*Question E7F09:
Why is an anti-aliasing filter required in a decimator?*  

*Correct Answer is  A: It removes high-frequency signal components that would otherwise be reproduced as lower frequency components*  

### AI Response: (may contain errors)  

An anti-aliasing filter is crucial in a decimator to prevent aliasing, which occurs when high-frequency components of a signal are misinterpreted as lower frequency components during the sampling process. Here's a breakdown of the correct answer and why the other choices are incorrect:

### Correct Answer:  
**A: It removes high-frequency signal components that would otherwise be reproduced as lower frequency components**

- **Explanation**: When a signal is sampled, any frequency components above half the sampling rate (the Nyquist frequency) can be misrepresented as lower frequencies. This phenomenon is known as aliasing. An anti-aliasing filter is a low-pass filter that removes these high-frequency components before the signal is decimated (down-sampled), ensuring that only frequencies below the Nyquist frequency are present. This prevents aliasing and ensures accurate signal representation.

### Incorrect Choices:

- **B: It peaks the response of the decimator, improving bandwidth**
  - **Explanation**: An anti-aliasing filter does not peak the response or improve bandwidth. Instead, it limits the bandwidth by removing high-frequency components to prevent aliasing.

- **C: It removes low-frequency signal components to eliminate the need for DC restoration**
  - **Explanation**: The purpose of an anti-aliasing filter is not to remove low-frequency components. It specifically targets high-frequency components to prevent aliasing. DC restoration is unrelated to the function of an anti-aliasing filter.

- **D: It notches out the sampling frequency to avoid sampling errors**
  - **Explanation**: An anti-aliasing filter is not designed to notch out the sampling frequency. Its role is to remove frequencies above the Nyquist frequency, not to address the sampling frequency directly.

### Key Concept:

- **Nyquist Frequency**: The Nyquist frequency is half the sampling rate. To avoid aliasing, the signal must be band-limited to frequencies below this threshold before sampling. The anti-aliasing filter ensures this condition is met.