sits where hearing is sensitive and speech carries much of its detail, so the beep is impossible to miss. That is the usual explanation for why the censor beep sounds the way it does; there was never a formal standard for it.
The same tone is useful far beyond censoring: as a line-up test tone, a sync beep at the start of a recording, or a placeholder sound effect. If you need other beeps and alerts, try the alarm generator.
How long a bleep should be
Match the word, not a fixed length. A bleep that stops early lets the end of the word through; one that runs long swallows the next word too. Single words usually last a few hundred milliseconds, so start around 300 to 600 ms and adjust by ear. For a comic effect, a longer bleep over a whole phrase also works.
Keep the fades short. A few milliseconds of fade in and out stops the beep clicking without softening it; longer fades make it sound more like a tone than a bleep. The level should be about as loud as the speech it replaces, so it does not jump out of the mix.
Bleeping in a video editor
- Set the length to roughly the word you need to cover and download the beep as WAV.
- Import it into your editor and place it on a free audio track, lined up with the word.
- Cut or mute the dialogue under the beep (a razor cut either side of the word, then delete or mute that piece).
- Trim the beep clip so it starts and ends with the word, and play it back.
If you only have the audio, it is often quicker to do the whole job here: load the file in the bleep editor above, select each word on the waveform, add it, and export the whole file as WAV or MP3. To cut parts out instead of bleeping them, use the audio trimmer.