FINDING LINE SPECTRAL FREQUENCIES USING THE FAST FOURIER TRANSFORM

Main-stream speech codecs are based on modelling the speech source by a linear predictor. An efficient domain for quantization and coding of this linear predictor is the line spectral frequency representation, where the predictor is encoded into an ordered set of frequencies that correspond to the roots of the corresponding line spectral polynomials. While this representation is robust in terms of quantization, methods available for finding the line spectral frequencies are computationally complex. In this work, we present a method for finding these frequencies using the FFT, including methods for limiting numerical range in fixed-point implementations. Our experiments show that, in comparison to a zero-crossing search in the Chebyshev domain, the proposed method reduces complexity and improves robustness, while retaining accuracy.