Audio Signal Processing

Audio based Context Awareness on a Pocket PC

by Filip Bonnevier

Obtaining Binaural Room Impulse Responses From B-Format Impulse Responses Using Frequency-Dependent Coherence Matching

by Hervé Lissek

First author: Fritz Menzer. Co-authored with Christof Faller

Measuring binaural room impulse responses (BRIRs) for different rooms and different persons is a costly and... more Measuring binaural room impulse responses (BRIRs) for different rooms and different persons is a costly and time-consuming task. In this paper, we propose a method that allows to compute BRIRs from a B-format room impulse response (B-format RIR) and a set of head-related transfer functions (HRTFs). This enables to measure the room-related properties and head-related properties of BRIRs separately, reducing the amount of measurements necessary for obtaining BRIRs for different rooms and different persons to one B-format RIR measurement per room and one HRTF set per person. The BRIRs are modeled by applying an HRTF to the direct sound part of the B-format RIR and using a linear combination of the reflections part of the B-format RIR. The linear combination is determined such that the spectral and frequency-dependent interaural coherence cues match those of corresponding directly measured BRIRs. A subjective test indicates that the computed BRIRs are perceptually very similar to corresponding directly measured BRIRs.

Audio Synthesis Possibilities on Mobile Devices Using the Apple iPhone and iPad

by Markus Konrad

Paper for our "Independent Coursework" in semester 2 of Media & Computing study course at the HTW Berlin.

This paper covers the topic of real-time audio synthesis on mobile Apple devices like the iPhone or the iPad (iOS... more This paper covers the topic of real-time audio synthesis on mobile Apple devices like the iPhone or the iPad (iOS devices). Such mobile multi-touch devices introduced an interesting new kind of user interaction and user experience. Applying them to the music context, can create an exciting new world of musical instruments.
Unfortunately, only very little information exists until now (March 2011) about audio synthesis on iOS devices. There is only one book that will cover this topic in a few chapters and this book will not be released before August 2011. Therefore I hope that this paper brings some light into the darkness. It analyses existing techniques and libraries for these devices and describes the advantages and disadvantages of the chosen libraries. Short examples of how to use them will be given. Two of the introduced libraries, namely LibPd and Core Audio, will be covered in more detail.
The paper concludes with an overall estimation about the audio synthesis possibilities of iOS devices. The appendix consists of some example applications that implement the mentioned techniques.

Morphology and spoken word comprehension: Electrophysiological investigations of internal compound structure

by Dirk Koester

No 47 of the downloads on this page: http://www.cbs.mpg.de/institute/mpi_series

The present Ph.D. thesis investigated morphosyntactic and lexical-semantic aspects of German compound comprehension.... more The present Ph.D. thesis investigated morphosyntactic and lexical-semantic aspects of German compound comprehension. Previous studies, on one hand, provide inconclusive evidence for semantic decomposition of nominal compounds during acoustic presentation (Isel et al., 2003; Pratarelli, 1995;Wagner, 2003). On the other hand, morphological effects of decomposition have only been investigated in the visual modality which cannot be generalised to the auditory modality (Andrews, 1986; Sandra, 1990; Zwitserlood, 1994). The purpose of the present experiments was to answer the question of whether and how compound constituents are accessed from the mental lexicon during auditory comprehension, i.e. whether or not compounds are decomposed.

Dynamic range control of digital audio signals

by Guy McNally

Movie Summarization based on Audiovisual Saliency Detection

by Georgios Evangelopoulos

A Reduced Multiple Gabor Frame for Local Time Adaptation of the Spectrogram

by Marco Liuni

Rényi information measures for spectral change detection

by Marco Liuni

Sound Analysis and Synthesis Adaptive in Time and Two Frequency Bands

by Marco Liuni

An entropy based method for local time-adaptation of the spectrogram

by Marco Liuni

Optimized Polynomial Spline Basis Function Design for Quasi-Bandlimited Classical Waveform Synthesis

by Jussi Pekonen

(Co-authored with Juhan Nam, Julius O. Smith, and Vesa Välimäki) IEEE Signal Processing Letters, vol. 19, no. 2, pp. 159-162, March 2012.

Classical geometric waveforms used in virtual analog synthesis suffer from aliasing distortion when simple sampling is... more Classical geometric waveforms used in virtual analog synthesis suffer from aliasing distortion when simple sampling is used. An efficient antialiasing technique is based on expressing the aveforms as a filtered sum of time-shifted approximately bandlimited polynomial-spline basis functions. It is shown that by optimizing the coefficients of the basis function so that the aliasing distortion is perceptually minimized, the alias-free bandwidth of classical waveforms can be expanded. With the best of the case examples given here, the generated impulse-train and sawtooth waveform are alias-free up to fundamental frequencies over 10 kHz when the sampling rate is 44.1 kHz.

VOXALEAD: A Scalable Video Search Engine Based On Content

by Gregory Grefenstette

Julien LawTo, Gregory Grefenstette, "VOXALEAD: A Scalable Video Search Engine Based On Content" ACM Multimedia 2011, Technical Demos, Nov 28th - Dec 1st, 2011 Scottsdale, Arizona, USA

Most news organizations provide immediate access to topical news broadcasts through RSS streams or podcasts. Until... more Most news organizations provide immediate access to topical news broadcasts through RSS streams or podcasts. Until recently, applications have not permitted a user to perform content based search within a longer spoken broadcast to find the segment that might interest them. Recent progress in both automatic speech recognition (ASR) and natural language processing (NLP) has produced robust tools that allow us to now provide users with quicker and more focused access to relevant segments of news broadcast videos. Our public online demonstrator of the Voxalead application currently indexes daily broadcast news content from 50 sources in English, French, Chinese, Arabic, Spanish, Dutch, Italian and Russian.

Perceptually Informed Synthesis of Bandlimited Classical Waveforms Using Integrated Polynomial Interpolation

by Jussi Pekonen

(Co-authored with Vesa Välimäki and Juhan Nam) Journal of the Acoustical Society of America, vol. 131, no. 1, pp. 974-986, January 2012. Special issue on Musical Acoustics.

Digital subtractive synthesis is a popular music synthesis method, which requires oscillators that are aliasing-free... more Digital subtractive synthesis is a popular music synthesis method, which requires oscillators that are aliasing-free in a perceptual sense. It is a research challenge to find computationally efficient waveform generation algorithms that produce similar-sounding signals to analog music synthesizers but which are free from audible aliasing. A technique for approximately bandlimited waveform generation is considered that is based on a polynomial correction function, which is defined as the difference of a non-bandlimited step function and a polynomial approximation of the ideal bandlimited step function. It is shown that the ideal bandlimited step function is equivalent to the sine integral, and that integrated polynomial interpolation methods can successfully approximate it. Integrated Lagrange interpolation and B-spline basis functions are considered for polynomial approximation. The polynomial correction function can be added onto samples around each discontinuity in a non-bandlimited waveform to suppress aliasing. Comparison against previously known methods shows that the proposed technique yields the best tradeoff between computational cost and sound quality. The superior method amongst those considered in this study is the integrated third-order B-spline correction function, which offers perceptually aliasing-free sawtooth emulation up to the fundamental frequency of 7.8 kHz at the sample rate of 44.1 kHz.

Speech event detection using multiband modulation energy

by Georgios Evangelopoulos

Advances on calculating effective dither for audio signals

by Andreas Floros

A. Floros and M. Avlonitis, “Advances on Calculating Effective Dither for Audio Signals”, Proceedings of the 10th International Conference on SYSTEMS, July 10 – 12 2006, Athens, Greece, pp. 614 – 618.

Dithering represents a well-established, attractive technique for minimizing the audibility of the error produced... more Dithering represents a well-established, attractive technique for minimizing the audibility of the error produced during requantization of digital audio signals. However, it is also known that, as dither is applied as controlled, additive random noise prior requantisation, it also increases the overall quantization noise level and audibility. In this work, a novel dither generator is presented, based on a novel stochastic approach that derives a statistically equivalent signal to the original input. Using a sequence of tests as well as objective and psychoacoustic measurements, it is shown that the addition of the proposed dither generator output to the initial input signal and the application of a low-order noise shaper significantly suppresses the quantization error perception.

Computationally Efficient Hammond Organ Synthesis

by Jussi Pekonen

(Co-authored with Tapani Pihlajamäki and Vesa Välimäki) in Proceedings of the 14th International Conference on Digital Audio Effects (DAFx-11), Paris, France, pp. 19-23, September 19–23, 2011.

The Hammond organ is an early electronic musical instrument, which was popular in the 1960s and 1970s. This paper... more The Hammond organ is an early electronic musical instrument, which was popular in the 1960s and 1970s. This paper proposes computationally efficient models for the Hammond organ and its rotating speaker system, the Leslie. Organ tones are generated using additive synthesis with appropriate features, such as a typical fast attack and decay envelope for the weighted sum of the harmonics and a small amplitude modulation simulating the construction inaccuracies of tone wheels. The key click is realized by adding the sixth harmonic modulated by an additional envelope to the original organ tone. For the Leslie speaker modeling we propose a new approach, which is based on time-varying spectral delay filters producing the Doppler effect. The resulting virtual organ, which is conceptually easy, has a pleasing sound and is computationally efficient to implement.

The Brief History of Virtual Analog Synthesis

by Jussi Pekonen

(Co-authored with Vesa Välimäki) in Proceedings of the 6th Forum Acusticum, Aalborg, Denmark, pp. 461-466, European Acoustics Associations, June 26 - July 1, 2011.

In the 1960s and 1970s, most electrical (or analog) synthesizers were based on a sound synthesis technique called... more In the 1960s and 1970s, most electrical (or analog) synthesizers were based on a sound synthesis technique called subtractive synthesis, in which a spectrally rich source signal, typically a sawtooth or rectangular pulse wave, is filtered with a time-varying filter. In the 1980s and 1990s this synthesis technique was almost overtaken by other synthesis techniques but in the mid-1990s musicians started again to show interest in the ''warm`` sound of subtractive synthesis. To meet this interest, a Swedish company Clavia introduced in 1995 the NordLead synthesizer that used the subtractive sound synthesis but in digital domain. Furthermore, they introduced the term ''virtual analog`` to represent the digital simulation of the analog audio devices. Since then research on digital signal processing methods for subtractive sound synthesis has increased and more and more interest has been shown to the topic in the past few years. In fact, the last year (2010) was again record-breaking when the number of publication on this topic is considered. In this paper, the history of the publications of virtual analog synthesis research is reviewed. In addition to the publication count over the years, the viewpoints of this paper include the distribution of the methodologies presented in the publications.

Discrete-Time Modelling of the Moog Sawtooth Oscillator Waveform

by Jussi Pekonen

(Co-authored with Victor Lazzarini, Joseph Timoney, Jari Kleimola, and Vesa Välimäki) EURASIP Journal on Advances in Signal Processing, vol. 2011, Article ID 785103, 15 pages, 2011. Special issue on Musical Applications of Real-Time Signal Processing.

Discrete-time modelling strategies of analogue Moog sawtooth oscillator waveforms are presented. Two alternative... more Discrete-time modelling strategies of analogue Moog sawtooth oscillator waveforms are presented. Two alternative approaches suitable for real-time implementation are proposed, one modelling the analogue waveform in time-domain using phase distortion synthesis and another matching the spectrum of an existing antialiasing sawtooth oscillator to the corresponding analogue spectrum using a first-order IIR post-equalising filter. A parameter estimation procedure for both approaches is explained and performed. Performance evaluation using polynomial fits for the estimated parameters is carried out and good matches between the model outputs and recorded waveforms are obtained. The best match of the tested algorithms is produced by the phase distortion model and by post-equalising the fourth-order B-spline bandlimited step function sawtooth oscillator.

Digital Emulation of Distortion Effects by Wave and Phase Shaping Methods

by Jussi Pekonen

(Co-authored with Joseph Timoney, Victor Lazzarini, and Anthony Gibney) in Proceedings of the 13th International Conference on Digital Audio Effects (DAFx-10) (Hannes Pomberger, Franz Zotter and Alois Sontacchi, editors), Graz, Austria, pp. 419-422, September 6-10, 2010.

This paper will consider wave (amplitude) and phase signal shaping techniques for the digital emulation of distortion... more This paper will consider wave (amplitude) and phase signal shaping techniques for the digital emulation of distortion effect processing. We examine how to determine the Wave- and Phase-shaping functions with harmonic amplitude and phase data. Three distortion effects units are used to provide test data. The action of the Wave- and Phase-shaping functions derived for these effects is demonstrated with the assistance of a super-resolution frequency-domain analysis technique.

On Minimizing the Look-Up Table Size in Quasi-Bandlimited Classical Waveform Oscillators

by Jussi Pekonen

(Co-authored with Juhan Nam, Julius O. Smith, Jonathan S. Abel, and Vesa Välimäki) in Proceedings of the 13th International Conference on Digital Audio Effects (DAFx-10) (Hannes Pomberger, Franz Zotter and Alois Sontacchi, editors), pp. 57-64, Graz, Austria, September 6-10, 2010.

In quasi-bandlimited classical waveform oscillators, the aliasing distortion present in a trivially sampled waveform... more In quasi-bandlimited classical waveform oscillators, the aliasing distortion present in a trivially sampled waveform can be reduced in the digital domain by applying a tabulated correction function. This paper presents an approach that applies the correction function in the differentiated domain by synthesizing a bandlimited impulse train (BLIT) that is integrated to obtain the desired bandlimited waveform. The ideal correction function of the BLIT method is infinitely long and in practice needs to be windowed. In order to obtain a good alias-reduction performance, long tables are typically required. It is shown that when a short look-up table is used, a windowed ideal correction function does not provide the best performance in terms of minimizing aliasing audibility. Instead, audibly improved alias-reduction performance can be obtained using a look-up table that has a parametric control over the low-order generations of aliasing. Some practical parametric look-up table designs are discussed in this paper, and their use and alias-reduction performance are exemplified. The look-up table designs discussed in this paper providing the best alias-reduction performance are parametric window functions and least-squares optimized multi-band FIR filter designs.