cosc 1p02 introduction to computer science 4.1 cosc 1p02 week 4 lecture slides “programs are meant...

COSC 1P02

Introduction to Computer Science 4.1

Cosc 1P02

Week 4 Lecture slides

“Programs are meant to be read by humans and only incidentally for computers to execute.”- Donald Knuth

COSC 1P02


Sound

Waves of air pressure increases in pressure (wave) called compressions decreases in pressure (toughs) called rarefactions

Sound perceived based on shape, frequency and amplitude of wave

Sine wave simplest sound (regular) cycle amplitude Frequency

COSC 1P02


Volume

we hear changes in intensity (amplitude) Change (ratio) measured in decibels (dB) Commonly volume expressed in dB as ratio to threshold

of audibility (0 dB SPL) normal speech: 60 dB SPL shouting: 80 db SPL Based on a logarithmic scale

10 db is 10x louder then 0 (silence) 20 db is 100x louder then 0 (silence) 30 db is 1000x louder etc….

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Pitch/Tone

All sounds are periodic have cycles

Frequency is the number of cycles per second (measures in Hertz (Hz))

the A above middle C is 440Hz we can hear from 2Hz to 22,000 Hz (or 22 kHz)

we hear pitch as the change in frequency in standard tuning ratio of notes in neighboring

octaves is 2:1 (e.g. 440Hz : 880Hz) ratio of notes in different octaves remains constant

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Shape

Different sources of sound - sound different even when playing the same note

e.g. flute vs piano Sounds seldom have a single frequency

overtones are other frequencies in the sound that are at lower amplitude

The central tone is called the fundamental tone Sounds also vary by attack, fade and other characteristics

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Exploring Sounds

SoundInspector tool Java program built using the BasicIO & Media libraries draws sound wave and allows zooming in on parts of

wave E.g

c4.wav – sine wave - middle C e4.wav – sine wave – E above C bassoon-c4.wav – bassoon playing middle C rabbit.wav thisisatest.wav

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Encoding (Digitizing) Sounds

Microphone measures air (sound) pressure record voltage (analog) as a number (digital) – analog-

to-digital conversion (ADC) Sound is change of air pressure over time

record samples of air pressure over time Number of samples?

depends on highest frequency to capture Nyquist’s theorem – to capture frequencies up to n Hz

must have 2n samples per second to handle 22,000 Hz need 44,000 samples per

second CDs are sampled at 44,100 samples per second

Sample size CDs use 2 bytes (16 bits) per sample

65,536 (216) possible values (-32,768 to 32,767) Note: 80 min @ 44,100 samples per second at 2 bytes per

sample x 2 channels (stereo) = 846,720,000 bytes or approximately 800 Mb

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Sound & SoundPlayer

Sound class in the Media library provides access to sounds sounds can be loaded from files (.wav)

SoundPlayer class in the BasicIO library provides a window with a button to play a sound Sound objects placed on SoundPlayer

Example Load and play a sound

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Making a Sound Louder

Increase amplitude of each sample multiply each by some factor (parameter of a method)

Example Sequence through all samples in sound

Sample class for each executes body once for each Sample in the Sound

index variable (now a Sample) is each Sample in succession

Saving the result Did it work?

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Generating Clipping

Clipping occurs when the sample value exceeds the maximum sample size (e.g. greater than 32,767 or less than -32,768 for a 2 byte sample).

sample value when clipped will be the maximum value (32,767 or -32,768)

If keep increasing volume, clipping occurs What happens if all samples clipped? Example

program to set all samples to maximum value What does signal look like? Note: we can still understand it! if statement

choice between executing two alternatives to handle maximum positive and maximum negative

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If Statement

Syntax If condition is true, the first set of statements (then part)

is executed, otherwise the second set of statements (else part) is executed

Condition an expression that is either true or false relational operators note: also used in for statement (second part)

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Normalizing a Sound What if we want to make a sound as loud as we can without causing

clipping? Need to know the largest (absolute value) amplitude (sample) Can scale each sample by the ratio of this largest value to the

maximum sample size (32,767) Finding maximum

sequence through all samples and if find one that is bigger than the biggest so far, change our guess of what the biggest value is

work with absolute value (i.e. don’t care if positive or negative) need a starting guess

since looking at absolute value, no sample can be smaller than 0 so 0 can be starting guess

Example Note: need two loops

one to find maximum one to scale samples

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cosc 1p02 introduction to computer science 4.1 cosc 1p02 week 4 lecture slides “programs are meant...

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