Description
Dr. Chao Wang
EEE203 Signals and Systems I
Page 1 of 3
Lab: Opera in Italy, Anyone?
Your friend Bob is an avid opera fan. He has a short recording of an opera singer in a sound proof
anechoic (echo free) room. He?s very interested in hearing how his recording would sound like in an
opera house and a church, such as the Milan Opera House in Italy and the St Nicolas Church in Prague as
shown in Figure 1. As a student enrolled at ASU, he also think it would be fun to hear how the singing
would sound like if it was played at Grand Canyon.
Figure 1. Milan Opera House in Italy, St Nicolas Church in Prague, and Grand Canyon in Arizona
To help make Bob?s wishes come true, let?s start with some background knowledge on convolution
reverb1. It is a technique used in audio signal processing to simulate an audio environment.
Reverberation2 is the persistence of sound after it is produced and it is the result of sound wave
reflections in an enclosed environment. Figure 2 and Figure 33 shows the traveling paths of sound wave
in an auditorium. When a sound impulse is played, many different copies of the sound, either direct or
reflected, reached the listener some time later due to the sound wave travel delay. The collection of
many reflected sounds are called reverberation.
1
https://en.wikipedia.org/wiki/Convolution_reverb
https://en.wikipedia.org/wiki/Reverberation
3
http://hyperphysics.phy-astr.gsu.edu/hbase/Acoustic/reverb.html#c2
2
Dr. Chao Wang
EEE203 Signals and Systems I
Page 2 of 3
Figure 2. Direct and reflected travel paths of a sound wave
Figure 3. Sound impulse and the received pulses from direct and reflected paths
The reverberation effect is an importance characteristic of a space and can be captured and be used to
simulate the environment. As shown in Figure 3, it is generated by recording an ideal impulse response
of the space. In mathematics, an impulse is infinitesimally narrow in time. In reality, it is approximated
by a short loud sound such as a clap, a gas starter pistol (the type used to start athletics races) or a
balloon burst. When this impulse sound is played in the space, a recorder is set at a location of interest
and is used captured the received wave and its reflections. As you are probably aware, if you record the
impulse at different sections of a concert hall (front, back, balcony), the impulse responses would be
different due to different travel paths of the sound wave. Once you have the impulse response of a
space, you can use it to simulate the space and hear its sound effect without physically being there. You
can simply convolute your audio file with the impulse response of the space. You might wonder what a
piano melody might sound like inside a cavern. How about drum beats in the middle of an old church?
Lab Objectives:
1. Understand the concepts of system input, output and impulse response.
2. Import data from a file.
Dr. Chao Wang
EEE203 Signals and Systems I
Page 3 of 3
3. Plot a digital signal in the time domain.
4. Use the convolution function ?conv? to generate system output given input and impulse response.
Lab Tasks:
Submit MATLAB script and plots in a signal PDF file.
1. Download the sound file ?singing.wav? and the impulse responses ?ScalaMilanOperaHall.wav?,
?StNicolasChurch.wav? and ?GrandCanyon.wav?.
2. Download the MATLAB script ?lab_conv_reverb.m?. Complete the script and submit the completed
script.
a. In the script, an example is shown to import, plot and play an audio (song) file.
b. Your job is to 1) import, plot and play the impulse response, 2) convolute the impulse
response with the song, and 3) plot and play the convoluted output.
3. Submit the MATLAB plots for each scenario/location (three in total). On each plot there should be
three subplots, the song as the first subplot, the impulse response as the second plot and the
convoluted song as the third plot.
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