Ever wonder what is inside an Ipod?

1
Ever wonder what is inside an Ipod?
2
Inside an Ipod
Battery
Hard Drive
Digital Signal Processors
Flex Circuit
Analog and Digital Board Design
Flash Memory
3
Inside an Ipod
Electrical Circuits (2122)
Fundamentals of EE (1382)
Intro to DSP (3372)
Circuit Analysis (2350)
Digital Computer Logic (2381)
4
Ways to Make Music

• All systems that make music
• Have a musical source
• Have a way to read music information
• Convert musical information to sound
• Create sound waves in air

• The result A sound signal - but what is it?

5
Signals are Everywhere

• Signal A pattern or variation that contains
  information

6
Sound Signals

• Sound Signal A pattern or variation in molecules
  that a sound makes
• Sound has a speed that is different for different
  materials

7
Whats the difference between wind and sound?
Wind
8
Whats the difference between wind and sound?
Sound
9
Whats the difference between wind and sound?
Sound
10
Whats the difference between wind and sound?
Sound
11
Whats the difference between wind and sound?
Sound
12
Whats the difference between wind and sound?
Sound
13
Whats the difference between wind and sound?
Sound
14
Whats the difference between wind and sound?
Sound
15
Whats the difference between wind and sound?
Sound
16
Whats the difference between wind and sound?
Sound
17
Whats the difference between wind and sound?
Sound
18
Whats the difference between wind and sound?
Sound
19
Whats the difference between wind and sound?
Sound
20
Whats the difference between wind and sound?
Sound
21
Whats the difference between wind and sound?
Sound
22
Whats the difference between wind and sound?
Sound
23
Whats the difference between wind and sound?
Sound
24
Whats the difference between wind and sound?
Sound
25
Whats the difference between wind and sound?
Sound
26
Whats the difference between wind and sound?
Sound
27
Whats the difference between wind and sound?
Sound
28
Whats the difference between wind and sound?
Sound
29
Whats the difference between wind and sound?
Sound
30
Whats the difference between wind and sound?
Sound
31
Whats the difference between wind and sound?
Sound
32
Whats the difference between wind and sound?
Sound
33
Whats the difference between wind and sound?
Sound
34
Making Sounds Using Signals

• Amazing Fact Any sound can be created, stored,
  and played using signals!
• Microphones and loudspeakers enable us to record
  and play sounds
• We only need one signal to represent any sound

35
Pitch and Fundamental Frequency

• Pitch how high or low a periodic signal sounds.
  Can we be more precise?
• Yes! Use fundamental frequency, given by f
  1/T
• Units of frequency cycles per second or Hertz
  (Hz)

36
Problem Fundamental Frequency and Period

• Determine the fundamental frequencies of the
  sounds shown

Solution Both have periods of 0.0038 sec.
Therefore, f1/0.0038 f 263Hz (middle C)
37
1
38
5
39
6
40
7
41
8
42
9
43
10
44
11
45
12
46
13
47
14
48
15
49
16
50
17
51
18
52
19
53
20
54
21
55
22
56
23
57
24
58
25
59
Manipulating Signals

• Three musically-useful ways
• Amplitude scaling Changing its height x(t)
  A s(t)
• Time shifting Moving left or right y(t)
  s(t d)
• Time scaling Stretching or shrinking the time
  axis z(t) s(c t)

60
Exercise Plotting Signals

• Plot the signals s(t) 2 t 3
• s(t) 0.3 cos(3 t)
• s(t) 6 t2 - 4

• Which one of these looks like a musical signal?

61
Example Problem Adding Two Signals Together
time (sec)
time (sec)
62
Example Problem Solution
63
Example Adding Two Sinusoids Together

• This problem is hard to do by hand
• but easy to do digitally!

64
Musical Signals and Period

• Observation The simplest musical signals are
  periodic they have shapes that repeat
• Period The repeating interval T of a periodic
  signal in units of time (seconds, milliseconds.)
• For any periodic signal p(t), p(t) p(t T).

Example T 0.0038 sec 3.8 msec
65
A Little Musical Notation
The y-axis is frequency
The x-axis is time

• Each note on a page of sheet music corresponds to
  a signal with a particular frequency and duration

66
The Key to Reading Music

• When a musical score is played, each note becomes
  a signal with a fundamental frequency

• The type of note determines its duration

67
Making Musical Sounds

• Signals that have a pitch are periodic
• A periodic signal repeats over and over
• Therefore, to make a single note from a musical
  instrument, we need to create one period of its
  sound and play it over and over.

68
Our First Digital Band Design
69
Refining the Design

• How do we get the musical information to our
  digital band?
• How do we specify each instruments signal shape?
• How do we make several instrument sounds and play
  them simultaneously?

70
Specifying the Musical Score

• Traditionally, music has been written on paper
• Portable and easy for humans to read
• Destructible and a little hard for digital
  devices to read
• Is there a more convenient format for our musical
  information?

71
Musical Instrument Digital Interface
(MIDI)

• MIDI specifies (a) note on/off time stamps and
  (b) note frequencies
• Convenient digital format
• A standard in widespread use

72
Specifying the Shape of the Musical Instrument
Sound

• Most musical instrument signals have complicated
  shapes
• We shall start with simple periodic signals -
  the sine and cosine functions

73
Turning a Sine or Cosine into a Sinusoid

• To make a sound from a sine or cosine function,
  make the angle a function of time
• s(t) A cos(2 p t / T) angle units
  radians
• A Amplitude , T Period
• Can show s(t) s(t T) is periodic

People cant hear the difference between
sines and cosines!
Example A 3.1 T 2.5 msec
74
Making Simple Melodies
75
Our Second Digital Band Design

• How do we extend this
• system to play
• Different
• instruments?
• (b) Multiple notes simultaneously?

This system allows us to play simple
single-note melodies with a simple (sinusoidal)
instrument sound.
76
Making More than One Note at a Time

• To play two notes simultaneously, add their
  signals together

77
A
A-
B
B
B-
C
C
C-
D/F