IPRO 344 Fall 2009
In the Fall 2009 IPRO 344 is continuing a project that has started 4 semesters ago. The original project was based on a research into mobile amplifiers and later evolved into this semester's task: collecting data and improving upon a 2-way intercom system that utilizes class D amplifiers. Last semester a second prototype of a drive-thru system was successfully developed. This semester we hope to analyze the quality of this system, collect pertinent and consistent data and make adjustments to improve audio quality.

click image for the full system diagram

Testing and Collecting Data
As a part of the testing methodology a wide set of real life scenarios will be introduced. In addition to the spacial features of the setup (relative position to the kiosk) relevant sound situations with variable frequency characteristics and noise levels will help improve the data obtained from testing. These sound instances can be recorded and then monitored for variability using the TrueRTA software.
The testing main criteria is the Speech Transmision Index (STI) which is a measure of speecch inteligibility. STI values varies from 0 = completely unintelligible to 1 = perfect intelligibility. On this scale, an STI of at least .5 is desirable for most applications.
In STI testing, speech is modeled by a special test signal with speech-like characteristics. Speech can be described as a fundamental waveform that is modulated by low-frequency signals. Therefore STI employs a complex amplitude modulation scheme to generate its test signal. At the receiving end of the communication system, the depth of modulation of the received signal is compared with that of the test signal in each of a number of frequency bands. Reductions in the modulation depth are associated with loss of intelligibility.