Where hiss comes from
Every microphone and every amplifier adds a faint random noise of its own, produced by the electronics themselves. In a good setup it sits far below the voice. It turns into audible hiss when something forces the recording to amplify a weak signal:
- Distance. Record from across the room and the phone raises its gain to hear you, lifting its own hiss along with your voice.
- High input gain on an external microphone or recorder, turned up to make a quiet voice louder.
- Inexpensive microphones and lavaliers, whose self-noise is higher to begin with.
- Long extension cables, which weaken the signal before it reaches the input.
- Old recordings: tape hiss from cassettes and the noise of early voice recorders, digitised years later.
People call it hiss, static or white noise. Strictly, white noise has equal energy at every frequency and sounds like a bright “shhh”; pink noise, which falls off toward the highs, sounds softer, closer to steady rain. Both are broadband: they cover the whole range of the voice at once.
Why a filter can’t remove hiss without dulling the voice
An equaliser or a filter removes frequencies, everywhere and all the time. Hiss lives at every frequency the voice uses, and it is most audible in the highs, exactly where the consonants s, f, t and sh carry their detail. Cut the treble to lose the hiss and those consonants go with it: the voice turns muffled, as if recorded through a pillow.
A noise gate, the other classic tool, mutes the recording whenever nobody speaks. It cleans the pauses, but the hiss returns with every word, so the background seems to switch on and off. Noise reduction, noise gate and EQ compared.
How a neural model handles hiss
Noise Remover runs RNNoise, a neural network trained on speech, which does what a filter cannot: decide, for each moment and each frequency band, how much is voice. Every 10 ms it splits the sound into 32 bands. Where a vowel’s harmonics rise out of the hiss, the band is kept; where only hiss is left, it is turned down; between words, every band goes down at once. Its gains are not allowed to drop abruptly from one frame to the next, which avoids the chopped sound of a gate.
In our lab test at full intensity, white-noise hiss dropped by 23 to 43 dB in the speaker’s pauses, and broadband pink noise by 26 to 39 dB, while the voice moved by 0.9 dB at most. Overall quality measured by DNSMOS rose from “bad” or “poor”, around 1.2 to 2.3 out of 5 at the three loudest noise levels, to about 3 out of 5. How we measured.
| Noise | Noise removed during pauses, in dB | Change in voice level |
|---|---|---|
| Hiss, white noise | 23 to 43 dB | −0.2 to −0.6 dB |
| Broadband noise | 26 to 39 dB | −0.3 to −0.9 dB |
Settings for a hissy recording
- Judge it on headphones
Hiss is high and quiet, and a phone speaker hides much of it. Listen through headphones, first to a pause, then to a sentence.
- Raise the intensity for loud hiss
If a “shhh” remains between words, slide toward 100%. At 80%, the reduction is held near 29 dB on purpose, which is less than the model can take off a loud hiss.
- Watch the s sounds
If your s and f sounds turn soft or lispy, you have gone a step too far for this recording: come back down by 10%.
- Get the intensity right before the level
A distant, hissy recording is usually quiet too. The ready-to-publish level lifts the cleaned mix toward −16 LUFS, and whatever hiss is left rises with the voice.
The 80 Hz low-cut filter makes little difference to hiss, which is mostly high; leave it on for any rumble underneath.
Remove the hiss from your recording on the phone.
Free · Android 8.0 or later, 64-bit
How to record with less hiss
- Get closer instead of turning up the gain. Halving the distance to your mouth raises your voice by about 6 dB against the same hiss, while raising the gain lifts both together.
- Hold the phone 15 to 30 cm away, with its microphone end pointing at your mouth rather than at the ceiling.
- Put the microphone near your mouth. A clip-on microphone on your chest, even an inexpensive one, usually ends up with less hiss than a phone on the table, because it needs far less gain.
- Keep cables short. Avoid long, cheap extension cables between a microphone and the phone.
- Leave boosts off. If a recording app or recorder offers a gain or boost setting, keep it as low as still gives a clear level.
In Noise Remover’s own recorder, you can pick the microphone you record with on Android 10 or later: the phone’s, a wired or USB microphone, or a Bluetooth one.