Abstract
A sound recording of a plucked string instrument is encoded and resynthesized using two stages of prediction. In the first stage of prediction, a simple physical model of a plucked string is estimated and the instrument excitation is obtained. The second stage of prediction compensates for the simplicity of the model in the first stage by encoding either the instrument excitation or the model error using warped linear prediction. These two methods of compensation are compared with each other, and to the case of single-stage warped linear prediction, adjustments are introduced, and their applications to instrument synthesis and MPEG4's audio compression within the structured audio format are discussed.
Highlights
Since the discovery of the Karplus-Strong algorithm [1] and its subsequent reformulation as a physical model of a string, a subset of the digital waveguide [2], physical modelling has seen the rapid development of increasingly accurate and disparate instrument models
This paper proposes a solution to this real-time parameterization and coding problem for string modelling in the marriage of two common techniques, the basic plucked string physical model and warped linear prediction (WLP) [12]
Informal listening tests suggested that the WLPCMX topology offered slightly improved sound quality and a more musical coding at lower bit rates, it came at the cost of a much brighter timbre
Summary
Since the discovery of the Karplus-Strong algorithm [1] and its subsequent reformulation as a physical model of a string, a subset of the digital waveguide [2], physical modelling has seen the rapid development of increasingly accurate and disparate instrument models. This paper proposes a solution to this real-time parameterization and coding problem for string modelling in the marriage of two common techniques, the basic plucked string physical model and warped linear prediction (WLP) [12]. The justifications for this approach are as follows. While residual quantization noise in a warped predictive codec is shaped so as to be masked by the signal’s spectral peaks [12], in one of the proposed topologies, the noise in the physical model’s excitation signal is likewise shaped into the modelled harmonics This shaping of the noise by the physical model results in distortion that, if audible, is neither unnatural nor distracting, thereby allowing codec sound quality to degrade gracefully with decreasing bit rate.
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