Hi-Fi Digital Audio Compensation System Patrick Cronin Robert Galvin Matt Saterbak Kent Thomson Nick Turner Ryan Twaddle Advisor: Professor Jaijeet Roychowdhury University of Minnesota – Twin Cities Spring 2007

Hi-Fi Audio Compensation System Motivation (Nick) Development of transfer function (Patrick) How we will measure transfer function (Robert) Software/Hardware used (Matt) Possible extensions (Ryan) Schedule (Robert) Budget (Kent) Summary (Kent)

Problem Statement The speakers degrade the quality of sound produced by the computer’s audio output High Fidelity speakers and amplifiers that are able to maintain the sound produced by modestly-priced soundcards are very expensive

Motivation Creates the need for an easy to operate system with quantitative analysis about a Hi-Fi setup We need to identify a transfer function between the sound-card’s output and what is eventually heard by listener taking into account the amplifier, speakers, and room acoustics  Calibrated Microphone  Digital Signal Processing

Hasn’t anyone done this before? High-end speakers do exist which have audio characterization and enhancement capabilities  Overly Expensive  Correction indiscernible Our solution is software based  Open-source & will work with any set of speakers  Plug-in to offer better sound optimization without the cost of high-end hardware  User only needs: Calibrated Microphone (Known Frequency Response) Computer with soundcard

Sound card amplifier Stereo Amplifier Audio Speakers Room Acoustics Example Transfer Function of Audio Equipment Setup All these components are included in calculating H(s) of system

System Transfer Functions Uncompensated System Frequency Response Compensated System Frequency Response

Microphone Transfer Function TF = MF(s)

Block Diagram

Aliasing Due to the high sampling rate, we can ignore aliasing

Windowing Sending pure sine waves, we can ignore all the noise from other frequencies

End Transfer Function

Obtaining the filter

Hardware/Software Microphone BruteFIR filter ALSA

LinearX Calibrated Microphone

BruteFIR: Finite Impulse Response filter library Written in C – Allows Linux optimization Partially hand assembled for maximum efficiency on Intel architecture Includes Hamming windowing capability

Latest standard for sound in Linux Built-in to all recent Linux kernels Allows easy interfacing between Operating System and most soundcards Allows expansion with plugins Will allow binary packaging for multiple Linux- based operating systems

Possible Extensions Add a graphical user interface to the program to enhance its usability, and allow for less experienced Linux users to operate the software

Possible Extensions (cont.) Along with measuring the transfer function of the speakers, the limits of tolerance of the speakers could also be measured. With these measurements the filter can be adjusted to these limits.

Possible Extensions (cont.) Include in the filter design a setting for very large rooms. The filter can compensate for excessive amounts of echoes that the room presents.

Project Continuations Develop a technique to get the desired frequency response for a much wider area. This would prevent someone from moving out of the “sweet spot” and hearing poor sound quality.

Project Continuations (cont.) A study of how well the techniques used to develop the program works. Can these techniques be applied to superior quality speakers?

Project Continuations (cont.) The program could model the room in which the speakers are located using a general rectangular model.

And Finally… One aspect of speaker quality that has so far been left out is attack and decay time. Sending certain frequencies to the speaker with slight delays may result in a better sound.

Advisor PresentationsJanuary-07 First Team MeetingJanuary-07 Brute Fir filter - able to be constructedFebruary-07 Output sound on computerFebruary-07 Design ProposalFebruary-07 Design Review PresentationFebruary-07 Microphone inFebruary-07 Speakers inFebruary-07 Matlab on ComputerFebruary-07 Sound file for output obtainedFebruary-07 Transfer curve of speakers obtainedMarch-07 Brute Fir filter - as actual filter (H(s) inverse)March-07 GUI obtainedApril-07 program is able to find the transfer function of a system on it ownApril-07 Executive Summary - prepApril-07 Final Project complete to specsApril-07 Executive Summary - draftApril-07 Product Launch PresentationApril-07 Executive SummaryMay-07 Poster Session/Product DemoMay-07 Final Report May-07

Projected Budget ItemPrice LinearX M31 Calibration Microphone and Clip$190 Adapter Cables$10 Microphone Stand$25 9V Batteries$20 Total$245

Quick Summary Poor quality speakers can sound better with proper equalization A calibrated microphone can measure the deficiencies in the frequency response of the speakers A software program can apply an equalization to make up for the speaker’s imperfections

Conclusion A speaker correction system for Linux can be developed using ALSA and a calibration microphone