Computation of Immittance and Line Spectral Frequencies Based on Inter-frame Ordering Property

Abstract

Line spectral frequencies (LSF) and immittance spectral frequencies (ISF) are widely used in modern speech codecs based on autoregressive model. This paper addresses LSF and ISF calculation problems. The investigation of LSF/ISF placement on adjacent quasi-stationary frames is performed. It is shown that in majority of cases the inter-frame ordering property takes place. On this basis a new approach to LSF/ISF calculation is proposed. It is shown that LSF/ISF localization task is mainly reduced to verification of inter-frame ordering property. The computational expenses are reduced in 3.4 times in comparison with widely used Kabal’s method. Besides, the maximum number of operations is lower than the minimum expenses of accelerated Kabal’s method. The method is implemented on fixed-point DSP and showed stable performance.