WAV audio file handling in SciPy - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of reading WAV file sample rate

What is the output of this code snippet that reads a WAV file's sample rate?

SciPy

from scipy.io import wavfile
sample_rate, data = wavfile.read('example.wav')
print(sample_rate)

A 44100

B data array

C wavfile.read object

D Error: file not found

💡 Hint

The first value returned by wavfile.read is the sample rate as an integer.

The wavfile.read function returns a tuple: (sample_rate, data). The sample rate is an integer representing samples per second.

❓ data_output

intermediate

Shape of data array from stereo WAV file

If you read a stereo WAV file with 1000 samples using scipy.io.wavfile.read, what is the shape of the data array?

SciPy

from scipy.io import wavfile
sample_rate, data = wavfile.read('stereo.wav')
print(data.shape)

A (2, 1000)

B (1000, 2)

C (1000,)

D (2000,)

💡 Hint

Stereo audio has two channels, so the data array has two columns.

For stereo WAV files, data is a 2D numpy array with shape (samples, channels). Here, 1000 samples and 2 channels means shape (1000, 2).

🔧 Debug

advanced

Error when writing WAV file with float data

What error will this code raise when trying to write a WAV file with float data using scipy.io.wavfile.write?

SciPy

from scipy.io import wavfile
import numpy as np
sample_rate = 44100
data = np.array([0.1, 0.2, 0.3], dtype=float)
wavfile.write('output.wav', sample_rate, data)

A TypeError: data type not supported

B SyntaxError

C No error, file written successfully

D ValueError: data must be integer type

💡 Hint

scipy.io.wavfile.write expects integer data types for PCM WAV files.

The write function requires integer arrays for PCM WAV files. Passing float arrays causes a ValueError.

🚀 Application

advanced

Normalize WAV audio data to range -1 to 1

Which code snippet correctly normalizes 16-bit PCM WAV data to float values between -1 and 1?

SciPy

from scipy.io import wavfile
sample_rate, data = wavfile.read('audio.wav')
# Normalize data here

A normalized = data / 65535.0

B normalized = data / 32768.0

C normalized = data.astype(float) / 32767.0

D normalized = data / 32767.0

💡 Hint

16-bit signed PCM ranges from -32768 to 32767; normalization uses max positive value.

To normalize 16-bit signed PCM data, convert to float and divide by 32767.0 to get range approximately -1 to 1.

🧠 Conceptual

expert

Effect of changing sample rate when writing WAV file

If you read a WAV file at 44100 Hz and write it back with a sample rate of 22050 Hz without changing data, what happens when playing the new file?

A Audio plays at half speed and one octave lower

B Audio plays normally with no change

C Audio plays at double speed and one octave higher

D Audio file is corrupted and won't play

💡 Hint

Lowering sample rate without changing data affects playback speed and pitch.

Writing the same data with half the sample rate causes playback at half speed and pitch drops one octave.