|Vocode-esque is an 8 band vocoding
synthesizer with a custom display. This project aims to demonstrate
a technique of signal analysis, decomposition and re-synthesis using
a mixture of analog and digital circuity techniques. Instead of using
DSP (Digital Signal Processor) chips, we used basic electronic components
to build the synthesizer.
|The Sharp bandbass filters and CPU.|
|The board got larger after a while.|
|The type of synthesis here is vocoding:
An input signal is mixed in through an array of eight sharp bandpass
filters. The filters F3db's were spaced linearly across the audible
spectrum. Each filter feeds an integrator. The integrated magnitudes
of each filter band then feed an analog to digital converter. The digital
values are latched into the CPU. We chose to use a 8051 CPU in standalone
configuration. The internal flash of the CPU was programed to perform
two functions: 1. To to update an LED display, witch graphed a representation
of the magnitude of each of the eight frequency bands; 2. To control
eight digital pots on the output stage. The output stage consists of
eight bandpass filters who's F3db's match the input filters. White
noise feeds these filters.
The output of the filters are summed into speaker. The digital controlled pots are controlled by the CPU and attenuate the filters. The desired effect is a reconstructed sound made up from the 8 bands. It is a metallic or robot sound.
|Extra layers are used to fit all the components. The 8051 CPU is programmed in Assembly Language.|
|Laser cut clear acrylics are designed to accommodate the LED array in a circular form. The center of the cylinder is used as a bus for all the wiring.|
|A cylindrical LED array display
is built to show the energy in each of the bands. It is cut out of
clear acrylic, and sandblasted to get a glow effect. The cylinder structure
that holds the LEDs is designed to be visible from different angles.
The center of the cylinder is used as a bus for all the wiring that
goes from LEDs to the LED driver.
This work was the final project for Paul Horowitz and Tom Hayes's Physics 123 Lab at Harvard. Vocode-esque was a great lesson in analog-to-digital and digital-to-analog conversion.
The Art of Electronics