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(Solved) Barukh Rohde University of Florida Fall 2016 Lab 3: Music Synthesis with Sinusoidal Signals Introduction Sinusoids are used in a wide variety of...


I need help with 1.6 on the first part of the lab attached, I am lost.

Barukh Rohde University of Florida Fall 2016 Lab 3: Music Synthesis with Sinusoidal Signals
Introduction
Sinusoids are used in a wide variety of applications. Perhaps the most obvious one is in music. A
musical note is a simple sinusoid of the form (2 + ), with amplitude , frequency ,
and phase . A melody, or musical voice, is composed of an ordered list of notes and rests. A
musical composition is, simply put, a sum of melodies. Every pulse in a musical composition is
therefore a sum of sinusoids of the form:
() = ∑ ( + ) In this lab, you will synthesize some musical pieces, including Mary Had a Little Lamb, Fugue
#2 for the Well-Tempered Clavier by Bach, Hava Nashira by Barukh, and Treat You Better by
Shawn Mendes. Because this is a rather complicated programming assignment, you should
start as soon as possible and take advantage of all class sessions and TA office hours.
Debugging tools can be very helpful when troubleshooting larger programs like the one you
will write in this lab. To learn about MATLAB debugging tools (you don’t need to submit your
help results), type help debug in the command window. Lab Part One
1.1 A Function to Play a Note
Piano keyboards are laid out as illustrated by the following image: •
•
•
• C4 refers to the C-key in the fourth octave. C4 is also called middle-C.
A4 is also called A-440, because its frequency is 440 Hz.
Every key is given a key number. The key number of middle-C is 40.
The frequency of any key can be found by substituting its key number into the formula: −49
12 = 440(2 EEL3135: Intro to Signals & Systems ) 1 Lab 3: Music Synthesis withSinusoidal Signals Barukh Rohde University of Florida Fall 2016 Remember that when we construct a sinusoid through MATLAB, we are in fact constructing a
sampled sinusoid
[] = ( ) The Sampling Theorem tells us that to recover a continuous signal from its samples without
aliasing, fs must be at least two times greater than the largest frequency component.
soundsc(xx, fs)will output sound recovered from the sample vector xx at a rate of fs
samples per second. Use this to judge how your synthesis is doing as you work on the lab. In
music synthesis, common choices for sampling frequency f s are 8000 Hz, 11025 Hz, or multiples
of 11025.
Write a MATLAB function to produce a desired note for a given duration at a given complex
amplitude. Use the following skeleton code to write your function:
function xx = key2note(X, keynum, dur)
% KEY2NOTE Produce a sinusoidal waveform corresponding to a given
piano key number
% usage: xx = key2note (X, keynum, dur)
% xx = the output sinusoidal waveform
% X = complex amplitude for the sinusoid, X = A*exp(j*phi).
% keynum = the piano keyboard number of the desired note
% dur = the duration (in seconds) of the output note
fs = 8000;
tt = (1/fs):(1/fs):dur;
freq = %<=============== fill in this line
xx = real(
); %<=============== fill in this line
end For the freq= line, use the formula given above to determine the frequency for a sinusoid in
terms of its key number. You should start from a reference note (middle-C or A-440 is
recommended) and solve for the frequency based on this reference. Fill in the xx = real()
line to generate the actual sinusoid as the real part of a complex exponential at the proper
frequency. EEL3135: Intro to Signals & Systems 2 Lab 3: Music Synthesis withSinusoidal Signals Barukh Rohde University of Florida Fall 2016 1.2 Synthesize a Song – Mary Had a Little Lamb that NEVER grew up!
Multiple notes can be played in order by concatenating their row vectors as follows:
xx = [x1 x2]; Use glottalkey2note()to write a script, play_glottallamb.m, that plays a series of
notes. Use the following skeleton code to write your script:
% --------------play_lamb.m-------------- %
mary.keys = [44 42 40 42 44 44 44 42 42 42 44 47 47];
% NOTES: C D E F G
% Key #40 is middle-C
mary.durations = 0.25 * ones(1,length(mary.keys));
fs = 8000; % 11025 Hz also works
xx = zeros(1, sum(mary.durations)*fs + length(mary.keys));
n1 = 1;
for kk = 1:length(mary.keys)
keynum = mary.keys(kk);
tone = % <------- Fill in this line
n2 = n1 + length(tone) - 1;
xx(n1:n2) = xx(n1:n2) + tone; %<------- Insert the note
n1 = n2 + 1;
end
soundsc(xx, fs) a.
b. Generate the sound and play it for a TA. Have your TA check you off for this section.
(If you can’t finish this in time for the TA to check it off, submit it as a .wav file.)
Plot the frequency-time spectrogram of Mary using the function specgram(xx,
512, fs). Notice that you can zoom in to show the order of notes. Try varying the
window length (the second function argument) to get different looking spectrograms
if needed. (Note; specgram doesn't work for some students; if this is the case, use
"plotspec" instead). 1.3 Structures
Now that you’ve received an introduction to musical notes, and you’ve played a scale, you’re
going to play something a little more complicated. MATLAB allows for structures, which
group information together. A structure, which is a data type, is used to represent information
about something more complicated than what can be held by a single number, character, or
boolean or an array of any one of them. For example, a Student can be defined by his or her
name (an array of characters), GPA (a double), age (an integer), UFID (a long integer), and
more. Each of these pieces of information can be labeled with an easily understood descriptive
title, and then combined to form a whole (the structure).
Structures give us a way to "combine" multiple types of information under a single variable.
The nice thing about structures is that they allow us to use human-readable descriptions for
our data.For example, every note in a melody can be characterized as a list of notes, each one of EEL3135: Intro to Signals & Systems 3 Lab 3: Music Synthesis withSinusoidal Signals Barukh Rohde University of Florida Fall 2016 which starts at a specified pulse, and is played for a specified duration. We can define three
separate arrays for one melody:
melody_noteNumbers
melody_durations
melody_startPulses = [40 42 44 45 47 49 51 52];
= [1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5];
= [1 3 5 7 9 11 13 15]; But it is generally better to define a melody as a structure containing three fields, denoted as
structurename.fieldname:
melody.noteNumbers
= [40 42 44 45 47 49 51 52];
melody.durations
= [1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5];
melody.startPulses
= [1 3 5 7 9 11 13 15]; The structure is now a type, of which there can now be vectors:
melody(1).noteNumbers
melody(1).durations
melody(1).startPulses
melody(2).noteNumbers
melody(2).durations
melody(2).startPulses =
=
=
=
=
= [40 42 44 45 47 49 51 52];
[1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5];
[1 3 5 7 9 11 13 15];
[40 42 44 45 47 49 51 52];
[1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5];
[1 3 5 7 9 11 13 15]; This is almost ALWAYS a better way to go then to use a group of arrays or even a cell
array.To learn more about structures, examine and run the following code:
x.Amp = 7;
x.phase = -pi/2;
x.freq = 100;
x.fs = 11025
x.timeInterval = 0:(1/x.fs):0.05;
x.values = x.Amp*cos(2*pi*(x.freq)*(x.timeInterval) + x.phase);
x.name = 'My Signal';
x
%---- echo the contents of the structure "x"
plot(x.timeInterval, x.values)
title(x.name) 1.4 The Evenly-Timed First Voice EEL3135: Intro to Signals & Systems 4 Lab 3: Music Synthesis withSinusoidal Signals Barukh Rohde University of Florida Fall 2016 Now that you’ve received an introduction to musical notes, and you’ve played a scale, you’re
going to play something a little more complicated.
You have been given a data file called barukh_fugue.mat, which contains an array of
structures called theVoices, a structure array of the same form as melody above. theVoices
is composed of three voices, each voice of which is characterized by three vectors: durations,
noteNumbers, and startPulses.The first voice’s notes are accessed as the vector
theVoices(1).noteNumbers Modify your play_mary.mcode to create a new function, play_firstvoice_even.m, to
play each note in the first voice of the BarukhFugue for 0.5 seconds each. Have your TA check
this off. If you can’t finish this in time, submit as a .wav file on Canvas.
1.5 The Correctly-Timed First Voice
Something sounded a little bit off with that, didn’t it? That’s because in the melody, the notes
aren’t meant to all be played for the exact same amount of time. Each note is meant to be
played for a specified duration, or number of pulses. Provided that there are no intended breaks
between notes, a melody can be constructed from a vector of noteNumbers and a vector of
durations. These two vectors will have the same length; every
theVoices(1).noteNumbers(i) will have a matching
theVoices(1).durations(i). Modify your play_firstvoice_even.mcode to create a new function,
play_firstvoice.m, to play each note in the first voice for its correct duration of pulses,
with each pulse being 0.25 seconds long. Again, have your TA check this off. If you can’t finish
this in time, submit as a .wav file on Canvas.
1.6 Silence and startPulses: Construction of the Better Fugue
Balance is an important part of music. Sometimes, multiple musical voices are simultaneously
playing. But sometimes, a given voice is silent in favor of another voice. Sometimes, both voices
are silent. We can denote silent periods as time after one note has ended, but before the next
note has begun. Suppose a note of noteNumber 49 starts at pulse 13, and has duration 2; and
the next note of noteNumber 52 starts at pulse 16 and has duration 1. Then the musical voice
is to play Middle A for two pulses, it is to be silent for one pulse, and then it is to play High C
for one pulse. Thus, by incorporating information about theVoices(i).startPulses, in
addition to theVoices(i).durations and theVoices(i).noteNumbers, we can incorporate
silent periods into our musical reconstruction.
Using the startPulses, durations, and noteNumbers properties of each voice in
theVoices, construct the three melodies in the Barukh Fugue and add them together. EEL3135: Intro to Signals & Systems 5 Lab 3: Music Synthesis withSinusoidal Signals Barukh Rohde University of Florida Fall 2016 The MATLAB data file better_fugue.mat is of a similar structure as barukh_fugue.mat,
also containing a theVoices array of structures, but this time with five voices. Using your
barukh_fugue code: Add the five voices, from theVoices in better_fugue.mat, together
to produce the Better Fugue. Note that there may have been errors in the way that you
produced the barukh_fuguethat aren’t noticeable in the better_fugue; the better_fugue
is a bit harder. Produce the Better Fugue, save it as a .wav file, and submit it on Canvas
alongside your lab document. There is no password here - submit the .wav file. This ends Part
1 of this lab.
1.8 Some Help with the Above
The function you create will be similar to your play_scalefile, with the exception that there
will be multiple overlapping melodies and the notes will not all be the same duration. Because
this is a rather complicated programming assignment, you should start as soon as possible and
take advantage of all class sessions and TA office hours.
Remember to reference arrays in the structure. For example, if you wanted to reference the
note numbers in the code to find the length, you would have to say
length(theVoices(i).noteNumbers) The skeleton code for your function is provided below:
function song = playSong(theVoices)
% PLAYSONG Produce a sinusoidal waveform containing the
combinationofthe different notes in theVoices
% usage: song = playSong ()
% song = the output sinusoidal waveform
loadbarukh_fugue.mat
fs = 8000;
spp = % seconds per pulse, theVoices is measured in pulses with 4
pulsesper beat
% Create a vector of zeros with length equal to the total number
ofsamples in the entire song
song = % vector of zeros
% Then add in the notes
fori = 1:length(theVoices) % Cycle through each set of notes
% Convert data arrays to appropriate units
for j = 1:length(theVoices(i).noteNumbers) % Cycle througheach note
in aset
note = % create sinusoid of correct length to represent a
single note
locstart = % index of where note starts
locend = % index of where note ends
song(locstart:locend) = song(locstart:locend) + note;
end
end
% Use audiowrite() to generate WAV file
end EEL3135: Intro to Signals & Systems 6 Lab 3: Music Synthesis withSinusoidal Signals Barukh Rohde University of Florida Fall 2016 Timing (nothing to submit for this subsection)
The time duration of a single pulse will determine the speed of the song. This is typically
specified in beats per minute. You can perform a series of conversions to convert beats per
minute into seconds per pulse, given that there are 4 pulses per beat and beats_per_minute
= 120.
beats_per_minute = 120;
beats_per_second = beats_per_minute / 60;
seconds_per_beat = 1 / beats_per_second;
seconds_per_pulse = seconds_per_beat / 4; Don’t forget to submit your PDF file, too! EEL3135: Intro to Signals & Systems 7 Lab 3: Music Synthesis withSinusoidal Signals Barukh Rohde University of Florida Fall 2016 Lab Part Two
2.1 Construction of the Bach Fugue
The MATLAB data file bach_fugue.mat is of the same structure as barukh_fugue.mat,
also containing a theVoices array of structures. Add the three voices from theVoices in
bach_fugue.mat, together to produce the Bach Fugue. Have your TA check this off.
(Alternately, if you can’t finish this in time, submit as a .wav file on Canvas.) 2.2 Musical Tweaks - Enveloping
After creating the barukh_fugue, you may notice that the product sounds artificial. This is
because it is created from pure sinusoids. In this section, you will incorporate an envelope into
your music synthesis process in order to improve the quality of the final product.
When played by an instrument, notes are not single pure evenly-amplified tones. Their
amplitudes change over the course of a single note, with attack, decay, sustain, and release parts of
a note, together making up an ‘ADSR’ profile. Enveloping creates short pauses between musical
notes, as a scaling vector where all values are between 0 and 1. Envelopes can be implemented
in the synthesis process by multiplying each note by an enveloping function E(t). E(t) should be a mathematical representation of the above. You can get such a curve by using
the linspace()or hanning(). The hanning() function is useful here, as it gets the job
done since it's a bell-shaped curve on a scale from 0 - 1. These correlate to relative magnitudes
and durations of each stage. The envelope E is multiplied (dot multiplied) by each note in the
signal, scaling their amplitudes accordingly. As E(1)and E(length(note)) should both be
zero, the values of the vector should fade in-and-out, reducing the roughness produced in
synthetic note-to-note transitions. Your job here is to improve the sound quality.
Hint 1:The function interp1()may be useful in this section.
Hint 2:You’ll want to make sure that your note and E are the same length.
Hint 3:Previous generations of students have found the Hanning Window to be an effective
envelope.
Implement an envelope to improve the sound of your Bach Fugue. Save it as bach_envelope.wav
and submit it on Canvas. EEL3135: Intro to Signals & Systems 8 Lab 3: Music Synthesis withSinusoidal Signals Barukh Rohde University of Florida Fall 2016 Note: grading here is based on your ability to improve the sound quality. This part is
intentionally left vague; we want you to be creative here!
2.3 Musical Tweaks – Fourier Series of aTrumpet
Remember that any real-world periodic signal can be written as a sum of sinusoids whose
frequencies (in Hertz) are integer multiples of the fundamental frequency. The amplitudes and
phases of the sinusoids are all that is needed to specify the Fourier series expansion. Musical
signals are a natural application of Fourier series, since musical signals (specifically, an
instrument playing a specific note) are periodic. The sinusoid with the same period as the music
signal is called the fundamental; it is the pure tone that sounds most like the signal. To obtain
the richer sound of an instrument playing a note, we add in harmonics; musicians call them
overtones. Harmonics are sinusoids at frequencies double, triple, etc. the frequency of the
fundamental. The amplitudes of the harmonics determine the timbre (sound) of the instrument
playing the note. The reason a violin playing note B sounds different from a trumpet playing
note B is that the amplitudes of the harmonics are different.
The Fourier series representation of a musical signal is specified by only a few numbers (the
amplitudes and phases of the harmonics, and the note):
∞ ∞ () = ∑ { ejω0 kt e−j } = ∑ cos(0 − ) In practice, the infinite series is truncated to a finite number (k) of terms, giving a finite Fourier
series. Finite Fourier series still give good approximations to most periodic signals.
Since instruments playing musical notes create periodic signals, musical signals have Fourier
series expansions. The Fourier series can be truncated to a finite number of terms and still do a
good job of representing the musical signal. The timbre (sound) of the trumpet is produced by
the amplitudes Ak. The fundamental frequency alone would be a pure tone; the overtones
(harmonics) create the richer sound of the trumpet.
Here is a table of Ak and values for nine harmonics:
Harmonic 1 (fundamental)
2
3
4
5
6
7
8
9 - Relative Amplitude 0.1155
0.3417
0.1789
0.1232
0.0678
0.0473
0.0260
0.0045
0.0020 - Relative Phase in Radians -2.1299
+1.6727
-2.5454
+0.6607
-2.0390
+2.1597
-1.0467
+1.8581
-2.3925 Suppose the maximum frequency in the Bach Fugue is 1200 Hz.What is the minimum sampling
frequency needed to synthesize, without aliasing, a trumpet sound containing nine harmonics? EEL3135: Intro to Signals & Systems 9 Lab 3: Music Synthesis withSinusoidal Signals Barukh Rohde University of Florida Fall 2016 Using a sampling frequency of 44100 Hz, construct your Bach Fugue in trumpet. Submit this
as a .wav file on Canvas.
Don’t forget to submit your PDF file, too!
2.9001 Extra Credit – Synthesize a Musical Piece of your own!
For up to fifteen points of extra credit, out of 100 for the entire lab, synthesize a piece of music
into a structure of theVoicesform, calling it theVoices_yourname. Save it as
yourname_fugue.mat. Submit the .mat file, your .m code, your PDF explaining it, and the
.wav of your musical composition. A simple composition might get 5 points. A more complex
one might get 10. A really well-done one might earn the full 15 points. Again, be creative!
Some ideas:
How might you create a beat using MATLAB? The Internet has the answer for you.Some
melodies are best played using a trumpet. Others might do better with a piano-sounding set of
harmonics and envelopes, or a flute-sounding set of harmonics and envelopes.
We look forward to hear your compositions! EEL3135: Intro to Signals & Systems 10 Lab 3: Music Synthesis withSinusoidal Signals

 


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