  A two-step enhancement method based on spectral subtraction and phase
spectrum compensation is presented in this paper for noisy speeches in adverse
environments involving non-stationary noise and medium to low levels of SNR.
The magnitude of the noisy speech spectrum is modified in the first step of the
proposed method by a spectral subtraction approach, where a new noise
estimation method based on the low frequency information of the noisy speech is
introduced. We argue that this method of noise estimation is capable of
estimating the non-stationary noise accurately. The phase spectrum of the noisy
speech is modified in the second step consisting of phase spectrum
compensation, where an SNR-dependent approach is incorporated to determine the
amount of compensation to be imposed on the phase spectrum. A modified complex
spectrum is obtained by aggregating the magnitude from the spectral subtraction
step and modified phase spectrum from the phase compensation step, which is
found to be a better representation of enhanced speech spectrum. Speech files
available in the NOIZEUS database are used to carry extensive simulations for
evaluation of the proposed method.
