How to clean up a lecture or class recording
To clean up a lecture recording, import it into Denoise, keep the default AI · Auto engine and tap Denoise: an AI model on your phone removes ventilation hum, chatter and hiss so the speaker is easier to follow, and it rebuilds the missing highs of a muffled, phone-quality recording on its own. To save time when you go over it again, AI · Shorten can then cut a 73-minute lecture to about 50 minutes.
Last updated · By Routes Software, the makers of Denoise
Clean up a lecture in three steps
Import the recording
Tap + › Import from Files (or Import from Gallery for a video), or share it to Denoise from Voice Memos or your recorder app. Hour-long files are fine: there is no length limit.
Tap Denoise
Keep AI · Auto and tap Denoise. It takes about 5 to 10 seconds per minute of audio on a recent phone, so an hour-long lecture takes several minutes.
Listen and save
Compare Original and Cleaned at a few points, then tap Share Cleaned or Save to Files…. For a shorter version, choose AI · Shorten and tap Shorten.
Hear the difference
Good to know
- Denoise brings out speech that is under the noise; it does not rebuild words that were never recorded. A lecturer who is barely audible from the back row becomes clearer, not studio-quality.
- Echo in a large hall is reduced less than steady noise such as air conditioning.
- Need the text? Keep the default Denoise strength rather than the maximum: in our test, audio cleaned at full strength cost a speech recognizer more words than a lighter clean (Clean audio before transcribing).
Frequently asked questions
Can I clean a recording made on a laptop or a separate recorder?
Yes. Move the file to your phone (AirDrop, Files, Google Drive or a cable) and import it. M4A, MP3 and WAV files work, and so do MP4 and MOV videos.
Can I record the lecture in Denoise?
Yes. Tap + and choose Recorder: recording continues with the screen locked, a call only pauses it, and Denoise removes the noise as soon as you stop (Record without background noise).
Can it make the lecture shorter?
Yes. AI · Shorten trims the long pauses and speeds up the speech a little without changing the voice; a 73-minute lecture comes out at about 50 minutes.
Does it work offline?
Yes. Everything runs on your phone, so it works in a lecture hall without Wi-Fi, and the recording is never uploaded.
Is it free?
Importing, cleaning and listening are free, with no account. Saving or sharing the result is paid: 3 exports cost $1.99, and Denoise Pro $2.99 a month or $14.99 once ($11.99 on Google Play). These are US prices from October 2026; the store shows yours before you pay.