Audio compression basics in Signal Processing - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to calculate the duration of an audio clip in seconds.

Signal Processing

duration = num_samples [1] sample_rate

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

A/

B*

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of division

Adding sample_rate instead of dividing

Duration is the number of samples divided by the sample rate.

2fill in blank

medium

Complete the code to compute the bit rate of an audio file.

Signal Processing

bit_rate = sample_rate [1] bit_depth [2] channels

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

A*

B/

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using division or addition instead of multiplication

Bit rate is sample rate times bit depth times number of channels.

3fill in blank

hard

Fix the error in the code to normalize audio samples between -1 and 1.

Signal Processing

normalized_samples = samples [1] max(abs(samples))

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

A/

B*

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of division

Adding or subtracting max value

To normalize, divide samples by the maximum absolute value.

4fill in blank

hard

Fill both blanks to create a dictionary of word lengths for words longer than 3 characters.

Signal Processing

{word: [1] for word in words if len(word) [2] 3}

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

Alen(word)

Bword

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using word instead of len(word)

Using '<=' instead of '>'

The dictionary maps each word to its length if the word length is greater than 3.

5fill in blank

hard

Fill all three blanks to create a dictionary of uppercase words and their lengths for words longer than 4.

Signal Processing

{ [1]: [2] for [3] in words if len([3]) > 4 }

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

Aw.upper()

Blen(w)

Cword

Dw

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'word' instead of 'w' in the comprehension

Not converting to uppercase

The dictionary uses uppercase words as keys and their lengths as values, iterating with variable 'w'.

Practice

1. What is the main goal of audio compression?

easy

A. To reduce the file size while keeping sound quality acceptable

B. To increase the file size for better quality

C. To convert audio files into video files

D. To remove all background noise completely

Solution

1. Step 1: Understand the purpose of audio compression

   Audio compression aims to make audio files smaller so they use less space and bandwidth.

2. Step 2: Identify the correct goal

   The goal is to reduce size but keep the sound quality good enough for listening.

3. Final Answer:

   To reduce the file size while keeping sound quality acceptable -> Option A

4. Quick Check:

   Audio compression = smaller files with good quality [OK]

Hint: Compression means smaller size, not bigger [OK]

Common Mistakes:

• Thinking compression increases file size
• Confusing audio with video conversion
• Assuming all noise is removed

2. Which of the following is a correct statement about lossy audio compression?

easy

A. It keeps all original audio data intact

B. It removes some audio data permanently to reduce size

C. It converts audio to text format

D. It increases the audio file size

Solution

1. Step 1: Define lossy compression

   Lossy compression removes some audio data permanently to save space.

2. Step 2: Compare options

   Only It removes some audio data permanently to reduce size correctly describes lossy compression; others are incorrect or unrelated.

3. Final Answer:

   It removes some audio data permanently to reduce size -> Option B

4. Quick Check:

   Lossy = data removed permanently [OK]

Hint: Lossy means some data is lost forever [OK]

Common Mistakes:

• Confusing lossy with lossless compression
• Thinking lossy keeps all data
• Believing audio is converted to text

3. Consider this Python code snippet simulating audio compression bitrate calculation:

original_bitrate = 1411  # in kbps for CD quality
compression_ratio = 0.1
compressed_bitrate = original_bitrate * compression_ratio
print(int(compressed_bitrate))

What is the output of this code?

medium

A. 1411

B. 14

C. 141

D. 0

Solution

1. Step 1: Calculate compressed bitrate

   Multiply original bitrate 1411 kbps by compression ratio 0.1: 1411 * 0.1 = 141.1

2. Step 2: Convert to integer and print

   int(141.1) is 141, so the output is 141.

3. Final Answer:

   141 -> Option C

4. Quick Check:

   1411 * 0.1 = 141 [OK]

Hint: Multiply bitrate by ratio, then convert to int [OK]

Common Mistakes:

• Forgetting to multiply by compression ratio
• Confusing int conversion rounding
• Printing original bitrate instead

4. This code tries to calculate compressed audio size but has an error:

file_size_mb = 50
compression_rate = 0.2
compressed_size = file_size_mb / compression_rate
print(compressed_size)

What is the error in this code?

medium

A. Division by zero error

B. Variable names are invalid

C. Missing import statement

D. It should multiply, not divide, by compression_rate

Solution

1. Step 1: Understand compression calculation

   Compressed size should be original size multiplied by compression rate (fraction less than 1).

2. Step 2: Identify the error in code

   The code divides file_size_mb by compression_rate, which increases size incorrectly.

3. Final Answer:

   It should multiply, not divide, by compression_rate -> Option D

4. Quick Check:

   Compression size = original size * rate [OK]

Hint: Compression reduces size, so multiply by rate [OK]

Common Mistakes:

• Using division instead of multiplication
• Assuming variable names cause error
• Expecting import needed for math

5. You have a 100 MB audio file and want to compress it to about 25% of its size using lossy compression. Which bitrate should you choose if the original bitrate is 160 kbps?

Options:
A) 40 kbps
B) 80 kbps
C) 120 kbps
D) 160 kbps

hard

A. 40 kbps

B. 80 kbps

C. 120 kbps

D. 160 kbps

Solution

1. Step 1: Calculate target bitrate for 25% size

   25% means 0.25 times original bitrate: 160 kbps * 0.25 = 40 kbps.

2. Step 2: Choose bitrate matching target

   40 kbps is 40 kbps, which matches the target bitrate for 25% size.

3. Final Answer:

   40 kbps -> Option A

4. Quick Check:

   160 * 0.25 = 40 kbps [OK]

Hint: Multiply original bitrate by compression fraction [OK]

Common Mistakes:

• Choosing bitrate higher than target size
• Confusing percentage with absolute value
• Ignoring lossy compression effect