WAV audio file handling in SciPy - Mini Project: Build & Apply

WAV Audio File Handling with SciPy

📖 Scenario: You have recorded a short sound clip and saved it as a WAV audio file. You want to analyze this audio file by loading it into your program, checking its properties, and then extracting some useful information.

🎯 Goal: Learn how to load a WAV audio file using SciPy, check its sample rate and data shape, and extract the first 100 audio samples.

📋 What You'll Learn

Use SciPy's wavfile module to read WAV files

Access the sample rate and audio data from the file

Extract a slice of the audio data

Print the sample rate and the extracted audio samples

💡 Why This Matters

🌍 Real World

Audio processing is common in music apps, voice assistants, and sound analysis tools. Loading and inspecting WAV files is the first step in these tasks.

💼 Career

Understanding how to handle audio files is useful for data scientists working in audio analytics, speech recognition, and multimedia applications.

1

Load the WAV audio file

Write code to import wavfile from scipy.io and read the WAV file named example.wav using wavfile.read. Store the sample rate in a variable called sample_rate and the audio data in a variable called audio_data.

SciPy

# Import wavfile and read 'example.wav' to get sample_rate and audio_data
# Your code here

Hint

Use from scipy.io import wavfile to import the module. Then use wavfile.read('example.wav') to read the file.

2

Check the sample rate and audio data shape

Write code to create two variables: rate that stores the value of sample_rate, and shape that stores the shape of audio_data using its shape attribute.

SciPy

from scipy.io import wavfile
sample_rate, audio_data = wavfile.read('example.wav')
# Create variables rate and shape from sample_rate and audio_data.shape
# Your code here

Hint

Assign rate = sample_rate and shape = audio_data.shape.

3

Extract the first 100 audio samples

Write code to create a variable called first_100_samples that contains the first 100 elements of audio_data using slicing.

SciPy

from scipy.io import wavfile
sample_rate, audio_data = wavfile.read('example.wav')
rate = sample_rate
shape = audio_data.shape
# Extract the first 100 samples from audio_data into first_100_samples
# Your code here

Hint

Use slicing like audio_data[:100] to get the first 100 samples.

4

Print the sample rate and first 100 samples

Write code to print the sample rate stored in rate and the first 100 audio samples stored in first_100_samples. Use two separate print statements.

SciPy

from scipy.io import wavfile
sample_rate, audio_data = wavfile.read('example.wav')
rate = sample_rate
shape = audio_data.shape
first_100_samples = audio_data[:100]
# Print the sample rate and first 100 samples
# Your code here

Hint

Use print(rate) and print(first_100_samples) to display the 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