*Question E4E02:
Which of the following types of noise can often be reduced by a digital noise reduction?*  

*Correct Answer is  D: All these choices are correct*  

### AI Response: (may contain errors)  

To understand why the correct answer is "All these choices are correct," let's break down the types of noise mentioned and how digital noise reduction can affect them.

1. **Digital Noise Reduction**:  
   Digital noise reduction techniques analyze incoming signals and can filter out unwanted noise based on specific characteristics. This is particularly effective for noise that has a consistent pattern or frequency.

2. **Explanation of Choices**:
   - **A: Broadband white noise**:  
     This type of noise contains a wide range of frequencies and can be reduced using digital filtering techniques that target specific frequency ranges, allowing the desired signal to be preserved while attenuating the noise.
   
   - **B: Ignition noise**:  
     Ignition noise, often caused by electrical interference from vehicle ignition systems, typically has a recognizable pattern. Digital noise reduction can identify and filter out this noise, improving the clarity of the received signal.
   
   - **C: Power line noise**:  
     Power line noise usually manifests as a 60 Hz hum (or 50 Hz in some regions) and its harmonics. Digital noise reduction can effectively target these frequencies, allowing for the removal of this interference from the desired signal.

3. **Why the Correct Answer is Correct**:  
   Since digital noise reduction can effectively reduce all types of noise listed (broadband white noise, ignition noise, and power line noise), the correct answer is indeed "All these choices are correct."

4. **Why the Other Choices are Incorrect**:  
   Each of the other choices (A, B, and C) is not incorrect on its own; rather, they are all types of noise that can be reduced by digital noise reduction. Therefore, selecting any single option would not fully encompass the capabilities of digital noise reduction.

In summary, digital noise reduction is versatile and can address various types of noise, making "All these choices are correct" the best answer.