ECE 3551 Microcomputer systems 1

Audio Filtering SystemProfessor: Dr Kepuska

Presented by Kyle Farnum

Audio Manipulation through utilizing three types of filters:

•Low-pass filters

•Band- pass filters

•High- pass filters

The goal of this project was to separate the low, mid and high frequencies from the original audio signal.

Introduction

Implementation• Without any of the buttons being pushed, the original audio

signal will be played.

Pressing PF8 • Once will initiate the first low-pass filter and turn on LED4.

• Twice will initiate the second low-pass filter and turn on LED5.

• Thrice will initiate the third low-pass filter and turn on LED6.

After each time PF8 is pressed, the bass gets more and more distinct. Bass gets deeper and deeper.

ImplementationPressing PF9

• Once will initiate the first band-pass filter and turn on LED4.

• Twice will initiate the second band-pass filter and turn on LED5.

• Thrice will initiate the third band-pass filter and turn on LED6.

After each time PF9 is pressed, the mid range gets more and more distinct. All the high and low frequencies are neutralized. In the project especially when the third band-pass filter is initiated, the vocals of the singer are distinct as the higher and lower frequencies are neutralised.

ImplementationPressing PF10

• Once will initiate the first high-pass filter and turns on LEDs 6& 7.

• Twice will initiate the second high-pass filter and turns on LEDs 5&8.

• Thrice will initiate the third high-pass filter and turns on LEDs 4&9.

After each time PF10 is pressed, the high range gets more and more distinct. All the low and mid frequencies are neutralized. So the audio input gets progressively higher as each high-pass filter is activated.

Designing FiltersAll of the 9 filters were designed in Matlab

using the fdatool. Chebychev type 2 was the design type

utilized for all the filters.The coefficients from the filters were

exported and the integer values were placed in the code as floats in the Process_data section of the code.

Low-pass filters: cutoff frequencies: 4000Hz, 2400 Hz, 1200Hz

High-pass filters: cutoff frequencies: 5400Hz, 7200 Hz, 9600 Hz

Band-pass filters:4000Hz and 5400Hz5600 Hz and 7000Hz7000Hz and 9000Hz

• Below is the transfer function representation of the

IIR filter:

Where B and A are the filter coefficients and z represents the delays.

• We implemented our filters in our code using the direct 2 formula equations:

2

21

1

22

110

1

zAzA

zBzBBzH

mdBmdBmdBmy

mdAmdAmxmd

012

12

12

12

PreparationMade sure that all SW9 pins were on. First 4 controlled

PF 8-11. Last two allow Sport0 to transmit and receive information.

Also make sure that SW12 pins are also activated so that the Sport0 would be connected to the audio codec.

Initialization and enabling the six LED’s and the four Push Buttons

Some of the interrupts were:SPORT0_RX_ISR

FLAG A_ISR

Processprocessor start at main() in main.c. This

program calls a various initialization routines to set up the EZ-Lite boards in a configuration that is needed for audio input/output, then it executes an infinite loop.

This program is an interrupt driven program which means that the computer program only does something when a hardware interrupt is generated. 

The Process_data file contains the user computational functions –( implementation of filters)

In ISR functions will facilitate calling the computational functions and give their output

Results and ConclusionWe were able t separate the low, mid and

high frequencies with the three types of filters used in this project.

The only change that I would make would be to make the cutoff frequencies a bit more distinct.

This was done deliberately though as the idea was to achieve a gradual change in the filtered audio.