Download Concatenative Sound Texture Synthesis Methods and Evaluation
Concatenative synthesis is a practical approach to sound texture synthesis because of its nature in keeping realistic short-time signal characteristics. In this article, we investigate three concatenative synthesis methods for sound textures: concatenative synthesis with descriptor controls (CSDC), Montage synthesis (MS) and a new method called AudioTexture (AT). The respective algorithms are presented, focusing on the identification and selection of concatenation units. The evaluation demonstrates that the presented algorithms are of close performance in terms of quality and similarity compared to the reference original sounds.
Download Signal Decorrelation using Perceptually Informed Allpass Filters
When a monophonic source signal is projected from two or more loudspeakers, listeners typically perceive a single, phantom source, positioned according to the relative signal amplitudes and speaker locations. While this property is the basis of modern panning algorithms, it is often desirable to control the perceived spatial extent of the phantom source, or to project multiple, separately perceived copies of the signal. So that the human auditory system does not process the loudspeaker outputs as a single coherent source, these effects are commonly achieved by generating a set of mutually decorrelated (e.g., statistically independent) versions of the source signal, which are then panned to make an extended source or multiple, independent source copies. In this paper, we introduce an approach to decorrelation using randomly generated allpass filters, and introduce numerical methods for evaluating the perceptual effectiveness of decorrelation algorithms. By using allpass filters, the signal magnitude is preserved, and the decorrelated copies and original signal will be perceptually very similar. By randomly selecting the magnitude and frequency of the poles of each allpass biquad section in the decorrelating filter, multiple decorrelating filters may be generated that maintain a degree of statistical independence. We present results comparing our approach (including methods for choosing the number of biquad sections and designing the statistics of the pole locations) to several established decorrelation methods discussed in the literature.
Download Complexity Scaling of Audio Algorithms: Parametrizing the MPEG Advanced Audio Coding Rate-Distortion Loop
Implementations of audio algorithms on embedded devices are required to consume minimal memory and processing power. Such applications can usually tolerate numerical imprecisions (distortion) as long as the resulting perceived quality is not degraded. By taking advantage of this error-tolerant nature the algorithmic complexity can be reduced greatly. In the context of real-time audio coding, these algorithms can benefit from parametrization to adapt rate-distortion-complexity (R-D-C) trade-offs. We propose a modification to the rate-distortion loop in the quantization and coding stage of a fixed-point implementation of the Advanced Audio Coding (AAC) encoder to include complexity scaling. This parametrization could allow the control of algorithmic complexity through instantaneous workload measurements using the target processor’s task scheduler to better assign processing resources. Results show that this framework can be tuned to reduce a significant amount of the additional workload caused by the ratedistortion loop while remaining perceptually equivalent to the fullcomplexity version. Additionally, the modification allows a graceful degradation when transparency cannot be met due to limited computational capabilities.
Download Non-Linear Identification of an Electric Guitar Pickup
Physical models of electric guitars are still not very widespread in the scientific literature. Especially, the description of the non linear behavior of pickups still requires some refinements. This paper deals with the identification of pickup non linearities based on a Hammerstein representation, by means of a specific experimental set-up to drive the pickup in a controlled way. A comparison with experimental results shows that the model succeeds in describing the pickup when used in realistic conditions.
Download Monophonic Pitch Detection by Evaluation of Individually Parameterized Phase Locked Loops
This paper describes a new efficient and sample based monophonic pitch tracking approach using multiple phase locked loops (PLLs). Hereby, distinct subband signals traverse pairs of individually parameterized PLLs. Based on the relation of the instantaneous pitch sample of respective PLLs to one another, relevant features per pitch candidate are derived. These features are combined into pitch candidate scores. Pitch candidates which exhibit the maximum score per sampling instance and exceed a voicing threshold, contribute to the overall pitch track. Evaluations with up to date datasets show that the tracking performance, compared to implementations which use only one PLL has significantly improved and nearly approaches the scores of a state of the art monophonic pitch tracker.
Download Piecewise Derivative Estimation of Time-Varying Sinusoids as Spline Exponential Functions
This paper discusses the estimation of non-stationary sinusoidal parameters. We formulate a piecewise version of the distributive derivative algorithm, which is used to analyse non-stationary sinusoidal signals and estimate their frequencies and log amplitude derivatives over a long duration as spline functions, and apply this algorithm for the estimation of instantaneous frequencies, amplitudes and phase angles. Test results show that the piecewise derivative algorithm provides better estimation than the previous non-piecewise version at lower computation cost.
Download The Fender Bassman 5F6-A Family of Preamplifier Circuits—A Wave Digital Filter Case Study
The Fender Bassman model 5F6-A was released in 1958 and has become one of the most revered guitar amplifiers of all time. It is the progenitor of a long line of related Fender designs in addition to inspiring Marshall’s first amplifier design. This paper presents a Wave Digital Filter study of the preamplifier circuit of 5F6-Abased amplifiers, utilizing recent theoretical advances to enable the simultaneous simulation of its four nonlinear vacuum tube triodes. The Dempwolf triode model is applied along with an iterative Newton solver to calculate the scattering at the 25 port R-type adapter at the root of the WDF tree. Simulation results are compared to “ground truth” SPICE data showing excellent agreement.
Download A Computational Model of the Hammond Organ Vibrato/Chorus using Wave Digital Filters
We present a computational model of the Hammond tonewheel organ vibrato/chorus, a musical audio effect comprising an LC ladder circuit and an electromechanical scanner. We model the LC ladder using the Wave Digital Filter (WDF) formalism, and introduce a new approach to resolving multiple nonadaptable linear elements at the root of a WDF tree. Additionally we formalize how to apply the well-known warped Bilinear Transform to WDF discretization of capacitors and inductors and review WDF polarity inverters. To model the scanner we propose a simplified and physically-informed approach. We discuss the time- and frequency-domain behavior of the model, emphasizing the spectral properties of interpolation between the taps of the LC ladder.
Download Resolving Grouped Nonlinearities in Wave Digital Filters using Iterative Techniques
In this paper, iterative zero-finding techniques are proposed to resolve groups of nonlinearities occurring in Wave Digital Filters. Two variants of Newton’s method are proposed and their suitability towards solving the grouped nonlinearities is analyzed. The feasibility of the approach with implications for WDFs containing multiple nonlinearities is demonstrated via case studies investigating the mathematical properties and numerical performance of reference circuits containing diodes and transistors; asymmetric and symmetric diode clippers and a common emitter amplifier.
Download RT-WDF — A Modular Wave Digital Filter Library with Support for Arbitrary Topologies and Multiple Nonlinearities
Wave Digital Filters (WDF) [1] are a popular approach for virtual analog modeling [2]. They provide a computationally efficient way to simulate lumped physical systems with well-studied numerical properties. Recent work by Werner et al. [3, 4] enables the use of WDFs to model systems with complicated topologies and multiple/multiport nonlinearities, to a degree not previously known. We present an efficient, portable, modular, and open-source C++ library for real time Wave Digital Filter modeling: RT-WDF [5]. The library allows a WDF to be specified in an object-oriented tree with the same structure as a WDF tree and implements the most recent advances in the field. We give an architectural overview and introduce the main concepts of operation on three separate case studies: a switchable attenuator, the Bassman tone stack, and a common-cathode triode amplifier. It is further shown how to expand the existent set of non-linear models to encourage custom extensions. Index Terms— wave digital filter, software, real time, virtual analog modeling, multiple nonlinearities