Download Real-Time Wave Digital Simulation of Cascaded Vacuum Tube Amplifiers using Modified Blockwise Method
Vacuum tube amplifiers, known for their acclaimed distortion characteristics, are still widely used in hi-fi audio devices. However, bulky, fragile and power-consuming vacuum tube devices have also motivated much research on digital emulation of vacuum tube amplifier behaviors. Recent studies on Wave Digital Filters (WDF) have made possible the modeling of multi-stage vacuum tube amplifiers within single WDF SPQR trees. Our research combines the latest progress on WDF with the modified blockwise method to reduce the overall computational complexity of modeling cascaded vacuum tube amplifiers by decomposing the whole circuit into several small stages containing only two adjacent triodes. Certain performance optimization methods are discussed and applied in the eventual real-time implementation.
Download Time Warping in Digital Audio Effects
Time warping is an important paradigm in sound processing, which consists of composing the signal with another function of time called the warping map. This paradigm leads to different points of view in signal processing, fostering the development of new effects or the conception of new implementations of existing ones. While the introduction of time warping in continuous-time signals is in principle not problematic, time warping of discretetime signals is not self-evident. On one hand, if the signal samples were obtained by sampling a bandlimited signal, the warped signal is not necessarily bandlimited: it has a sampling theorem of its own, based on irregular sampling, unless the map is linear. On the other hand, most signals are regularly sampled so that the samples at non-integer multiples of the sampling interval are not known. While the use of interpolation can partly solve the problem it usually introduces artifacts. Moreover, in many sound applications, the computation already involves a phase vocoder. In this paper we introduce new methods and algorithms for time-warping based on warped time-frequency representations. These lead to alternative algorithms for warping for use in sound processing tools and digital audio effects and shed new light in the interaction of time warping with phase vocoders. We also outline the applications of time warping in digital audio effects.
Download Joint modeling of impedance and radiation as a recursive parallel filter structure for efficient synthesis of wind instrument sound
In the context of efficient synthesis of wind instrument sound, we introduce a technique for joint modeling of input impedance and sound pressure radiation as digital filters in parallel form, with the filter coefficients derived from experimental data. In a series of laboratory measurements taken on an alto saxophone, the input impedance and sound pressure radiation responses were obtained for each fingering. In a first analysis step, we iteratively minimize the error between the frequency response of an input impedance measurement and that of a digital impedance model constructed from a parallel filter structure akin to the discretization of a modal expansion. With the modal coefficients in hand, we propose a digital model for sound pressure radiation which relies on the same parallel structure, thus suitable for coefficient estimation via frequency-domain least-squares. For modeling the transition between fingering positions, we propose a simple model based on linear interpolation of input impedance and sound pressure radiation models. For efficient sound synthesis, the common impedance-radiation model is used to construct a joint reflectanceradiation digital filter realized as a digital waveguide termination that is interfaced to a reed model based on nonlinear scattering.
Download Interpretation and control in AM/FM-based audio effects
This paper is a continuation of our first studies on AM/FM digital audio effects, where the AM/FM decomposition equations were reviewed and some exploratory examples of effects were introduced. In the current paper we present more insight on the signals obtained with the AM/FM decomposition, intending to illustrate manipulations in the AM/FM domain that can be applied as interesting audio effects. We provide high-quality AM/FM effects and their implementations, alongside a brief objective evaluation. Audio samples and codes for real-time operation are also supplied.
Download High frequency magnitude spectrogram reconstruction for music mixtures using convolutional autoencoders
We present a new approach for audio bandwidth extension for music signals using convolutional neural networks (CNNs). Inspired by the concept of inpainting from the field of image processing, we seek to reconstruct the high-frequency region (i.e., above a cutoff frequency) of a time-frequency representation given the observation of a band-limited version. We then invert this reconstructed time-frequency representation using the phase information from the band-limited input to provide an enhanced musical output. We contrast the performance of two musically adapted CNN architectures which are trained separately using the STFT and the invertible CQT. Through our evaluation, we demonstrate that the CQT, with its logarithmic frequency spacing, provides better reconstruction performance as measured by the signal to distortion ratio.
Download A holistic glottal phase-related feature
This paper addresses a phase-related feature that is time-shift invariant, and that expresses the relative phases of all harmonics with respect to that of the fundamental frequency. We identify the feature as Normalized Relative Delay (NRD) and we show that it is particularly useful to describe the holistic phase properties of voiced sounds produced by a human speaker, notably vowel sounds. We illustrate the NRD feature with real data that is obtained from five sustained vowels uttered by 20 female speakers and 17 male speakers. It is shown that not only NRD coefficients carry idiosyncratic information, but also their estimation is quite stable and robust for all harmonics encompassing, for most vowels, at least the first four formant frequencies. The average NRD model that is estimated using data pertaining to all speakers in our database is compared to that of the idealized Liljencrants-Fant (LF) and Rosenberg glottal models. We also present results on the phase effects of linear-phase FIR and IIR vocal tract filter models when a plausible source excitation is used that corresponds to the derivative of the L-F glottal flow model. These results suggest that the shape of NRD feature vectors is mainly determined by the glottal pulse and only marginally affected by either the group delay of the vocal tract filter model, or by the acoustic coupling between glottis and vocal tract structures.
Download Sound morphologies due to non-linear interactions : towards a perceptive control of environmental sound-synthesis processes
This paper is concerned with perceptual control strategies for physical modeling synthesis of vibrating resonant objects colliding nonlinearly with rigid obstacles. For this purpose, we investigate sound morphologies from samples synthesized using physical modeling for non-linear interactions. As a starting point, we study the effect of linear and non-linear springs and collisions on a single-degreeof-freedom system and on a stiff strings. We then synthesize realistic sounds of a stiff string colliding with a rigid obstacle. Numerical simulations allowed the definition of specific signal patterns characterizing the non linear behavior of the interaction according to the attributes of the obstacle. Finally, a global description of the sound morphology associated with this type of interaction is proposed. This study constitutes a first step towards further perceptual investigations geared towards the development of intuitive synthesis controls.
Download Group Delay-Based Allpass Filters for Abstract Sound Synthesis and Audio Effects Processing
An algorithm for artistic spectral audio processing and synthesis using allpass filters is presented. These filters express group delay trajectories, allowing fine control of their frequency-dependent arrival times. We present methods for designing the group delay trajectories to yield a novel class of filters for sound synthesis and audio effects processing. A number of categories of group delay trajectory design are discussed, including stair-stepped, modulated, and probabilistic. Synthesis and processing examples are provided.
Download Assessing the Effect of Adaptive Music on Player Navigation in Virtual Environments
Through this research, we develop a study aiming to explore how adaptive music can help in guiding players across virtual environments. A video game consisting of a virtual 3D labyrinth was built, and two groups of subjects played through it, having the goal of retrieving a series of objects in as short a time as possible. Each group played a different version of the prototype in terms of audio: one had the ability to state their preferences by choosing several musical attributes, which would influence the actual spatialised music they listened to during gameplay; the other group played a version of the prototype with a default, non-adaptive, but also spatialised soundtrack. Time elapsed while completing the task was measured as a way to test user performance. Results show a statistically significant correlation between player performance and the inclusion of a soundtrack adapted to each user. We conclude that there is an absence of a firm musical criteria when making sounds be prominent and easy to track for users, and that an adaptive system like the one we propose proves useful and effective when dealing with a complex user base.
Download Modeling and Rendering for Virtual Dropping Sound based on Physical Model of Rigid Body
Sound production by means of a physical model for falling objects, which is intended for audio synthesis of immersive contents, is described here. Our approach is a mathematical model to synthesize sound and audio for animation with rigid body simulation. To consider various conditions, a collision model of an object was introduced for vibration and propagation simulation. The generated sound was evaluated by comparing the model output with real sound using numerical criteria and psychoacoustic analysis. Experiments were performed for a variety of objects and floor surfaces, approximately 90% of which were similar to real scenarios. The usefulness of the physical model for audio synthesis in virtual reality was represented in terms of breadth and quality of sound.