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.