Musical Acoustics Lab

History

The Laboratory is based in the Palazzo dell’Arte, the prestigious location of the Museo del Violino, in Cremona. It was created in 2013 thanks to the competencies of the Image and Sound Processing Group (ISPG) of the Dipartimento di Elettronica, Informazione e Bioingegneria (Deib) of Politecnico di Milano with the collaboration of the Dipartimento di Meccanica and financed by the Arvedi Buschini and Cariplo Fundations (as part of the Distretto culturale della provincia di Cremona project). The Laboratory collaborates and shares spaces and equipments with the Arvedi Laboratory of non-invasive Diagnostics of the Università degli Studi di Pavia. The Acoustics Lab reaps the experience in audio, acoustic computing and machine intelligence fields of the ISPG group and the competencies of the Dipartimento di Meccanica in vibro-acoustic analysis, aiming at improving the quality of musical instruments (with particular attention to classical and contemporary violin making products) and of listening spaces.

Goals

The Acoustics Lab follows two main goals: first, to develop a multidisciplinary research for the improvement of the Cremona violin-making tradition and second, to enhance its cultural value. To support violin making, the main research activities concern:

• the physical and acoustic properties of the instrument, namely the vibratory and timbral analysis, 3D modeling;
• the radiating properties and the interaction capacity with the surroundings, and specifically the study and development of measurement and project solutions in order to estimate and control the acoustic emission characteristics, with particular attention to the radiative projection of the instrument.

In order to enhance the violin making culture, the principal activities focus on the development of effective and innovative solutions for the “spatial audio” recording and playing. These technologies enable to catch acoustic scenes in a “holographic” way and re-experience them as if still immersed in those scenes. The research refers mostly to:

• Olophonic data capture techniques, based on microphones arrays and acoustic chambers;
• “Spatial-audio” data capture techniques based on higher order microphones (eigenmikes, cylindrical/spherical arrays).

Equipment and Spaces

• Rendering room: 8x5mt semi-anechoic vibro-acoustic insulated room, used for acoustic and timbral recordings/measurement and for spatial audio acoustic performance tests. The room hosts an Ambisonic rendering system with 17 high performance speakers and a data-capture system with 64 microphones for olophonic recordings.
• Vibrational analysis and 3D modeling laboratory: multifunctional lab equipped with the adequate instruments to acquire high resolution 3D models of musical instruments, to model the vibrational behavior and to estimate the radiating performance. The laboratory has a laser scanner, a wide range of calibrated acceletometric sensors and a laser-interferometry vibrometer for non-invasive diagnostics.
• Control room: mobile equipment for the high quality/resolution recording of live events in spatial audio. In addition to mixing systems and professional microphones the laboratory owns an Eigenmike for the control of virtual microphones and the audio recording in Ambisonic mode.
• Open Space/office: room equipped with several workstations dedicated to software development.

In addition to the equipment listed above, other facilities of the Acoustics Lab are:

• Mobile system for multichannel audio recordings and spatial audio made of an array of AD/DA (64 full-duplex channels, 192kHz, 24 bit) converters with high performance preamplifiers.
• 64 microphones measurement system;
• Step-by-step handling system controlled by a PC, for the automatic positioning of the microphones and loudspeakers array (Head-Related Transfer Function measurements, radiance pattern measurements, noise, absorption, etc.)
• Array of loudspeakers for the plenacoustic/olophonic rendering, with related multichannel amplifiers, for the measurement of HRTF and controlled acoustic fields.

Activities

Vibrometric Analysis

Focused on the vibrational modeling of the violin, it bases on vibrational measurements and FEM finite elements simulations. The model can be used to infer the vibrational behavior of historical and contemporary instruments, and to estimate the acoustic projection (radiance) of the instrument.

Acoustic radiance analysis

Study of the distribution of the acoustic energy in all directions. High resolution, non-invasive methods are used to analyze the radiance during a performance: plenacoustic cameras and specific devices are employed to track the position of the musical instrument in the space (gyroscopes and Microsoft Kinect).

Timbral analysis

Study of the relation between the objective sound features and the high level timbral description related to human perception, by means of machine intelligence techniques. Development of new methods for timbral analysis of the violins. Analysis are performed on the recordings acquired in an anechoic chamber by means of professional measurement microphones.

3D audio recording and rendering

Development of techniques for music production in spatial audio. The acquisition is made by an 32 capsules Eigenmike and reproduced on an Ambisonic rendering system with 17 speakers.

 

Violin making ontology and applications

Development of an ontology related to the violin making knowledge, from materials to timbral descriptors (in collaboration with the Arvedi Laboratory for Non-invasive Diagnostics). Applications to the automatic timbral description and semantic browsing.

Acoustic and environmental measurements

Development and implementation of an acoustic modeling system and of an environment characterization protocol (Arvedi Auditorium’s mapping).

 

Scientific Repository

The great variety and amount of data acquired by the two Laboratories required the set up of a system able to easy access and manage them. For this reason a data base was designed and implemented on a Network Attached Storage (NAS), which can be only accessed by the Labs’ internal network. Thanks to this database it is possible to store and manage images, audio recordings, 3D scans, vibrometric measurements, and any other information retrieved from studies carried on by the two universities. As far as the Musical Acoustics Laboratory is concerned, the current database includes audio recordings of more than 30 (historical and modern) violins, acquired following a specific protocol and performed by a professional violin player.