WAV audio file handling in SciPy - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read a WAV file using scipy.

SciPy

from scipy.io import wavfile
sample_rate, data = wavfile.[1]('audio.wav')

Drag options to blanks, or click blank then click option'

Aread

Bload

Cwrite

Dopen

Attempts:

3 left

💡 Hint

Common Mistakes

Using wavfile.write instead of wavfile.read

Trying to use wavfile.load which does not exist

The wavfile.read function reads a WAV file and returns the sample rate and data array.

2fill in blank

medium

Complete the code to write data to a WAV file using scipy.

SciPy

from scipy.io import wavfile
wavfile.[1]('output.wav', sample_rate, data)

Drag options to blanks, or click blank then click option'

Awrite

Bread

Csave

Dexport

Attempts:

3 left

💡 Hint

Common Mistakes

Using wavfile.read instead of wavfile.write

Trying to use wavfile.save which does not exist

The wavfile.write function saves audio data to a WAV file with a given sample rate.

3fill in blank

hard

Fix the error in the code to correctly read a WAV file and print its sample rate.

SciPy

from scipy.io import wavfile
sample_rate, data = wavfile.read('sound.wav')
print([1])

Drag options to blanks, or click blank then click option'

Adata

Bsample_rate

Cwavfile

Dsound.wav

Attempts:

3 left

💡 Hint

Common Mistakes

Printing the data array instead of sample rate

Printing the filename string instead of a variable

To print the sample rate, use the variable sample_rate which stores it after reading the file.

4fill in blank

hard

Fill both blanks to create a dictionary with word lengths for words longer than 3 letters.

SciPy

words = ['sound', 'wav', 'file', 'data', 'io']
lengths = {word: [1] for word in words if len(word) [2] 3}

Drag options to blanks, or click blank then click option'

Alen(word)

B>

C<

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using the word itself instead of its length

Using less than < instead of greater than >

This dictionary comprehension stores the length of each word only if the word length is greater than 3.

5fill in blank

hard

Fill all three blanks to create a dictionary with uppercase keys and values filtered by positive numbers.

SciPy

data = {'a': 1, 'b': -2, 'c': 3}
result = { [1]: [2] for k, v in data.items() if v [3] 0 }

Drag options to blanks, or click blank then click option'

Ak.upper()

Bv

C>

Dk

Attempts:

3 left

💡 Hint

Common Mistakes

Using original keys instead of uppercase

Including negative values by mistake

This dictionary comprehension creates keys as uppercase letters and includes only items with positive values.

Practice

1. What does the function scipy.io.wavfile.read return when you load a WAV audio file?

easy

A. The file size and duration

B. Only the audio data as a list

C. The sample rate and the audio data as a NumPy array

D. The audio format and bit depth

Solution

1. Step 1: Understand the function purpose

   scipy.io.wavfile.read is designed to load WAV files and extract audio information.

2. Step 2: Identify the returned values

   It returns two things: the sample rate (how many samples per second) and the audio data as a NumPy array.

3. Final Answer:

   The sample rate and the audio data as a NumPy array -> Option C

4. Quick Check:

   read() returns (rate, data) [OK]

Hint: Remember read() gives rate and data array [OK]

Common Mistakes:

• Thinking it returns only audio data
• Confusing sample rate with file size
• Expecting metadata like format or bit depth

2. Which of the following is the correct way to import the WAV file reading function from scipy?

easy

A. from scipy.io import wavfile

B. import scipy.wavfile.read

C. from scipy import wavfile.read

D. import wavfile from scipy.io

Solution

1. Step 1: Recall correct import syntax

   Python imports use 'from module import function_or_submodule' format.

2. Step 2: Match with scipy structure

   The correct way is to import the wavfile submodule from scipy.io as from scipy.io import wavfile.

3. Final Answer:

   from scipy.io import wavfile -> Option A

4. Quick Check:

   Correct import syntax = from scipy.io import wavfile [OK]

Hint: Use 'from scipy.io import wavfile' to access read/write [OK]

Common Mistakes:

• Trying to import read directly
• Using dot notation incorrectly in import
• Swapping import order

3. What will be the output shape of the data array when you read a stereo WAV file with 44100 samples per channel using scipy.io.wavfile.read?

medium

A. (88200,)

B. (44100, 2)

C. (44100,)

D. (2, 44100)

Solution

1. Step 1: Understand stereo audio data shape

   Stereo audio has two channels, so data shape is (samples, channels).

2. Step 2: Calculate shape for 44100 samples

   With 44100 samples per channel and 2 channels, shape is (44100, 2).

3. Final Answer:

   (44100, 2) -> Option B

4. Quick Check:

   Stereo shape = (samples, 2) [OK]

Hint: Stereo data shape is (samples, 2) always [OK]

Common Mistakes:

• Confusing channels and samples order
• Assuming shape is (2, samples)
• Thinking stereo data is flattened

4. You try to save a NumPy array with float values using scipy.io.wavfile.write but get an error. What is the likely cause?

medium

A. The file path is incorrect

B. The sample rate is missing

C. The array shape is (samples, 2) instead of (2, samples)

D. The array must be integer type, not float

Solution

1. Step 1: Check data type requirements for write()

   scipy.io.wavfile.write expects integer arrays (e.g., int16) for audio data.

2. Step 2: Identify error cause

   Using float arrays causes errors because WAV format stores integers, so conversion is needed.

3. Final Answer:

   The array must be integer type, not float -> Option D

4. Quick Check:

   write() needs int arrays [OK]

Hint: Convert floats to int before writing WAV [OK]

Common Mistakes:

• Ignoring data type and writing floats directly
• Forgetting sample rate argument
• Misunderstanding array shape requirements

5. You want to double the speed of a WAV audio file using scipy.io.wavfile. Which approach correctly achieves this?

hard

A. Double the sample rate value and write the original data unchanged

B. Read the file, then write only every second sample to a new file

C. Halve the sample rate value and write the original data unchanged

D. Reverse the audio data array and write it with the original sample rate

Solution

1. Step 1: Understand speed and sample rate relation

   Speed changes by adjusting sample rate: doubling sample rate doubles playback speed.

2. Step 2: Apply correct method

   Keep audio data unchanged but write with double the original sample rate to speed up playback.

3. Final Answer:

   Double the sample rate value and write the original data unchanged -> Option A

4. Quick Check:

   Speed ∝ sample rate, double rate doubles speed [OK]

Hint: Change sample rate to speed up audio, not data length [OK]

Common Mistakes:

• Skipping samples instead of changing sample rate
• Halving sample rate to speed up (actually slows down)
• Reversing data does not change speed