The present invention provides a fast Fourier transform processor, dynamic scaling method and fast Fourier transform with radix-8 algorithm. The variable-capacity outdoor unit has variable operation stages, which are changed based on the previous operation state and the current operation state. The front edge of the header wings are open to collect the sludge from the compressed zone along the floor of the settling tank while the rearward edges leading to the apex are provided with elastomeric sweeps to help move the collected sludge into the apex for removal therefrom.