Sylvain Marchand

Comparing the order of a polynomial phase model for the synthesis of quasi-harmonic audio signals

Sinusoidal modeling has been successfully applied to a wide range of audio signal processing problems, such as coding or time and frequency stretching. While many methods have been proposed for the analysis part of the process, it seems that there is some general agreement concerning the synthesis part in the nonoverlapping case: It is very often achieved by using the well-known McAulay-Quatieri method, which consists of an order 3 polynomial reconstruction of the phases of the sinusoidal model partials. We compare this classical approach with both a simpler (order 1, that is, linear interpolation) and a more complex (order 5) polynomial model for phase interpolation of quasi-harmonic signals. A gain has been measured in the signal-to-noise ratio at the synthesis stage, although the performance is limited by the amplitude model and by the imprecision in the analysis stage.

Informed spectral analysis: audio signal parameter estimation using side information

Parametric models are of great interest for representing and manipulating sounds. However, the quality of the resulting signals depends on the precision of the parameters. When the signals are available, these parameters can be estimated, but the presence of noise decreases the resulting precision of the estimation. Furthermore, the Cramér-Rao bound shows the minimal error reachable with the best estimator, which can be insufficient for demanding applications. These limitations can be overcome by using the coding approach which consists in directly transmitting the parameters with the best precision using the minimal bitrate. However, this approach does not take advantage of the information provided by the estimation from the signal and may require a larger bitrate and a loss of compatibility with existing file formats. The purpose of this article is to propose a compromised approach, called the informed approach,’ which combines analysis with (coded) side information in order to increase the precision of parameter estimation using a lower bitrate than pure coding approaches, the audio signal being known. Thus, the analysis problem is presented in a coder/decoder configuration where the side information is computed and inaudibly embedded into the mixture signal at the coder. At the decoder, the extra information is extracted and is used to assist the analysis process. This study proposes applying this approach to audio spectral analysis using sinusoidal modeling which is a well-known model with practical applications and where theoretical bounds have been calculated. This work aims at uncovering new approaches for audio quality-based applications. It provides a solution for challenging problems like active listening of music, source separation, and realistic sound transformations.