COSC 1P02

Introduction to Computer Science 5.1

Cosc 1P02Week 5 Lecture slides

Psychiatrist to patient "You have nothing to worry about - anyone who can pay my bill is certainly not a failure."

COSC 1P02

Introduction to Computer Science 5.2

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

COSC 1P02

Introduction to Computer Science 5.3

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)

COSC 1P02

Introduction to Computer Science 5.6

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

COSC 1P02

Introduction to Computer Science 5.8

Mirroring A Sound

Mirror around mid-point odd vs even number of samples

Copying sample values only half copied can’t use for-each

Indexing a collection aSound.getSample(i)

returns Sample at position (index) i in sound positions start at 0 (last position numSamples-1)

Example mid point uses counting for from position & to position

for each vs for & indexing

COSC 1P02

Introduction to Computer Science 5.9

Reversing a Sound Produce a new sound which is the old sound in reverse order

like mirror except all samples reproduced in reverse order

create a new Sound object Example

Sound objects now declared in method more than one sound involved must be passed as parameter (scope)

Creating a new sound with same attributes Sound constructor

Cascading method calls aSound.getSample(i) returns a Sample object this object can perform the getValue() method saves declaring a variable that isn’t going to be used

except to make next call

COSC 1P02

Introduction to Computer Science 5.10

Function Methods Methods can produce a result

value (e.g. sin()) object (e.g. getSample())

Method declaration void – procedure method

no result executed for its effect

type – function method result is of specified type executed for result

Method call procedure method

called as a statement (e.g. close()) function method

called as an expression (e.g. sin())

COSC 1P02

Introduction to Computer Science 5.11

Method execution

value of argument computed calling code suspended value of argument copied to parameter body of method executed functions: return “value” computed calling code continues (functions: with return “value”)

Return statement syntax execution

expression computed method terminates (returns)

COSC 1P02

Introduction to Computer Science 5.12

Changing the Frequency of a Sound

Change pitch by changing frequency e.g. A above middle C is 440Hz, next A is 880Hz

To double frequency must halve cycle length if sampling rate is constant, there will be half as many

samples in the higher frequency version of the same sound Select every other sample to create a new sound

same rough shape but compressed (higher frequency) new sound will be half as long (half as many samples)

Example new sound has half the samples need a value for each sample in result (for-each) every other sample of old sound

pos has values: 0, 2, 4, …

COSC 1P02

Introduction to Computer Science 5.14

Combining Sounds

When two sounds occur together, their sound waves merge e.g. instruments in an orchestra merging is just addition of the samples at the same point in

time What if one sound is longer than the other

merging occurs over duration of shorter sound result has tail end of longer sound

Example determine longer & shorter sound result has length of longer sound merge as many samples as in shorter sound to maintain volume, use half the amplitude of each sample copy tail of longer sound

Note: for loop index doesn’t have to start at 0 or 1

COSC 1P02

Introduction to Computer Science 5.15

SoundPlayer Methods

method meaning close() wait until user presses Close button and

close window placeSound(sound) make sound playable when pressing the Play

button waitForUser() Wait until user presses OK before continuing

COSC 1P02

Introduction to Computer Science 5.16

Sound Methods

method meaning o = new Sound() constructor: creates a sound object loading samples from a

file selected via a file open dialog o = new Sound(nSamp) constructor: creates a sound object with nSamp samples

all 0 (silence). o = new Sound(nSamp,sound) constructor: creates a sound object with nSamp samples

all 0 (silence) and attributes of sound. i = getNumSamples() returns number of samples in the sound s = getSample(pos) returns the Sample at position pos in the sound i = getSampleRate() returns to sampling rate of the sound (samples/second) save() present file save dialog to allow user to save sound as

modified

COSC 1P02

Introduction to Computer Science 5.17

Sample Methods

method meaning i = getValue() returns the value (amplitude) of the sample setValue(amp) changes the value of the sample to amp

COSC 1P02

Introduction to Computer Science 5.18

The end