ECE 3551 – Microcomputer Systems 1
Fall 2010
Siobhan Ireland
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Overview of Project
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Generating Musical Notes
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Filtering Audio Input
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Improvements
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Conclusion
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The initial idea for my project was to use the
BF533 EZ-Kit Lite board to create an
electronic vocal coach
This project could have real world application
in helping people train their vocal ability
I implemented the project by splitting it into
two parts: generating musical notes, and
filtering audio input

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I calculated note frequencies over a range of
four octaves and from each octave chose one
note – corresponding with the four push
buttons
The frequencies were found using the
equation:
Frequency  440  2
n
12
Hz
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The algorithm for generating the notes is:
  f0  
xn  A sin 2  n  A sin 2F0 n  A sin 0 n
  f s  
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Which in code translated to:
y = 7*x*sinf[w0*n]
if(note==1)
//note C3
{
n %= 367;//nmax
y=7*x*sinf(0.01712335 *n);
y0=(int)(y);
//send output to left and right audio channels
iChannel0LeftOut=y0;
iChannel0RightOut=y0;
}
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I had a few difficulties getting the code working

Once working I tested various values for amplitude

The code for generating musical notes was
successful

Push
Push
Push
Push
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Demonstration
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button
button
button
button
PF8 = note C3
PF9 = note D4
PF10 = note F5
PF11 = note A6
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The initial purpose for this section of the
code was to accept user input in the form of
singing and analyze which octave the
frequency lies in
I chose first to test the code using input in
the form of a song from my I-pod
The filter values were chosen based on the
calculated octave frequency values

The algorithm for IIR filters is:
b0  b1 z 1  b2 z 2
H z  
1  a1 z 1  a 2 z 2
d m  xm   a 2 d m  2  a1 d m  1
ym  b2 d m  2  b1 d m  1  b0 d m


The filters were created using MATLAB
fdatool
IIR filters were chosen over FIR filters because
they have less coefficients and produce
clearer, crisper filtering

The c code for the IIR filters is given below:
void low_lowpass_filter(void)
{
int i = 0;
//reset loop (row) counter
//set input equal to iChannel0LeftIn shifted by 8
//iChannel0LeftIn>>8 shifts the original audio from 24 bits to 16 bits
x_input = iChannel0LeftIn<<8;
for(i=0; i<13; i++)
//for row 0 to row 13
{
//implementation of algorithm
//calculate input from d[m] = x[m]-a2d[m-2]-a1d[m-1]
D_low[i][0] = x_input - (low_lowpassA[i][2]*D_low[i][2]) - (low_lowpassA[i][1]*D_low[i][1]);
//calculate output from y[m] = b2d[m-2]+b1d[m-1]+b0d[m]
y = (low_lowpassB[i][0]*D_low[i][0]) + (low_lowpassB[i][1]*D_low[i][1]) +
(low_lowpassB[i][2]*D_low[i][2]);
x_input = y;
//set x_input to previous value of y
D_low[i][2] = D_low[i][1];
//shift values stored in array
D_low[i][1] = D_low[i][0];
//shift values stored in array
}
//shift value of y (typecast as int) by 8 bits from 32 bits to 24 bits
//send output to left and right output channels
iChannel0LeftOut=(((int)y)>>8);
iChannel0RightOut=(((int)y)>>8);
}
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Initially I applied band-pass IIR filters with
frequencies corresponding to the octaves. There
was no audible change to the input
Next I applied band-pass IIR filters with large
frequency ranges. There was still no audible change
I then switched to low and high-pass IIR filters with
original frequency values. Still no change was heard
Lastly I applied low and high-pass IIR filters with
large frequency ranges. They successfully altered
the audio input

There was no point at this stage of
development to add a microphone, as the
filters wouldn’t work as originally planned

No button, - LED 9 - original audio
PF8 pressed - LED 4 - low range filter
PF9 pressed - LED 5 -low-mid range filter
PF10 pressed - LED 6 - high-mid range filter
PF11 pressed - LED 7 - high range filter
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Demonstration
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Lab access
Equipment access
Improve filters
Add microphone
Design user feedback
Combine codes
Eventually extend number of notes played
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Overall I consider the project successful

The project utilized and built upon
knowledge gained through lecture and lab


Generating musical notes was new to me and
was implemented successfully
Filtering audio was adapted from lab work
and while it works correctly, it needs further
development to work as originally planned