Discrete wavelet analysis of blade vortex interaction noise

The discrete wavelet transform, implemented in a multirate filter bank scheme using conjugate quadrature filters, is used to analyze blade vortex interaction (BVI) noise from helicopter rotors in different environments. The discrete wavelet transform successfully isolates the bursty, nonstationary nature of this impulsive noise source. The sub-band coding scheme is then used for signal reconstruction of only the portion of helicopter noise related to blade vortex interaction by filtering in the frequency and time domains. By eliminating extraneous noise sources, the wavelet analysis can produce a more direct comparison between BVI noise generated in flight and in other environments such as a wind tunnel.