Project description                                                                                

3.1 Sound Imaging Tool  

3.2 Project objectives  

3.3 Implementation  

3.4 Activities and schedule  

Chapter 3: Project description

3.1 Sound Imaging Tool

In theater system or home surround system, there are some tools being developed for professionals to setup and check the system for correct imaging.  The listening environment can creates distortions caused by multi-paths of acoustic sound and other causes.  These can cause imaging, or sound localization errors, to the listener.  One such product is called the LEDR [4]� Listening Environment Diagnostic Recoding � tool.  The LEDR is an objective tool for testing and adjusting loudspeakers, and room acoustics that requires no test instrumentation. If a stereo system corrupts or distorts one or more of the LEDR paths, that system cannot be considered accurate. 

The LEDR consists of a series of computer-generated sounds that are intended to move in a predefined way between a pair of loudspeakers. A sampled instrument music is electronically manipulated to move through three different paths. The paths are Up, Over, and Lateral. The differences between what these signals are designed to do, and what the test system actually produce, represent a measure of the imaging accuracy of the stereo speakers, electronics, and the room environment.

The first path - Up path.  This path is generated first in the left speaker, then in the right. The sound should begin at about eye level and then travel as straight as possible up in the air about 6'.

The second path - Over path, also called the "Rainbow" path. The sound begins at one speaker and travel in a smooth arc to the other speaker, from left to right and then returning. The top of the rainbow should be as high as the previous Up signal (about 6' above eye level).

The last path - Lateral, tests left-to-right stereo imaging. This consists of four elements.

First, the sound moves from left to right, between the acoustic centers of the speakers. Since a speaker's acoustic center may not be its physical center, the first Lateral test is used to adjust your speakers until the sound traverses a 60 degrees angle from the listener's point of view.

Second, the sound moves from beyond the right loudspeaker to beyond the left (about 1' out from acoustic center).

The next two signals are the mirror image of the above; Third, from right to left speaker; and Fourth, from beyond the left to beyond the right.

The LEDR test can be use to grade the test system by how straight, continuous, and symmetrical the paths are.

3.2 Project objectives

The project objective is to develop a tool for testing and grading a four speakers home surround system � two front and two rear speakers � by moving a sound laterally at fix positions around the listener. Refer to figure 3.1.  These will not only demonstrate the localization cues, but also provide a simple tool for grading and improving the speaker locations / settings, and to check the listening environment.

As an extended goal after achieving the main objective, frequency notches may be introduces to simulate sound localization in the vertical plane from the front center to the rear center.

           Figure 3.1: Speaker�s layout and simulated sound locations

3.3 Implementation

Below are the implementation processes for realizing the objective.

The DSP board in mind is the Speedy33.  As only two channels are available on each board, it is proposed to have two such DSP boards to process the codes, and feed to the front and rear power amplifiers for driving the four speakers.  Refer to figure 3.2.

Figure 3.2: Hardware block diagram

The two dual channels power amplifiers shall be fabricated based on an off-the-shelve design.

Four 5-Watts loudspeakers shall be acquired.

A program using Matlab will be written to condition a music sound wave file in magnitude, phase and frequency in each of the four channels to simulate direction of the sound as in figure 3.1 above.

Labview shall be used to program the codes to the two Speedy33 boards.

Extended goal:

After achieving the basic objective above, frequency notches may be introduces to the codes to simulate the sound source in the vertical plane.

3.4 Activities and schedule:

Month             Task / Deliverables

May 07             Code writing and simulation.

Jun /Jul 07         Fabricate amplifiers and setup test configuration.

Acquire loudspeakers.

                        Test program.

                        Extended goal � localization in median plane.

                        Preparation of FYP Final report.

Aug 07              Preparation of website.

                        Presentation material.