Hum, Rumble, and similar low-frequency noise, can be reduced using the DeNoiseLF application.
Why DeNoise is not the right tool
DeNoise is a spectrally-based method, dividing the audio into 1024 frequency bands at the rate of 80 overlapping frames per second. For CD quality sound, each band has a width of about 22Hz, too coarse for the accurate resolution of low-frequency noise. In particular hum, which is at a fixed and sharply defined frequency, cannot be treated this way. Improving the frequency resolution would require dealing with frames in the order of 1 second length, whereas the effective treatment of hiss and similar noise demands a frame rate in the order of 80 per second.
How DeNoiseLF works
DeNoiseLF is not a spectrally-based method. It makes extensive use of wavelets to extract and treat the low-frequency audio content in a manner which achieves perfect reconstruction of the untreated higher-frequency content. The noisy audio signal is assumed to consist of the desirable audio and the undesirable low-frequency noise, simply mixed. Advanced statistical algorithms are used to estimate the two streams and remove the noise. The DeNoiseLF interface permits you to view both wave-form and spectral information about the audio and the treatment.
Broad-band noise versus Hum
DeNoiseLF has two mutually exclusive modes of operation.
• A "General" mode suited to the reduction of noise which is widely dispersed across the low-frequency spectrum.
• A "Hum" mode for the reduction of noise at a sharply defined frequency – however DeNoiseLF is not a notch filter.
DeNoiseLF is designed to be automatic, but the results may be monitored using headphones or speakers. Sound output can be selected to play the incoming untreated audio, the outgoing repaired audio, or the difference, which is what has been discarded as audible noise. Processing can be stopped at any time, so that the effect of different settings can be auditioned using a Preview function.