Pitch Shifting of Music Based on Adaptive Order Estimation of Linear Predictor

A method for timbre-preserving pitch shifting of music signals based on estimating the order in linear predictive coding (LPC) is described. LPC is used for estimating a transfer function approximated using autoregressive (AR) models. We need to determine the appropriate number of poles in the AR model for LPC. For general audio signals, the number of poles varies with time because the number and the kind of sound sources such as musical instruments change dynamically. To estimate the order, we utilize the inequality of arithmetic and geometric means (AM-GM inequality) and fractional bandwidth at each pole of the model. The estimated order can be applied to LPC for the timbre-preserving pitch shifting. A listening test evaluated by the mean opinion score (MOS) shows that our approach improves the sound quality of pitch-shifted signals.