Well, the forum crash seems to have eaten my last post.
I have made a noise filter to clean up audio signals live.
Other noise removal filters need to have a noise sample selected and try to remove that noise from the complete track - they only work offline.
This patch works online. It removes any stationary noise from the signal and doesn't need any user adjustment except that it does need to be told how much to reduce the noise.
"Stationary noise" is a signal whose frequency content and amplitude stay (more or less) constant for over 1 second. Fan hum is a good example, as well as the more or less "white" noise from the wind from the fan. Car motor sounds from a car travelling at constant speed is also a good example.
It will also kill feedback squeal cold, even at the lowest settings.
The patch is built in layers, and the lower layers can be used independently or combined and used to build different filters.
The attached zip file includes all the components from the lowest level up to a complete demonstation that takes in audio from a microphone and puts out filtered audio on line out. It also includes a set of help files that describe the function and use of the various modules.
NoiseLevelDetector.pd - estimates the amplitude of the stationary noise
NoiseFilter.pd - attenuates the signal based on the amplitude from
NoiseLevelDetector.pd Since it is more effective at high frequencies, it is best to feed it limited bandwidth signals and use multiple filters to cover the desired audio range.
BandLimitedNoiseFilter.pd - a Noisefilter that only works on the specified frequency range.
MultibandNoiseFilter.pd - a complete filter that covers the range from 40Hz upto 22000 hz to filter the complete audio spectrum.
Test.pd - demo program that demonstrates the use of MultibandNoiseFilter.pd
It works best for speaking voices. Singing tends to be more stationary. It could be adapted to singing voices by changing a single value in one of the lower level blocks.
The original idea was to create filter for removing car noises from microphone audio for two-way radios. When used to cover just the range from 300Hz to 3000Hz, it does a very good job.
The biggest disadvantage is that it will start making "musical noise" if there is a lot of noise and the attenuation is set high. It also adds a slight echoing quality to the filtered audio.
The project is hosted on GitHub: PureData NoiseFilter project.