INQ 241A

Lab 21: Sounds

Practice Problem 1

Write a function called average_list(a_list), which takes a list of integers as a parameter. Your function should print the average of the input grades.

Example

>>> average_list([0, 1, 2])
1.0
>>> average_list([1, 1, 1, 1, 1, 1])
1.0
>>> average_list([2, 4, 6, 8])
5.0

Hint

Practice Problem 2

Write a function called print_evens(a_list), which takes as a parameter a list of integers. Your function should print only the even values in the list.

Example

>>> print_evens([0, 1, 2, 3, 4, 5])
0
2
4
>>> print_evens([2, 1, 2, 3, 2, 4, 2])
2
2
2
4
2
>>> print_evens([1, 3, 4, 7, 9, 11, 13])
>>>

Hint

Lists are similar to Strings, as far as Python is concerned. We can use a for loop to iterate over the items of our list. for item in a_list

You can check to see if a number $x$ is even if x % 2 == 0

Reverse Sound

In a file called reverse_sound.py write a function called reverse(a_sound). This function should modify the passed in sound to play backwards.

Example

Before

Nato Phonetic Alphabet Normal

After

Nato Phonetic Alphabet Reversed

Hint

Sounds are represented as a collection of samples. This collection of samples can be thought of as a list, which you can leverage in order to reverse the order of the samples.

You can get the number of samples in a file by using the getNumSamples(a_sound) function. This returns a floating point number, so you may need to convert it to an integer before you use it. You can use the int function for that.

The getSamples(a_sound) function gives you a list of the samples from the sound. You need to store this in a variable, as it will be very useful later.

To get the value of a specific sample of the sound, you can use the getSampleValue(sample) function. This is very similar to getRed(pixel) for images.

In this case, your sound has some duration $d$ . for the $i^{th}$ sample in your reversed sound, you want to get the sample at index $d - i - 1$ .

To set the sample value for your sound, you use the setSampleValue(sample, value) function. This is like the setRedValue(pixel, color) function for images.