From beginning to end of signal clean from noise.how fft works?to filter noise from signal.and what kind operation its?
Audio de-noising is usually achieved using a multi-band "expander". Expanders are dynamics controls that are best understood as the 'opposite' of a 'compressor'.
Typical dynamics controls work on between 1 and 6 bands for normal compression/expansion operations. Denoising expanders might work on hundreds of bands depending on the complexity of the denoiser.
The use of an FFT will depend entirely on the design of the expander stage.