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Abstract
Increasing the amount of descriptive bytes in an audio system should lead to a higher quality signal with less distortion. This project hopes to find a way to reach a higher quality level in its output then any other project done in this lab before. Also, it will be an investigation into FIR filtering, a way of filtering signals with minimal phase shift.
Background
In this project, I will be creating an 8 channel, 12 bit, digital audio mixer. This is in the field of digital audio and digital signal processing. I hope to suppliment the mixer with an array of software FIR filters, to be used to equalize the mixed signal, after all other processing is done on the signal. I hope to find out whether the addition of 4 bits will improve the audio quality that we have seen in previous projects in this class (that have used 8 bit audio,) and to learn more about FIR filters.
Description
An 8 channel audio mixer takes 8 signals, and adds them together to get one signal that is the combination of these signals. It also uses potentiometers/variable resistors to set levels of attenuatation for the signal. In an analog circuit, this is done using op-amps and configuring them as adding amps. Driven by a MC68000 microprocessor, this project should be able to acheive a mix of higher quality, minus any of the problems of analog circuitry, such as distortion, insufficient op-amp speed (slew rate) and phase shift.
The center peice of this project is the MC68000 processor, a 32 bit processor with 16 bit data lines and 22 bit address lines. This will be the main control center of the project, and will be responsable for all of the adding in the project. To take incoming analog signals and digitize them, MAX122 ADC's will be used. MAX122 ADC's are 12 bit analog to digital converters. A single AD7545 will be used to take the digital output and convert it to analog after the signals are mixed together. A lookup table made out of ROMs will be used in this project to speed up multiplication times, since the MC68000 has a slow multiply. A single ADC0809 will be used to take input from the potentiometers, which will be used for signal attenuation in the circuit.
Software for this circuit will be simple, except for the FIR filter. The microprocessor will mainly be used for adding and moving numbers. The FIR filter may wind up being made mainly using hardware.
Problems
The major limitation of this project is time. This circuit requires tons of wiring to be done, and there may wind up being problems with getting all the wiring done. Also, there may be severe problems with error checking, due to the complex wiring.
Another problem lies in creating the software for the circuit. Currently, we do not have any way of compiling 68k assembly. Also, I have no true knowledge of FIR filters, and I may have to teach myself how to design a FIR filter.
