Chapter 2: Creating Digital Music Outline

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    •  After finishing this chapter you are responsible for being able to describe, define, and compare these concepts:
    LabVIEW LAB OBJECTIVES
    A. FIRST Engineering Problem: Create digital music using LabVIEW block functions. These are the Chapter 2 Labs (L2.x).

               1. Understand first hand how working with block diagrams allows one to make simple blocks do complex things.
                 2. Manipulate and control the parameters of blocks within worksheets
                 3. Any LabVIEW labs modified or altered in lab and saved to your flash drive will be uploaded to the Google Groups for our class and named according to the standard convention.

    a. Connect blocks by locating input and output links on blocks

    b. Change block properties through the use of right mouse

    c. Show an ability to do basic trouble shooting on the DSK board setup and cabling.
    B. Know and distinguish between the various methods of creating digital music:
                1. Sound Synthesis
                2. Waveform Synthesis
                3.     Physical Modeling
    C. Be able to:

    1.  Distinguish between analog and digital signals. Give a simple analog signal and a sample rate, be able to create a digital signal. Know the difference in the signal notation for each: s(t) vs. s[n]

    2.    Given a simple periodic waveform, be able to write the appropriate sinusoid equation to represent the amplitude, frequency, and phase shift of the signal as a function of time.

    3.    Create a graphical representation of a digital or an analog signal if the equation is given.

    4.     Distinguish between tones that vary in amplitude or period or frequency.
    D. Make sure you check out these Acoustic Simulations and the Phasor Factory for additive synthesis before the test.
    E. SECOND Engineering Problem: Build a functioning Gosney speaker/ microphone.

    DIGITAL MUSIC CONTENT OBJECTIVES
    1.  What are the characteristics of sound?   
    a. Sound in matter: what are compression waves and how are they measured? 
    b.  How is a transverse wave different from sound?
    > Wave modeling site
    2.  Describe the parts of the ear, their function and sequence in processing sound:
    a. outer ear (role of pinnae)
    b. middle ear (eardrum, stapes, malleus, incus bones; Eustachian tube)
    c. inner ear (cochlea (oval window, basilar membrane, fluid, sensor cells, nerves, round window) and semicircular canals (how do they allow balance?)).
    > Ear Physiology illustrations and descriptions
     
    3.  Reason for human hearing range
    a. The Cochlea's basilar membrane resonant frequency changes from 20 Hz  -20 kHz  based on logarithmic changes in its thickness.
    b. Movement of a particular section of the membrane causes the attached sensory cells to sway and induce a depolarization of the nerve fibers assigned to those cells. 
    c. Depending on which section of the basilar membrane responds, geographically precise signals are assigned different frequencies in the brain.
    d. frequencies below 20 Hz (infrasound) have no advantages to human communication and natural sources of these sounds could "swamp" the auditory centers of the brain.
     
    4. lambda = c/f or wavelength = speed /frequency
     
    5.  Decibel scale basics
    a. approximately every 6 dB change is a doubling of the amplitude of the signal.
     
    6. Waveform Synthesis- the simplest method
    a. Using a single period from a real instrument sound, make periodic signals or p(t) at different frequencies to create a range of notes.
    b. Copy, Time Warp the p(t) to get a new frequency, and Repeat the process for a new note
    7. Additive Synthesis- rely upon multiple sinusoids added together to recreate any complex p(t)
    a. Fourier Analysis can break down any p(t) into sinusoid components that can be added back together to recreate the original sound. See basic wave forms decomposed in this java applet.
    b. Banks of sinusoid generators, or oscillators, were what gave the old '60's synthesizers their unique sounds.
    c. Sound envelope (attack, decay, sustain, release or ADSR) shaping
    8. Physical modeling of sounds- what is it? What is its usefulness?
    a. Using the vast computational power of modern computers to recreate the energy transfers between strings/fingers or air/lips and the instrument itself in order to more closely mimic reality. Stringed instruments are easier to model than wind instruments due to the issue of turbulence (chaotic air flow).
    b.

    Modeling the above using standing & traveling wave equations, energy transfer, harmonic frequencies
            > variables of speed, mass, tension, mass per unit, restoration coefficients in stringed instruments (see #13 objective)
    c. Role of buffers & delay elements in the guitar model
    d. Much more complicated and realistic way of making a digital instrument.
            > Uses all of the tools that the physics of moving fluids has to offer for woodwinds or the human voice
           >Creating a vocal orchestration via digital simulation- the ultimate karoake machine.

    e. Objectives #10- 15 relate to this process.
    9. Identify the unique envelopes (visual and auditory) for these instruments:
    a. guitars- plucked
    b. violins- bowed
    b. pianos
    c. clarinets

    The following are in supplementary reading packets or in web tutorials:

    10. What are the characteristics of harmonic oscillators?
    a. Disturbance caused by a displacement leads to a return to equilibrium. Kinetic energy changes to potential energy and back again.
    b. The amount of restorative force is proportional to the amount of displacement.
    c. The period & frequency of the oscillator is independent of the amplitude.
    d. The period & frequency of the oscillator are dependent upon the mass and stiffness of the restorative forces (both of which are a function of the length).
     
    11. What is resonant energy transfer? What role does this play in the engineering design of:
    a. guitars/violins
    b. pianos/harpsichords
    c. pipe organs
    d. buildings
    e. aircraft wings
     
    12. Harmonics- how does creating the first, second, third, etc. harmonics change the frequencies heard? 
    a. What is an octave?
    b. What frequency arrangements are used in Western music (thanks to the Pythagoreans!)?
    > A different way of analyzing chord structures using visual diagrams can be found at the "Shape of a Song". Look at some of the examples.
    13. Pipe organs vs. Stringed instruments  
    a. Which has more vibrational modes? Which must have at least an antinode at one "end" of the oscillator?
    b. How does a pipe open at both ends sound different from a pipe closed at one end?
    c. What is oscillating in a pipe organ? Why?
    d. Why does a concert A (440 Hz) sound different when played on a pipe organ vs. a stringed instrument? How would they look on the "freq" display after a Fourier transform?
    e. How does length correspond to frequency in both types of instruments?

    The following are from lab work and reading packets:

    14. How can echo & reverb (fast echo) be modeled using the physics of sound? 
    a. secho(t) =decay alpha*s(t-Tdelay)
    b. how do you model an echo digitally?
     
    15. Sound capture or sound production by speaker/microphones attached to the DSK- how do these basically function in analog and digital terms?
     
    16. How do speakers (like the Gosney Speaker) work?
    a. How is light (electromagnetic field- EM) fundamentally different from sound?
    b. How can induced electrical currents occur in a copper coil in the presence of an accelerating magnet? How can the reverse also happen?
    c. How does "b" above relate to the engineering of speakers/microphones?
    d. Describe the sequence that occurs from the moment a sound wave hits a microphone until that sound is amplified out of a speaker. Include as many specific Chapter 3 terms as you can.
     
    17. How is this link between electricity and magnetism used to make an electric guitar? What are the advantages/disadvantages of an analog electric or digital instrument?
    > See how Carlos Santanna's electric guitar functions
     

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