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This module is a laboratory assignment to implement an echo function.

Introduction

In this laboratory you will use a program that gathers data from an A/D converter, processes the data, and outputs to a D/A converter. The signal processing portion will be added by you to perform an echo function. After this laboratory you should:

  • Understand how data is received from an A/D converter and sent to a D/A converter
  • Understand how signal processing is done in "real-time"
  • Be able to implement a simple signal processing algorithm using "block processing" techniques

Laboratory assignment

In the laboratory you will be making a delay function or an echo. To make an echo you will need to delay the data that is coming into the DSP. This is usually accomplished using a buffer that is used to store previous input values. Use a circular buffer to store the input data. The length of the buffer is determined by

N = Delay SampleRate size 12{N= ital "Delay" cdot ital "SampleRate"} {}

In order to implement the delay an array of sufficient size must be defined. When a function is called, the local variables will go onto the stack. The stack is usually small compared to other memory sections. Therefore, the number of local variables for a function is limited. Since the array for storing the previous inputs will be large, the array should be stored somewhere else in memory besides on the stack. If the Memory Model in the build options is set to Far Aggregate then the global variables and the local static variables will be put into the .far section. This section can be set to the large external memory. Therefore, the array that stores the delay values should be defined as either a global or static local variable . A static local variable is a variable that is not initialized each time a function is called. The static variable will retain the value it had the last time the function was called. To make a static variable just use the static keyword in front of the variable definition.

static int static_var, static_array[10];

You need to make sure the .far section is set to a large memory section. For our project, set it to the SDRAM memory. To change the location of the .far section in the project you should:

  • Open the project DSK6713_audio.pjt
  • Open the configuration file DSK6713_audio.tcf
  • Right click on System->MEM and open Properties
  • Click on the Compiler Sections tab
  • On the pull down menu next to the .far section select SDRAM

Pre-laboratory

  • If your sample rate is 8000 Hz and you want a delay of 1/2 second, how long should your delay buffer be?
  • The main loop in the default I/O program simply inputs a block of data and then outputs a block of data. You need to modify the main loop so that it will take an input sample, store it in the circular buffer and output the sample that is delayed by 1/2 second. Your code should implement a circular buffer . Also, make sure you initialize the buffer with zeros so that you won't output whatever happens to be in the memory.
  • What is the transfer function, H(z), of the system in the following figure? What is the difference equation? What would happen if you set the feedback gain to a value greater than 1?
  • Write another program that will implement a fading echo shown in following figure. The output of the delay is fed back to the input of the delay and added to the input.

Laboratory

Part 1

  • In this part you will just get the template project working that simply outputs whatever was input.
  • Open the project DSK6713_audio.pjt .
  • Change the parameters in the DSK6713_audio.c file so that the sampling rate is 8000 Hz and the input is from the microphone.
  • Connect a microphone to the DSK board microphone input and the speakers to the line out.
  • Build, load and run the project.
  • Verify that as you speak into the microphone you hear yourself on the speakers.

Part 2

  • Modify the program DSK6713_audio.c so that one channel of output is delayed by 1/2 second. Make sure to define your stored samples array as a global or static array in external memory.
  • Build, load and run the project.
  • Demonstrate that you get a 1/2 second delay in the output.

Part 3

  • Modify the program DSK6713_audio.c to implement the fading echo.
  • Build, load and run the project.
  • Demonstrate that you get a 1/2 second delay in the output.
  • What would happen if you set the feedback gain to a value greater that 1?

Questions & Answers

the difference between the two cells
Obeng Reply
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Isaac Reply
why drinking excess alcohol causes thirst and dehydration
uwikuzo Reply
what is reproduction
smart Reply
it is d act of bringing young ones to life
Oyebanji
to ensure survival of a species🚴‍♀️
Michelle
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Collins
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smart
a cell is the smallest unit of a living thing. so we all have cell
smart
It is the formation of a zygote resulting from the fusion of the sperm cell with the ovum.Thus,this results in the production of new species which are genetically dissimilar from their parent cells.
Pallavi
what is size of cell
Mohd Reply
what is size of Hart
Mohd
nanometers=um sign thingie
Michelle
microns=nanometers
Michelle
monomers and polymers of nucleic acids?
Jyrl Reply
dna and rna involvement
Michelle
give me the elements of the soil
Iguma Reply
Air, water, organic matter, inorganic matter
Tshwano
soil water humus air
Veronicah
yap
Beloved
silica, iron
Patience
potassium, sulfur, calcium, carbon
Michelle
what is cell
iyaji Reply
A cell is a smallest fundamental unit of a living organisms.
Kem
the basic structural and functional unit of life
Patience
what is size of cell
Mohd
all things are made up of.....all things cannot exist without pre-exisiting cells...check out the 16th ce tury to learn more about microscope use and cells. i will give a hint: Mr. L.
Michelle
we are all made of cells
Michelle
Nutrition - sensitive intervention
Therowda Reply
what does the sori In fern mean
arhin Reply
biology is the study .exactly what is life?
Jerry
i'm sorry , the study of life
Jerry
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Frankyx Reply
through genetic fingerprinting where specific DNA sequences in a person genome can be identified.
Pallavi
by help of genetics and DNA test
Meerbadini
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Frankyx
environmental biology
Ojesola Reply
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Ojesola
What is anabolism
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the break down of substance
Aunty
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36
Treasure
32
Favour
32
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32 teeth
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32
OLAMIDE
32 (or 36 including the wisdom teeth)
Hailey
32
Sani
26?🤓
Michelle
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Ayo Reply
hypothalamus negative feedback vs. postive feedback systems.
Michelle
it is the maintenance of a steady internal environment.it is controlled largely by the brain especially the hypothalamus.
Oyebanji
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Source:  OpenStax, Dsp lab with ti c6x dsp and c6713 dsk. OpenStax CNX. Feb 18, 2013 Download for free at http://cnx.org/content/col11264/1.6
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