Emanuele Ugolotti

Non-linear Digital Audio Processor For Dedicated Loudspeaker Systems

A non-linear loudspeaker model, which accurately reproduces the low frequency behavior, is presented. This description, derived from an extension of the well known Small-Thiele (1972) equations, requires far less computational time and memory space than generic non-linear structures. Moreover a noticeable further reduction of the number of operations and of the memory cells required has been achieved by means of a multirate architecture. Inversion of the proposed model allows digital prefiltering of the electrical signal in order to compensate for the non-idealities of the electroacoustic conversion. The above filter structure implemented on a digital signal processor, placed between the audio signal source and the power amplifier allows effective compensation of loudspeaker linear (both magnitude and phase) and non-linear distortion. Measurement results obtained with a commercial woofer are discussed.

Car cockpit equalization by warping filters

Sound reproduction within a car inside is a difficult task. Reverberation, reflection, echo, noise and vibration are some of the issues to account for. A first step in the direction of increasing sound comfort is that of equalizing the acoustic pressure response in the frequency domain. A direct solution is that of implementing with a convolution filter the inverse of the acoustic measurements in the car cockpit. However this often results in very high number of taps, therefore more complex techniques must be adopted, which rely also on psychoacoustics considerations. In this paper automatic tools to develop warping inverse filters for target car cockpits was designed and validated through experiments in commercial cars.

Design of a DSP-based 24 bit digital audio equalizer for automotive applications

The project deals with the design and realization of a dedicated board DSP-based for the processing of audio signals for automotive applications (DIGIcar). The I/O interface of the board is composed of two stereo inputs and two stereo outputs. The prototype was realized in a four layer PCB with SMD components. The layers were designed in order to reduce high frequency effects of digital signals on analog audio signals. The DIGIcar board was tested stand-alone with an Audio Precision System 2022. Experiments were performed inside a car too, where the DIGIcar board was interfaced with a four channel power amplifier and connected between audio source and car loudspeakers. A development tool in MATLAB was exploited to synthesize the suitable equalizing filters given standard car acoustic measurements. Then the filters are stored in the board flash EEPROM. A few options are available to tailor the equalizer for different cars. Listening tests and acoustic measurements show the effectiveness and the functionality of the designed board.

Experimental validation of warping filters inside car cockpits

Sound reproduction within a car inside is a difficult task. Reverberation, reflection, echo, noise and vibration are some of the issues to account for. A first step in the direction of increasing sound comfort is that of equalizing the acoustic pressure response in the frequency domain. A direct solution is that of implementing with a convolution filter the inverse of the acoustic measurements in the car cockpit. However this often results in very high number of taps, therefore more complex techniques must be adopted, which rely also on psychoacoustic considerations. An automatic tools to develop warping inverse filters for target car cockpits was designed and validated through experiments in commercial cars.