COSC 1P02 Introduction to Computer Science 5.1 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."

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 5.13

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

COSC 1P02 Introduction to Computer Science 5.16 Sound Methods

COSC 1P02 Introduction to Computer Science 5.17 Sample Methods

COSC 1P02 Introduction to Computer Science 5.18 The end