Tim Ziemer

Complex point source model to calculate the sound field radiated from musical instruments

A simple method is described to record the radiated sound of musical instruments and to extrapolate the sound field to distances further away from the source. This is achieved by considering instruments as complex point sources. It is demonstrated that this simplification method yields plausible results not only for small instruments like the shakuhachi but also for larger instruments such as the double bass: The amplitude decays in a given manner and calculated interaural signal differences reaching the listener decrease with increasing distance to the source. The method is applied to analyze the sound radiation characteristics as well as the radiated sound field in a listening region regardless of room acoustical influences. Furthermore, it has been implemented in a psychoacoustic wave field synthesis system to generate the impression of a certain source width. Implementations in terms of room acoustical simulations, spatial additive synthesis and sound field synthesis are discussed.

Wave Field Synthesis

Wave field synthesis enables acoustic control in a listening area by systematic regulation of loudspeaker signals on its boundary. This chapter starts with an overview including the history of wave field synthesis and some exemplary installations. Next, the theoretic fundamentals of wave field synthesis are detailed. Technical implementations demand drastic simplifications of the theoretical core, which come along with restrictions of the acoustic control as well as with synthesis errors. Simplifications, resulting synthesis errors as well as the working principles of compensation methods and their effects on the wave field are extensively discussed. Finally, the current state of research and development is addressed.

Perceptual sound field synthesis concept for music presentation

A perceptual sound field synthesis approach for music is presented. Its signal processing implements critical bands, the precedence effect and integration times of the auditory system by technical means, as well as the radiation characteristics of musical instruments. Furthermore, interaural coherence, masking and auditory scene analysis principles are considered. As a result, the conceptualized sound field synthesis system creates a natural, spatial sound impression for listeners in extended listening area, even with a low number of loudspeakers. A novel technique, the “precedence fade”, as well as the interaural cues provided by the sound field synthesis approach, allow for a precise and robust localization.Simulations and a listening test provide a proof of concept. The method is particularly robust for signals with impulsive attacks and long quasi-stationary phases, as in the case of many instrumental sounds. It is compatible with many loudspeaker setups, such as 5.1 to 22.2, ambisonics systems and loudspeaker arrays for wave front synthesis. The perceptual sound field synthesis approach is an alternative to physically centered wave field synthesis concepts and conventional, perceptually motivated stereophonic sound and benefits from both paradigms.A perceptual sound field synthesis approach for music is presented. Its signal processing implements critical bands, the precedence effect and integration times of the auditory system by technical means, as well as the radiation characteristics of musical instruments. Furthermore, interaural coherence, masking and auditory scene analysis principles are considered. As a result, the conceptualized sound field synthesis system creates a natural, spatial sound impression for listeners in extended listening area, even with a low number of loudspeakers. A novel technique, the “precedence fade”, as well as the interaural cues provided by the sound field synthesis approach, allow for a precise and robust localization.Simulations and a listening test provide a proof of concept. The method is particularly robust for signals with impulsive attacks and long quasi-stationary phases, as in the case of many instrumental sounds. It is compatible with many loudspeaker setups, such as 5.1 to 22.2, ambisonics systems and lo...

Source Width in Music Production. Methods in Stereo, Ambisonics, and Wave Field Synthesis

Source width of musical instruments, measured in degrees, is a matter of source extent and the distance of the observer. In contrast to that, perceived source width is a matter of psychological organization of sound. It is influenced by the sound radiation characteristics of the source and by the room acoustics and restricted by masking and by localization accuracy. In this chapter perceived source width in psychoacoustics and apparent source width in room acoustical research are revisited. Source width in music recording and production practice in stereo and surround as well as in ambisonics and wave field synthesis are addressed. After the review of the literature an investigation is introduced. The radiation characteristics of 10 musical instruments are measured at 128 angles and the radiated sound is propagated to potential listening positions at 3 different distances. Here, monaural and binaural sound quantities are calculated. By means of multiple linear regression, the physical source extent is predicted by sound field quantities. The combination of weighted interaural phase differences in the sensitive frequency region together with the number of partials in the quasi-stationary part of instrumental sounds shows significant correlation with the actual source extent of musical instruments. The results indicate that these parameters might have a relevant effect on perceived source extent as well. Consequently, acoustic control over these parameters will increase psychoacoustic control concerning perceived source extent in audio systems.

Perceptually motivated sound field synthesis for music presentation

The conceptualization and implementation of a psychoacoustic sound field synthesis system for music is presented. Critical bands, the precedence effect, and integration times of the auditory system as well as the radiation characteristics of musical instruments are implemented in the signal processing. Interaural coherence, masking and auditory scene analysis principles are considered as well. The sound field synthesis system creates a natural, spatial sound impression and precise source localization for listeners in extended listening area, even with a low number of loudspeakers. Simulations and a listening test provide a proof of concept. The method is particularly robust for signals with impulsive attacks and quasi-stationary phases as in the case of many instrumental sounds. It is compatible with many loudspeaker setups, such as 5.1, ambisonics systems and loudspeaker arrays for wave front synthesis. The psychoacoustic sound field synthesis approach is an alternative to physically centered wave field ...

Psychoacoustic sonification for tracked medical instrument guidance

In image-guided surgery, displays show a tracked instrument relative to a patients anatomy. This helps the surgeon to follow a predefined path with a scalpel or to avoid risk structures. A psychoacoustically motivated sonification design is presented to help assist surgeons in navigating a tracked instrument to a target location in two-dimensional space. This is achieved by mapping spatial dimensions to audio parameters that affect the magnitude of different perceptual sound qualities. Horizontal distance and direction are mapped to glissando speed and direction of a Shepard tone. The vertical dimension is divided into two regions. Below the target, the vertical distance controls the LFO speed of an amplitude modulation to create a regular beating well below the threshold of roughness sensation. Above the target elevation, the vertical deflection controls the depth of frequency modulation to gradually increase the number and amplitudes of sidebands, affecting perceived noisiness and roughness. This redun...

Perception of a virtual violin radiation in a wave field synthesis system

A method to synthesize the sound radiation characteristics of musical instruments in a wave front synthesis system is proposed and tested. Radiation patterns of a violin are measured with a circular microphone array which consists of 128 pressure receivers. For each critical frequency band one exemplary radiation pattern is decomposed to circular harmonics of order 0 to 64. So the radiation characteristic of the violin is represented by 25 complex radiation patterns. On the reproduction side, these circular harmonics are approximated by 128 densely spaced monopoles by means of 128 broadband impulses. An anechoic violin recording is convolved with these impulses, yielding 128 filtered versions of the recording. These are then synthesized as 128 monopole sources in a wave front synthesis system and compared to a virtual monopole playing the unfiltered recording. The subjects perceive the tone color of the recreated virtual violin as being dependent on the listening position and report that the two source ty...

Perceptual evaluation of violin radiation characteristics in a wave field synthesis system

A method to synthesize the sound radiation characteristics of musical instruments in a wave field synthesis (WFS) system is proposed and tested. Radiation patterns of a violin are measured with a circular microphone array which consists of 128 pressure receivers. For each critical frequency band one exemplary radiation pattern is decomposed to circular harmonics of order 0 to 64. So the radiation characteristic of the violin is represented by 25 complex radiation patterns. On the reproduction side, these circular harmonics are approximated by 128 densely spaced monopoles by means of 128 broadband impulses. An anechoic violin recording is convolved with these impulses, yielding 128 filtered versions of the recording. These are then synthesized as 128 monopole sources in a WFS system and compared to a virtual monopole playing the unfiltered recording. The study participants perceive the tone color of the recreated virtual violin as being dependent on the listening position and report that the two source typ...

Psychoacoustic sonification design for navigation in surgical interventions

A psychoacoustically motivated sonification design to guide clinicians in two-dimensional space is presented, e.g., to navigate a scalpel towards a target resection trajectory, ablation needle towards a pre-planned insertion point, or drill towards a target burrhole for craniotomy. Navigation is achieved by mapping spatial dimensions to audio synthesis parameters that affect the magnitude of different perceptual sound qualities. Orthogonal spatial dimensions are mapped to orthogonal auditory qualities.In a preliminary laboratory study, non-expert users successfully identified the target field out of 16 possible fields in 41% of all trials. The correct cardinal direction was identified in 84% of the trials. Based on both findings and further psychoacoustic considerations, the mapping range is optimized, and an implementation of an additional depth dimension is discussed.

Using Psychoacoustic Models for Sound Analysis in Music

Overall sound perception of a song is an important attribute of music. Several psychoacoustic models have been studied to extract perceptual sound qualities from audio signals. By means of listening tests, we investigate whether these sound models successfully reflect (inter-)subjective perception of sound resemblance in music. Preliminary results shows that psychoacoustic descriptors are in better accordance with subjective judgments than low-level features. As the psychoacoustic descriptors model auditory perception, we can assume causal relationships and directly draw conclusions on perception from the listening test results. We observed that roughness is the most crucial sound resemblance criteria, followed by sharpness, loudness, spaciousness and tonalness. The findings indicate that these psychoacoustic models may be suitable for music data mining, music browsing, automatic playlist generation and music recommendation tasks.