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COSC 1P02 Cosc 1P02 Week 5 Lecture slides Psychiatrist to patient "You have nothing to worry about - anyone who can pay my bill is certainly not a failure." Introduction to Computer Science 5.1 COSC 1P02 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 Introduction to Computer Science 5.2 COSC 1P02 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) Introduction to Computer Science 5.3 COSC 1P02 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 Introduction to Computer Science 5.6 COSC 1P02 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 Introduction to Computer Science 5.8 COSC 1P02 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 Introduction to Computer Science 5.9 COSC 1P02 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()) Introduction to Computer Science 5.10 COSC 1P02 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) Introduction to Computer Science 5.11 COSC 1P02 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, … Introduction to Computer Science 5.12 COSC 1P02 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 Introduction to Computer Science 5.14 COSC 1P02 SoundPlayer Methods method close() placeSound(sound) waitForUser() meaning wait until user presses Close button and close window make sound playable when pressing the Play button Wait until user presses OK before continuing Introduction to Computer Science 5.15 COSC 1P02 Sound Methods method o = new Sound() o = new Sound(nSamp) o = new Sound(nSamp,sound) i = getNumSamples() s = getSample(pos) i = getSampleRate() save() meaning constructor: creates a sound object loading samples from a file selected via a file open dialog constructor: creates a sound object with nSamp samples all 0 (silence). constructor: creates a sound object with nSamp samples all 0 (silence) and attributes of sound. returns number of samples in the sound returns the Sample at position pos in the sound returns to sampling rate of the sound (samples/second) present file save dialog to allow user to save sound as modified Introduction to Computer Science 5.16 COSC 1P02 Sample Methods method i = getValue() setValue(amp) meaning returns the value (amplitude) of the sample changes the value of the sample to amp Introduction to Computer Science 5.17 COSC 1P02 The end Introduction to Computer Science 5.18
