Aaron Gutierrez


John Stobbart


Ismael Chavarria


Cesar Jimenez

Objective

The purpose of this project was to produce a specific purpose audio spectrum analyzer designed to aid the deaf in the vocalization of basic vowel sounds.

Abstract

Soundvision has produced a device called an Audio to Visual Converter (AVC). This AVC is designed to be used to aid the hearing impaired in learning the proper pronunciation of vowel sounds. Soundvision's AVC is a form of spectrum analyzer similar to commercial versions currently available in today's marketplace. What sets the this AVC apart from other analyzers are the specific frequencies filtered from the incoming signal. Only those frequencies needed to distinguish between each vowel sound is used. Another aspect is the AVC’s display. Soundvision's AVC display, which is much larger than those found on readily available commercial analyzers, allows the vocalized sound to be easily viewed. Using the AVC in conjunction with vowel sound template cards (also produced by Soundvision) makes it possible for the user to link his or her spoken sounds to its visual representation, all in real-time. The user, with practice, can then learn how to properly produce basic vowel sounds.

AVC Construction

This audio spectrum analyzer or Analog to Visual Converter (AVC) was designed to be a relatively low-cost and fully self-contained, stand-alone real time audio spectrum analyzer. Four major stages comprise the device: An input stage, a band-pass filter stage, a display stage and a power supply. The entire unit is contained within a single enclosure. Stage one, the microphone input stage, required the design of a small signal amplifier capable of providing an adjustable 20 decibel (db) gain to the input signal level. This gain is necessary to ensure an adequate voltage level is available at the input of stage two as well as providing a level adjustment for the display. Stage two, consists of two banks of band pass filters. Together, these two banks of filters will be individually designed to trap the 20 required frequency bands out of the input signal. Next follows stage three, this stage of the device consists of two modules, a bank of twenty peak envelope detectors and twenty columns of ten light emitting diode (LED) stacks. The peak envelope detector stores the peak voltage value of its input frequency. This voltage level is used to drive the LED stack found at the output of each peak detector. The final stage is comprised of an on-board power supply capable of providing the necessary electrical power to the entire system.

AVC Block Diagram


Issues

Issues resolved concerning the design of stage 1 included a determination of both its input and output impedance. Proper impedance matching ensured a maximum transfer of power from the amplifier. In addition, due to the large number of filter circuits comprising stage two, excessive loading of the output of the input amplifier had to be prevented. This was accomplisehed through the addition of an output buffer stage used to provide a low loss audio distribution to the filters in stage two. Prior to the design of stage two, research aimed at identifying the critical frequencies required by this device was undertaken. This research involved both a study of previous research in this area as well as the use of Spectrogram signal analysis software program. The Spectrogram software allowed the project team to analyze basic sounds with the goal of identifying those frequencies containing the most energy in a given sound. Results of this research indicated that at least 20 frequency bands in the 60Hz to 4kHz frequency range should be selected. . Issues to be resolved concerning the design of this stage included ensuring that each of the active filters had the desired center frequency, gain, quality factor (Q) and Bandwidth (BW). There were many different types of active filters that could be used to obtain the desired effect. Among them the Butterworth filter, which was used in to order to achieve the desired operating parameters, while using relatively few components and having no passband ripple. After all of the previous stages had been designed, an on-board power supply capable of providing the necessary electrical power to the AVC was obtained. Once each individual stage operation had been deemed satisfactory, the entire unit was prototyped, analyzed and debugged. After the design was finalized, a printed circuit board layout was produced using the CAD program ORCAD layout, and a prototype system using these boards was constructed and tested. Next, an equipment enclosure was constructed the completed circuit boards were installed, and a complete operational check of the device performed. Finally, a library of templates consisting of basic vowel sounds was compiled and an operating manual for the device was developed.

AVC Photo Gallery


Pre-amplifier Board-Shown with microphone input jack and gain potentiometer


Filter/Display Driver Board-One of twenty such boards. Each board has the same topology, the filter components being the only difference between the boards.


Filter/Display Driver Boards- Close up of these boards mounted on the enclosure.


Display Board-One "slice" of the display. Twenty of these "slices" were used to form the display.


Display- The entire working Display .


The Audio to Visual Converter (AVC)- A view of the completed system.

Conclusion


After a year of hard work, Soundvision has successfully designed and constructed a relatively low-cost special purpose spectrum analyzer or audio to visual converter (AVC). Soundvision's AVC is a form of spectrum analyzer similar to commercial versions currently available in today's marketplace. What sets the this AVC apart from other analyzers are the specific frequencies filtered from the incoming signal, flexibility of design, and realitive low cost. Together these three factors allow the AVC to be tuned or calibrated in order to display only those frequencies needed to distinguish between each vowel of a particular user. Soundvision's AVC display, which is much larger than those found on readily available commercial analyzers, allows the vocalized sound to be easily viewed. Using the AVC in conjunction with vowel sound template cards (also produced by Soundvision) makes it possible for the user to link his or her spoken sounds to its visual representation, all in real-time. We believe that the user, with practice, can then use this device as an aid to learning how to pronounce basic vowel sounds.