Oscar A. Ramos

Human echolocation: The ECOTEST system

Abstract The ECOTEST (EChOlocation TEST) is one of the modules of a PC based system — Rousettus — developed in order to study the human echolocation process, i.e. the ability for auditive perception of obstacles without the use of vision. The ECOTEST allows, rapidly and in a flexible way, the construction and management of specially designed auditive perception tests in order to analyse the psychoacoustic aspects of echolocation. Efficient construction of the tests, using real or artificial echolocation signals as sound stimuli, was achieved through the implementation of a specific computational language. The results, which are based on an experiment carried out with 30 sighted subjects and one blind person, indicated that the ECOTEST is a potentially valuable tool for the evaluation, prediction and training of the echolocation ability by the visually handicapped person through auditive perception tests .

Spatial Hearing in Reverberant Environments: Main Theoretical Aspects

In recent years there has been a growing interest in the study of listener’s abilities to function in reverberant spaces where a sound propagates in multiple directions and is reflected from nearby surfaces. This article deals with theoretical considerations of spatial audition in the presence of reflections, in particular with the precedence effect. It is considered as a strategy that listeners unconsciously employ to cope with multiple arrays of directional cues in reverberant spaces. It refers to the auditory phenomenon that occurs when two similar sounds are presented from different locations with a brief delay between them and only one sound is heard whose perceived location is dominated by the first arriving sound.

SAMSoft: Acoustical devices automatic measurement system software

A common way to experimentally characterize a linear time-invariant acoustic system is by measuring its impulse response for each location of interest. Currently several methods exist for such purpose, signal deconvolution being the one which exhibits best performance. Moreover, measurement systems are usually aimed to particular applications, working with expensive platforms and proprietary software. This paper describes design and development of specific software, which manages an automatic measurement system for acoustic devices. SAMSoft presents a modular, scalable and easy to upgrade design developed in MATLab, based on the model-view-control system pattern which enables source code reuse and facilitates further development. This software allows impulse response measurement with different excitation signals, user-selected processing intervals, time and frequency domain visualization, and spectral analysis in octave and one-third octave bands. It runs on hardware consisting of a control unit and a mobile platform, and is capable of measuring 360° in the horizontal plane with an angular resolution of up to 0.06°. Impulse responses measured from different acoustic transducers showed a signal noise ratio of up to 40 dB in frequency bands under 100 Hz. In power measurements for octave and one-third octave bands a maximum error of 0.12 dB was obtained.A common way to experimentally characterize a linear time-invariant acoustic system is by measuring its impulse response for each location of interest. Currently several methods exist for such purpose, signal deconvolution being the one which exhibits best performance. Moreover, measurement systems are usually aimed to particular applications, working with expensive platforms and proprietary software. This paper describes design and development of specific software, which manages an automatic measurement system for acoustic devices. SAMSoft presents a modular, scalable and easy to upgrade design developed in MATLab, based on the model-view-control system pattern which enables source code reuse and facilitates further development. This software allows impulse response measurement with different excitation signals, user-selected processing intervals, time and frequency domain visualization, and spectral analysis in octave and one-third octave bands. It runs on hardware consisting of a control unit and a mob...

Speech transmission index variation due to ventilating and air-conditioning system in university classrooms

A major factor to be considered in the study of teaching-learning process based on spoken communication is sound field. Excessive background noise levels or reverberation time values inside a classroom interfere with oral communication, creating an acoustic barrier to the teaching-learning process. In previous work, reverberation time was measured in a sample of university classrooms in the City of Cordoba, observing that such parameter has tripled the value recommended by international literature. Furthermore, background noise level was measured in two different conditions: heating, ventilating and air-conditioning system turned on and off. Then, these levels were evaluated according to NC and RC criteria established by IRAM 4070, where more than 50 % of the population under study complied with the NC criteria, and none with the RC criteria. In this paper, results of speech transmission index (STI) measurements for both conditions of heating, ventilating and air-conditioning system are presented. Results...

Individual head-related impulse response measurement system with 3D scanning of pinnae

Head-related impulse responses (HRIRs) in the time domain, or head-related transfer functions (HRTFs) in the frequency domain, characterize the transmission between a sound source and the eardrums of a subject. They are different for each ear, angle of incidence, and also vary from person to person due to the anatomical differences. Individual measurement of HRIRs become required for applications where precise simulation of the acoustic scene is necessary, such as virtual auditory environments, and for validation of HRTF personalization methods. This presentation describes a HRIR measurement system, which uses as excitation signal logarithmic sine sweep or also binary sequences known as Golay codes. The system also has a 3D scanner mounted over detachable holders that captures the digital models of the pinnae as a mesh. The results of measurements carried out in a head and torso simulator with soft pinnae are presented.