Why a lecture sounds worse on the recording than in the room
In the room, your brain locks on to the speaker and filters out the ventilation. A phone microphone hears everything at the level it arrives, and the voice loses about 6 dB each time the distance doubles, while the room’s noise and echo stay where they are. From the back of a lecture hall, the lecturer can end up barely louder than the projector fan.
- Sit near the front, or near a loudspeaker if the lecture is amplified.
- Put the phone on the desk, its bottom edge toward the speaker, rather than in a pocket or a bag.
- Keep it away from fans: a projector, a laptop, an air-conditioning vent.
- Put a folded jacket under it, so pens, elbows and typing on the desk don’t travel straight into the microphone.
Steady fans and ventilation are noises Noise Remover removes well (fan noise), and the typing of classmates taking notes comes down too, though less: in our lab test at full intensity, keyboard clicks dropped by 11.1 to 13.2 dB in the speaker’s pauses (how we measured).
Recording an hour or more on a phone
Noise Remover’s recorder keeps the screen on while it records and pauses when you switch to another app. For a long lecture during which you need your phone for something else, record with your phone’s own voice recorder app instead, then share the file to Noise Remover: the cleaning is the same.
Long files need room and time. Cleaning an hour of audio needs about 1.1 GB of free space while it runs for a mono recording, and twice that for stereo (the app checks before it starts and says how much to free), and takes several minutes, depending on the phone.
On the free plan, only the first 3 minutes of each file are cleaned, and an optional video extends one file to 15 minutes. A full lecture or meeting needs Pro, which cleans files of any length with no daily limit and no ads (see Free and Pro).
You do not have to watch it happen: leave the app while an hour-long recording cleans, and a notification shows the progress.
With Pro, batch cleaning takes a week of lectures in one go: select the files once, and find each of them cleaned in History.
Clean first, then transcribe or revise
Background noise is where automatic transcription tends to slip: a word masked by a fan becomes a guess. A cleaned track usually helps a transcription tool, and it is easier on your ears when you revise at a faster playback speed.
- Trim the dead time
Cut the minutes before the lecture starts and after it ends; the export keeps only the range between the handles.
- Check a question from the room
Voices far from the phone stay faint even once cleaned. Loudness normalization raises the whole recording to −16 LUFS; it does not raise a distant voice more than a near one.
- Export and send
Share the file to your transcription tool or your notes app, or save it to your phone. It is named after the original, with “(clean)” added.
Dictations work the same way: record the memo in the app, let it clean, and share it straight to your notes or to a transcription tool.
Clean your next lecture on your phone.
Free · Android 8.0 or later, 64-bit
Ask before you record
Many universities and schools have rules about recording lectures, and recording a meeting may require the consent of everyone in it, depending on the law where you are and your organization’s policy. Ask the lecturer or the participants before you start.
What you record stays on the phone: Noise Remover cleans without uploading anything and without an account, so a meeting about clients or a confidential project is never handed to an online service to be cleaned.
Rooms and situations it can’t fix
- Large, echoey rooms. Echo is not removed, so a voice recorded at the back of a hall stays distant. Moving closer is the only fix. See echo or background noise?
- Several people talking at once. In a lively discussion, the cleaning cannot pick out one voice, and overlapping voices can pull the main one down a little: in our lab test at full intensity, crowd chatter under the speaker lowered the speaker by 0.3 to 2.8 dB. If a cleaned voice comes out more than 6 dB quieter than the original, the app suggests a lower intensity.
- A voice as quiet as the noise. The noise goes, but the voice comes out thinner. Sitting closer helps more than any setting.
| Noise | Noise removed during pauses, in dB | Change in voice level |
|---|---|---|
| Broadband noise | 26 to 39 dB | −0.3 to −0.9 dB |
| Fan, air conditioning | 24 to 25 dB | −0.3 to −1.5 dB |
| Keyboard typing | 11 to 13 dB | 0.0 to −0.2 dB |
| Not what it is made for | ||
| Crowd chatter | 5 to 11 dB | −0.3 to −2.8 dB |