Echo and Reverberation
1 Introduction
Echo and Reverberation are two of the simplest applications of Digital Signal
Processing (DSP). This laboratory shows how models of Echo and Reverberation
can be designed using MATLAB and Simulink, and run them in real-time on the
Texas Instruments C6000 DSPs.
1.1 Objectives
Design models of Echo and Reverberation for the Texas Instruments
C6000 family of DSP devices using MATLAB and Simulink.
Modify an existing Simulink model.
Run the model in real-time on the Texas Instruments C6713 DSK.
1.2 Level
Beginner - Assumes only very basic knowledge of MATLAB and Simulink. It is
suitable for students with limited knowledge of Texas Instruments DSPs.
1.3 Hardware and Software Requirements
This laboratory was originally developed using the following hardware and
software:
MATLAB R2006b with Embedded Target for TI C6000.
Code Composer Studio (CCS) v3.1
Texas Instruments C6713 DSK hardware
Microphone and computer loudspeakers/headphones
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2 Simulation
We shall start by running the Echo and Reverberation Simulink models. These
use .wav files as the inputs.
2.1 Echo using Wave File
2.1.1 Opening the Echo Simulink Model
From MATLAB, open EchoUsingWav.mdl
Figure 1 Echo using .wav File
Run the model and listen to the effect of the delay.
2.1.2 Changing the Delay Time
Double-click on the Delay block and change the Delay (samples) to a different
value.
Figure 2 Changing the Delay Time
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Run the model and hear how the effect has changed. Try a few different settings
between 100 and 20000 Delay (samples).
2.2 Reverberation using Wave File
2.2.1 Opening the Reverberation Simulink Model
From MATLAB, open ReverberationUsingWav.mdl
Figure 3 Reverberaton Using .wav File
2.2.2 Changing the Delay Time
Double-click on the Delay block. Change the Delay (samples) to a different
value then run the model and listen to the effect.
2.2.3 Changing the Gain
Double-click on the Gain block. Change the Gain to 0.95 then run the model.
Listen to the effect.
Figure 4 Changing the Reverberation Gain
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2.2.4 Questions
Why does Reverberation require a shorter delay time than echo?
What
effect
does the Gain block have
on
the stability of the
reverberation system?
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3 Real-Time Model for TI C6713 DSK
3.1 Texas Instruments C6713 DSK Setup
Figure 5 Texas Instruments C6713 DSK Setup
Alternatively, you can use computer loudspeakers.
Connect the C6713 hardware to a USB port of the computer and turn on the
supply to the board.
If the board is powered, then the green LED lights on the board will come on
during self-test.
3.2 Starting Code Composer Studio
The stages required to implement Echo and Reverberation are now described.
3.2.1 Starting Code Composer Studio
Start Code Composer Studio for C6713 DSK and use Debug -> Connect
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Figure 6 Startup Screen for Code Composer Studio (CCS)
3.2.2 Opening an Existing Model
Start MATLAB 7.3.0 R2006b
In the top left hand corner of the MATLAB screen, select File -> Open.
Figure 7 Opening an Existing Model
The following screen will appear.
Figure 8 Selecting an Existing Model
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Highlight C6713_Audio_Template then click on Open.
3.2.3 Viewing the C6713 Audio Template
The C6713_Audio_Template is now displayed.
Figure 9 The C6713 DSK Audio Template
3.2.4 Overview of the Complete Echo Subsystem
You are now going to implement the Echo Subsystem shown below.
Figure 10 The Complete Echo Subsytem
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3.2.5 Implementing the Echo Subsystem
Double click on the Effect 1 subsystem block. An empty model will appear.
Figure 11 The Blank Effect 1 Subsystem
You will now drag-and-drop some library components onto the model.
3.2.6 The Simulink Library Browser Commonly Used Blocks
Select View -> Library Browser. Expand the Simulink section.
A list of available blocks will appear. We are initially interested in the Commonly
Used Blocks.
Figure 12 Commonly Used Blocks
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From Commonly Used Blocks, drag-and-drop a Gain block, a Sum block and
two Data Type Conversion blocks onto the model.
3.2.7 The Simulink Library Browser - Discrete
From the Simulink Library Browser, select Discrete. Highlight Integer Delay
and drag-and-drop this block onto the model.
Figure 13 Discrete Blocks
3.2.8 Setting the Integer Delay Time
The delay time will be 0.5 seconds. Using a sampling rate of 8000 Hz, this
requires 8000 x 0.5 = 4000 samples. In the equation given in the lecture, this
would make N = 4000.
Double click on the Integer Delay block. Change the Number of delays field to
4000, then click on OK.
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Figure 14 Setting the Integer Delay Time
3.2.9 Setting the Output Data Conversion to Single
We want to set the gain to 0.9. If you multiply an integer value by 0.9, then the
value 0.9 will be rounded-down to zero. Instead, you need to convert the integer
value to a floating-point value such as single, and then convert it back later.
Click on OK.
Figure 15 Setting the Data Conversion to Single
3.2.10
Setting the Delay Gain
We required that 0.9 of the delayed input is added to the normal input. Therefore,
set the Gain to 0.9 then click on OK.
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Figure 16 Setting the Echo Delay Gain
3.2.11
Setting the Output Data Conversion to int16
Double click on the second Data Type Conversion block. Set the Output data
type mode to int16. This is compatible with the DAC on the C6713 DSK.
Figure 17 Data Type Conversion to 16-bit Integer
3.2.12
The Completed Echo Subsystem
Join the blocks as shown and add a title.
Figure 18 Joining the Blocks
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3.2.13
Returning to the Parent System
From the Toolbar, select the Up Arrow icon. This returns you to the next higher
level.
Figure 19 Returning to the Parent System
3.3 The Reverberation Subsystem
The next subsystem to be implemented will be Reverberation.
3.3.1 Overview of the Completed Reverberation Subsystem
We are now going to implement the Reverberation System shown below.
Figure 20 Overview of the Reverberation Subsystem
Note that the reverberation subsystem is very similar to that of echo. We will cutand-paste from the Echo Subsystem
3.3.2
Opening the Effects 2 Subsystem
From the C6713 Audio Template top level, double-click on the Effect 2
subsystem.
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Figure 21 The Blank Effect 2 Subsystem
3.3.3
Copying a Block from the Echo Subsystem
Double click on the Effect 1 subsystem. Cut-and-paste a copy of the echo block
as follows: while left-clicking the mouse, mark the area to be copied.
Figure 22 Outlining the Block to be Copied
Release the left button on the mouse.
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Figure 23 Block to be Copied is Marked
From pull-down menu, select Edit -> Copy (or Ctrl + C)
3.3.4
Blocks Dropped onto Effect 2 Subsystem
Return to the Effect 2 subsystem and Edit -> Paste (Ctrl + V) into the model.
Figure 24 Blocks Dropped onto Subsystem
3.3.5
Flipping the Blocks
The blocks are facing the wrong way. Turn them round using Format -> Flip Block.
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Figure 25 Flipping the Blocks
3.3.6 Changing the Integer Delay for Reverberation.
Because the sound goes round several times with reverberation, a shorter delay
time can be used. Here the delay time is 0.1 seconds.
Figure 26 Delay Time for Reverberation
Set the Number of delays to 800 then click on OK.
3.3.7 Completing the Reverberation Subsystem
Connect the blocks as shown below. Change the title to Reverberation
Subsystem.
Figure 27 The Completed Reverberation Subsystem
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3.3.8 Returning to the Parent System
From the Toolbar, select the Up Arrow icon. This returns you to the next higher
level.
Figure 28 Returning to the Parent System
3.4 The Improved Echo Subsystem
The final subsystem to be implemented will be Improved Echo. This is based on
the Echo subsystem, but with several delay paths.
3.4.1 The Complete Improved Echo Subsystem
Double click on the Effect 3 subsystem box. The required components are
shown below.
Figure 29 The Improved Echo Subsystem
3.4.2 Implementing the Improved Echo Subsystem
You should now have enough knowledge to implement this subsystem block
without further assistance. This time you are on your own!
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3.4.3 Building the Model
Select Tools -> Real-Time Workshop -> Build Model.
Figure 30 Building the Model
3.5 Running the Model
3.5.1 Microphone Straight Through to Loudspeakers
To check out the microphone and loudspeakers, set the DIP switches on the
C6713 DSK as follows:
Figure 31 Switch Position 0
The microphone is fed directly to the loudspeakers without any digital signal
processing.
3.5.2 Switch Position for Echo
To run the Echo subsystem, set the DIP switch to 1.
Figure 32 Switch Position 1 for Echo
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3.5.3 Switch Position for Reverberation
To run the Reverberation subsystem, set the DIP switch to 2.
Figure 33 Switch Position 2 for Reverberation
3.5.4 Switch Position for Improved Echo
To run the Improved Echo subsystem, set the DIP switch to 3.
Figure 34 Switch Position 3 for Improved Echo
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4 Some Things to Try
4.1 Change the Echo Delay
Change the value of the Integer Delay block for echo. Listen to the effect of
using short and long delays. Set the delay time to a large value and sing a round
such as Frere Jacques or Row, Row, Row your Boat.
4.2 Change the Amount of Reverberation Gain
In the Reverberation Subsystem block, change the Gain from 0.8 to higher
and lower values. Notice how the system can become unstable if the gain is too
large.
4.3 Modify the Improved Echo Subsystem
In the Improved Echo Subsystem, you may wish to experiment with the number
of delay elements, the delay times and the amounts of gain. Try to make the
echo as realistic as possible.
4.4 Create Your Own Subsystem
Add your own subsystem block and add your own signal processing. You might
want to design a subsystem with both echo and reverberation.
MATLAB and Simulink are registered trademarks of The MathWorks, Inc. See
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