```python
'''
Document containing functions to edit audio
'''
import scipy.io.wavfile as spw

def make_quiet(filename):
  '''
  Lowers the volume of WAV file to a quarter of the original 
  volume
  Parameters:
      filename - the name of a WAV file 
  Returns:
      A new WAV file that is a quarter of the original volume
  '''
  try:    
    sample=spw.read(filename)
    LOWER_VOLUME=4
    for i in range(len(sample[1])):
      sample[1][i]=sample[1][i]//LOWER_VOLUME
    spw.write('quieter.wav', 44100, sample[1])
  except IOError:
    print('Incorrect filename, please try again')
```





Davidson College

When thinking of WAV files, you can imagine them to be a long list of sound wave amplitude measurements. The length of this list correlates with the sample rate (samples/sec) and then the file length (sec). So, a 2 second WAV file that contains data sampled at 44,100 samples/sec has 88,400 amplitude measurements stored in a list. 

The SciPy library allows us to easily access this data by using the scipy.io package. To start, let's just try to see the audio data using SciPy.
```python
import scipy.io.wavefile as spw
##I now will use my read function to open chicken.wav
sample=spw.read('chicken.wav')
print(sample)
```
This should print the following to the console:
```python
(44100, array([ 54,  66,  70, ..., -34, -31, -28], dtype=int16))
```
As you can see, the ```read``` function returns the sample rate, the data as an array, and labels the data type. Thus, we have a WAV file sampled at 44,100 samples/sec, represented as an array containing integers. 

What if we just wanted to grab the data in the array? It looks like the variable ```sample``` is a tuple containing the list we want as the second element. Thus, we can use indexing. 
```python
print(sample[1][0])
```
This should print the following to the console:
```python
54
```
Now that we have established how SciPy allows us to make WAV file data explicit, we can explore ways to manipulate this data. 

Basics of Audio Editing using SciPy File I/O

Audio Editing with SciPy Full Example

Now that we understand that SciPy File IO lets us interact with WAV files as lists of frequencies, we can start to think of ways to manipulate this data to create recognizable effects. 

-Change volume: If we want to make a WAV file quieter or louder, we could create a loop that iterates for each element in the WAV file frequency list and replaces each original element by multiplying the original element by a constant. The constant should be less than 1 to quiet the WAV file, and greater than one to make the file louder.

-Slow down: If we want to make a WAV file with a slowed down effect we could create a loop that iterates for each element in the WAV file frequency list and doubles the original elements consecutively. The resulting file would be twice as long and thus slower. 

-Reverse audio: If we want to reverse a WAV file, create a loop that reverses the order of the elements in the list

As you can see, these ideas are pretty intuitive. How can we create effects that are less intuitive, such as a record skipping effect?

Learn Before

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