ESUS

Extended Subtractive Synthesis of Audio Signals

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 Obiettivo del progetto (Objective)

'The purpose of this proposal is to generalize the subtractive sound synthesis method for digital audio applications. Whereas the basic idea of Additive Synthesis consists in adding the sinusoidal components of a Fourier series, the analog Subtractive Synthesis aims to imitate a given periodic sound by filtering a fixed excitation signal (usually square, triangle or sawtooth signals). With this source-filter principle, the spectral envelope is reproduced by designing the filter. For some decades, the Additive Synthesis has been significantly improved for computer applications, but the Subtractive Synthesis not. Actually, on one hand, the recent digital subtractive synthesizers focus on modelling old analog synthesizers since the 1960s (from which the Moog is the most popular), and on the other hand, the source-filter principle has been improved for the particular case of the speech coding and synthesis only. Here, we plan to apply recent advances of the audio processing field to derive a new Extended Subtractive Synthesis method. For example, we will study the use of time-varying filters and pitch trajectories to reproduce transients, modulations and roughness. With learning from recorded sounds, we will estimate the parameter trajectories. Moreover, we will use knowledge about psychoacoustics to imitate the original sound from a perceptual viewpoint. This new synthesis technique will have applications in sound synthesis of harmonic musical sounds, and we plan also to synthesize animal sounds. The new method will also be useful for computer game audio. Moreover, most of usages of current Additive Synthesis could be applied, such as time or frequency stretching or noise removal. The main benefits of the Subtractive Synthesis are the reduced number of parameters and the easier control of the resynthesis.'

Introduzione (Teaser)

Generally, computer music is any music constructed, reproduced or performed with the aid of computer technology. The term usually refers to real-time music that computer software generates based on a predetermined set of constraints.

Descrizione progetto (Article)

Real-time music generated by computers often relies on technologies such as synthesis and digital signal processing. These technologies, wrapped up in or connected to specific software programmes, arrange sequences of individual sounds, note durations and pitches.

Computer music is definitely established in the contemporary musical world, whether it is for recording, mixing, composing or playing new (virtual) instruments. Digital techniques of sound analysis, synthesis, transformation and coding are now commonly used in many other ways. They are, for example, used in telecommunications, mobile technology, movies and video games.

Elaborating on this demand, a new digital audio synthesis technique (or the generalisation of the subtractive synthesis) has been developed. Called Extended Subtractive Synthesis (ESUS), it satisfies sound realism thanks to recent advances in the audio signal processing field.

This project, 'Extended subtractive synthesis of audio signals' (ESUS), studied the use of time-varying filters and pitch trajectories to reproduce transients, modulations and roughness. The researchers generalised the subtractive sound synthesis method for digital audio applications.

As a result of the study, three tools have been proposed for spectral envelope estimation, perceptual smoothing and perceptual filter approximation. All these can impact other audio applications (such as speech coding, audio enhancement and digital audio effects) as well as other topics in signal processing or mathematics.