Jonathan Abel | Stanford University (original) (raw)

Papers by Jonathan Abel

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Virtual analog effects are a consequence of the ongoing digitization of all equipment used in mus... more Virtual analog effects are a consequence of the ongoing digitization of all equipment used in music production. Various digital methods to imitate the warm or lo-fi sound qualities that remind listeners of analog times are covered in this chapter. In particular, many algorithms presented in this chapter are physical models of audio effect boxes that have been traditionally analog electronic or electromechanical devices, such as voltage-controlled filters and spring reverberation units. Some algorithms, for instance the telephone sound ...

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Journal of the Acoustical Society of America, Jul 1, 2021

A signal processing method to impart the response of an acoustic string instrument to an electric... more A signal processing method to impart the response of an acoustic string instrument to an electric instrument that includes frequency-dependent string decay alterations is proposed. This type of processing is relevant when trying to make a less resonant instrument, such as an electric guitar, sound similar to a more resonant instrument, such as acoustic guitar. Unlike previous methods which typically only perform equalization, our method includes detailed physics-based string damping changes by using a time-varying filter which adds frequency-dependent exponential damping. Efficient digital filters are fit to bridge admittance measurements of an acoustic instrument and used to create equalization filters as well as damping correction filters. The damping correction filters are designed to work in real-time as they are triggered by onset and pitch detection of the signal measured through an under-saddle pickup to determine the intensity of the damping. A test case is presented in which an electric guitar is processed to model a measured acoustic guitar.

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2015 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA), 2015

A general, explicit, and novel formulation for Wave Digital Filters (WDFs) with multiple/multipor... more A general, explicit, and novel formulation for Wave Digital Filters (WDFs) with multiple/multiport nonlinearities is presented. It confronts graph-theoretic views of WDF structures (SPQR tree) with techniques from the nonlinear loop resolution literature (the K method) and a novel method for deriving scattering matrices (WDF adaptors) of arbitrarily complex topologies. It accommodates any number of memoryless nonlinearities with any number of ports each without requiring simplifying assumptions. A case study on the first clipping stage of the Big Muff Pi distortion pedal is presented. This circuit, with its multiple nonlinearities, multiport nonlinearity, and complicated topology, poses an intractable problem for state-of-the-art WDF methods. Hence, successful simulation of this circuit demonstrates the novelty and robustness of our framework.

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A recording technique due to Walter Murch for extending the reverberation time of a room is analy... more A recording technique due to Walter Murch for extending the reverberation time of a room is analyzed, and a realtime implementation is presented. The technique involves speeding up a prerecorded dry sound and playing it into a room. The room response is recorded and subsequently slowed down such that the original signal appears at its normal speed, while the reverberation of the room is ‘stretched,’ causing the room to sound larger than it is. A signal analysis is presented showing that this process is equivalent to slowing down the impulse response of the room. Measurements on a simple physical system confirm this effect, and show that the process can be interpreted as either scaling the room dimensions, or slowing the speed of sound. Finally, we describe a block processing approach which implements this technique in real time with a fixed processing latency.

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We present a Modified-Nodal-Analysis-derived method for developing Wave Digital Filter (WDF) adap... more We present a Modified-Nodal-Analysis-derived method for developing Wave Digital Filter (WDF) adaptors corresponding to complicated (non-series/parallel) topologies that may include multiport linear elements (e.g. controlled sources and transformers). A second method resolves noncomputable (non-tree-like) arrangements of series/parallel adaptors. As with the familiar 3-port series and parallel adaptors, one port of each derived adaptor may be rendered reflection-free, making it acceptable for inclusion in a standard WDF tree. With these techniques, the class of acceptable reference circuits for WDF modeling is greatly expanded. This is demonstrated by case studies on circuits which were previously intractable with WDF methods: the Bassman tone stack and Tube Screamer tone/volume stage.

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Journal of The Audio Engineering Society, 2010

Ribbon microphones are known for their warm sonics, owing in part to the unique ribbon motion ind... more Ribbon microphones are known for their warm sonics, owing in part to the unique ribbon motion induced by the sound field. Here the motion of the corrugated ribbon element in a sound field is considered, and a physical model of the ribbon motion is presented. The model separately computes propagating torsional disturbances and coupled transverse and longitudinal disturbances. Each propagation mode is implemented as a mass-spring model where a mass is identified with a ribbon corrugation fold. The model is parameterized using ribbon material and geometric properties. Laser vibrometer measurements are presented, revealing stiffness in the transverse and longitudinal propagation, and showing close agreement between measured and modeled ribbon motion.

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The problem of providing an audible separation of mixed sound sources is important for a number o... more The problem of providing an audible separation of mixed sound sources is important for a number of applications, including speech recognition, noise reduction in communication channels, re-mixing of recorded music, and using environmental sound in musical compositions and film scores, as well as applications in environmental noise control. Many approaches to the problem have been investigated, each with application in a specific area. This paper presents a novel approach that would have application where: a) high-quality reproduction is desired with minimum artifacts; b) measurement using a multiple-microphone array is possible; and c) real-time performance is not required. As such it would apply particularly to audio-oriented applications, but may also have application in environmental noise. The technique involves a constrained least-squares decomposition of spectrogram values recorded at multiple microphones, together with an optional adaptive filtering step. Performance of the a...

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The Journal of the Acoustical Society of America, 2020

A real-time method of string instrument acoustic transfer which includes damping is proposed. Aco... more A real-time method of string instrument acoustic transfer which includes damping is proposed. Acoustic transfer of string instruments is relevant when trying to make a non-resonant instrument, such as an electric guitar, sound more similar to an acoustic guitar. Unlike previous acoustic transfer methods which only perform equalization, this method includes damping changes by using a time-varying filter which adds frequency-dependent exponential damping. Efficient digital filters are fit to bridge admittance measurements of an acoustic guitar and used to create equalization filters as well as damping correction filters. The damping correction filters work in real-time as they are triggered by onset and pitch detection of the signal measured through an under saddle pickup to determine the intensity of the damping.

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EURASIP Journal on Advances in Signal Processing, 2011

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Journal of the Acoustical Society of America, Oct 1, 2022

Due to geological closures between 21 000 and 29 000 years ago, the acoustics of the UNESCO World... more Due to geological closures between 21 000 and 29 000 years ago, the acoustics of the UNESCO World Heritage site, Chauvet Cave (Ardèche, France) have been in slow flux via mineral deposition processes that continue to alter its interior. Since Upper Paleolithic humans created extensive and elaborate artworks throughout this grand limestone cavern more than 30 000 years ago, the cave’s interior has changed with calcite and other minerals forming a diversity of features including the best-known stalactites, stalagmites, and flowstone floor coverings. Here, we report on archaeoacoustics fieldwork in 2022 that initiated acoustical mapping and reconstructive modeling to enable archaeological acoustics research and the creation of auralizations and multimodal experiences for virtual public access to this conservation-restricted place. We present here a comparative room acoustics study of two substantively enclosed cave areas (Salle du Fond and Galerie du Cactus) whose volumes differ significantly, but whose extant reverberation times are similar across most center bands, providing important information about the dynamical contributions of surface materials and structural features distinct to each impulse-response-measured location. Our study exemplifies an archaeological application of room acoustics methods with site-responsive techniques that offer a human-centered approach for understanding and translating cultural heritage acoustics across time.

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Proceedings of the SMC Conferences, Sep 14, 2014

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When a monophonic source signal is projected from two or more loudspeakers, listeners typically p... more 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 ...

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We present an analysis of the cowbell voice circuit from the Roland TR-808 Rhythm Composer. A dig... more We present an analysis of the cowbell voice circuit from the Roland TR-808 Rhythm Composer. A digital model based on this analysis accurately emulates the original. Through the use of physical and behavioral models of each sub-circuit, this model supports accurate emulation of circuit-bent extensions to the voice's original behavior (including architecture-level alterations and component substitution). Some of this behavior is very complicated and is inconvenient or impossible to capture accurately through black box modeling or structured sampling. The band pass filter sub-circuit is treated as a case study of how to apply Mason's gain formula to finding the continuous-time transfer function of an analog circuit.

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ABSTRACT One dimensional digital waveguides are widely used to model travelling pressure waves al... more ABSTRACT One dimensional digital waveguides are widely used to model travelling pressure waves along wind instrument bores. These models must also account for frequency-dependent losses occurring along the bore walls, and at boundaries. This is accomplished by incorporating waveguide filter elements, which are based on the widely accepted theory describing these losses. A measurement technique is demonstrated that allows the effects of each waveguide element to be isolated and observed for simple cylindrical and conical tube structures, as well as their combination. This measurement system yields data that closely matches the theory and provides confidence that it may be extended to accurately measure musical instrument bores, where bore shapes are usually considerably less simple, and thus more difficult to account for theoretically. This work paves the way for further application to clarinet and trumpet bores.

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A reed, or more generally, a pressure-controlled valve, is the primary resonator for many wind in... more A reed, or more generally, a pressure-controlled valve, is the primary resonator for many wind instruments and vocal systems. In physical modeling synthesis, the method used for simulating the reed typically depends on whether an additional upstream or downstream pressure causes the corresponding side of the valve to open or close further. In this work, a generalized and configurable model of a pressure controlled valve is presented, allowing the user t o design a reed simply by setting the model parameters. The parameters are continuously variable, and may be config- ured to produce blown closed models (like woodwinds or reed-pipes), blown open models (as in simple lip-reeds, the human larynx, harmonicas and harmoniums) and sym- metric "swinging door" models. This generalized virtual reed affords the musician the ability to produce a wide va- riety of sounds which would otherwise only be obtained with several reed instruments.

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The Journal of the Acoustical Society of America, 2008

The control of virtual musical instruments often relies on either a specially-developed controlle... more The control of virtual musical instruments often relies on either a specially-developed controller on which the performer has usually not gained sufficient virtuosity to play musically, or an existing multipurpose general controller with control parameters not always easily, or intuitively, mapped to the synthesis parameters of the virtual instrument being performed. A response to this problem is to obtain control information from a musical performance where the performer uses an instrument with which s/he is sufficiently familiar. In this work, we incorporate a previously developed measurement technique to transform a measured clarinet signal into a sequence of pulses corresponding to the reed displacement as a function of time. The measurement technique, shown to obtain accurate reflection functions from various tube structures, is used to obtain a filter modeling the bore and bell of the wind instrument used in the performance. The "reed pulse" waveform is then isolated...

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Journal of the Acoustical Society of America, Jul 1, 2021

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2015 IEEE Workshop on Applications of Signal Processing to Audio and Acoustics (WASPAA), 2015

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Journal of The Audio Engineering Society, 2010

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The Journal of the Acoustical Society of America, 2020

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EURASIP Journal on Advances in Signal Processing, 2011

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Journal of the Acoustical Society of America, Oct 1, 2022

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Proceedings of the SMC Conferences, Sep 14, 2014

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The Journal of the Acoustical Society of America, 2008

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We designed models of three TR-808 voice circuits which are physically-informed and derived as cl... more We designed models of three TR-808 voice circuits which are physically-informed and derived as closed-form expressions in terms of electrical component values where possible. An important part of the performance practice of analog drum machines involves modifying their voices circuits. These techniques would be impossible to recreate in a digital model through structured sampling or black-box modeling. Our physically-informed models are designed to respect this practice by allowing changes to the circuit topology and electrical component values. Ad-hoc simplifications reduce the models' computational load without affecting perceptual accuracy.

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Conference Paper for the 2nd Pan American/Iberian Meeting on Acoustics, Cancún, Nov. 2010., Nov 2010

Invited paper presented at 2nd Pan American/Iberian Meeting on Acoustics, Cancún, México, Novembe... more Invited paper presented at 2nd Pan American/Iberian Meeting on Acoustics, Cancún, México, November 2010.

ABSTRACT

In 2001, twenty Strombus galeatus marine shell trumpets were excavated at the 3,000 year-old ceremonial center at Chavín de Huántar, Perú, marking the first documented contextual discovery of intact sound-producing instruments at this Formative Period site in the Andean highlands. These playable shells are decorated and crafted for musical use with well-formed mouthpieces created by cutting the small end (spire) off and grinding/polishing the resulting opening. The shells are use-polished, and additionally modified with a v-shaped cut to the outer apical lip. We present an acoustic analysis of the measured response of each instrument, to a variety of excitations, at microphones placed in the mouthpiece, player's mouth, bore, bell, and surrounding near-field. From these measurements we characterize each instrument's sounding frequencies (fundamental and 1st overtone where possible), radiation pattern, and impedance, and we estimate the bore area function of each shell. Knowledge of the specific acoustic capabilities of these pututus allows us to understand and test their potential as sound sources in the ancient Chavín context, whose architectural acoustics are simultaneously studied by our research group.

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Journal of The Acoustical Society of America [Abstract], 2008

Invited paper presented at Acoustics '08, Paris, France, July 2008. ABSTRACT Chavín de Huán... more Invited paper presented at Acoustics '08, Paris, France, July 2008.

ABSTRACT

Chavín de Huántar is a monumental World Heritage archaeological site in the Peruvian highlands, predating Inca society by over 2000 years. The importance of site acoustics is suggested by distinctive architectural features, notably an extensive network of underground galleries used in part for ritual purposes. The labyrinthine galleries are stone-walled and arranged in a series of small rectangular alcoves off narrow corridors. In this work, we initiate research that seeks to understand how the acoustics at Chavín may have influenced auditory experience.

Acoustic measurements and models of a site can be used to archive site acoustics, estimate the acoustics of inaccessible or alternative site architectures, and reconstruct the acoustics of modified or damaged sectors; they may also corroborate aspects of rituals suggested by other archaeological data. Preliminary measurements at Chavín show a short reverberation time, dense and energetic early reflections, and low inter-aural cross correlation. The short reverberation time would enable rhythmically articulated playing of Strombus shell trumpets found on site. The early reflection patterns would provide strong acoustic reinforcement and resonances in gallery alcoves. The wide soundfields would provide a sense of spaciousness and envelopment, contributing to ritual experience.

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Conference Paper presented at Acoustics'08 Paris, 2008

Invited paper presented at Acoustics '08, Paris, France, July 2008. ABSTRACT Chavín de Huán... more Invited paper presented at Acoustics '08, Paris, France, July 2008.

ABSTRACT

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Research presented at the Audio Engineering Society 133rd Convention, San Francisco, CA, 26-29 Oc... more Research presented at the Audio Engineering Society 133rd Convention, San Francisco, CA, 26-29 October 2012.

ABSTRACT

We present a computational acoustic model of the well-preserved interior architecture at the 3,000-year-old Andean ceremonial center Chavín de Huántar, Perú. Our previous model prototype [Kolar et al. 2010] translated the acoustically coupled topology of Chavín gallery forms to a model based on digital waveguides (bi-directional by definition), representing passageways, connected through reverberant scattering junctions, representing the larger room-like areas. Our new approach treats all architectural units as "reverberant" digital waveguides, with scattering junctions at the discrete planes defining the unit boundaries. In this extensible and efficient lumped-element model, we combine architectural dimensional and material data with sparsely measured impulse responses to simulate multiple and circulating arrival paths between sound sources and listeners.

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Journal of The Acoustical Society of America [Abstract], Nov 2010

First Place, Best Student Paper Award in Architectural Acoustics

ABSTRACT

Inspired by on-site observations and measurements, a computational acoustic model of the interior architecture of the 3,000 year-old ceremonial center at Chavín de Huántar, Perú is presented. The model addresses the foundational study by Lumbreras, González and Lietaer (1976) which posited an acoustic system integral to Chavín architecture involving "a network of resonance rooms connected by sound transmission tubes". We propose a translation of the topology of Chavín gallery forms to a modular computational acoustic model based on bi-directional digital waveguides, representing the corridors and ducts, connected through reverberant scattering junctions, representing the small rooms. This approach combines known architectural dimensional and material data with representative measured acoustic data, thus economizing the collection of impulse response measurements required to accurately simulate site acoustics. Applications include virtual acoustic reconstruction of inaccessible or demolished site structures, and auralizations of hypothesized architectural forms, allowing any desired sound sample to be "played back" in the modeled acoustic context.

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