*Question E7F02:
What kind of digital signal processing audio filter is used to remove unwanted noise from a received SSB signal?*  

*Correct Answer is  A: An adaptive filter*  

### AI Response: (may contain errors)  

To understand the correct answer to the question about digital signal processing audio filters used to remove unwanted noise from a received SSB (Single Sideband) signal, let's break down the options:

### Correct Answer: A: An adaptive filter

- **Why it's correct**:  
  An adaptive filter is designed to adjust its parameters automatically based on the characteristics of the input signal. This makes it particularly effective for noise cancellation in SSB signals, where the noise characteristics can vary over time. The filter can adapt to the changing noise environment, allowing it to effectively remove unwanted noise while preserving the desired signal.

### Why the other choices are incorrect:

- **B: A crystal-lattice filter**:  
  Crystal-lattice filters are typically used for frequency selection and are not adaptive. They are fixed filters that provide a specific frequency response and are not designed to remove noise dynamically.

- **C: A Hilbert-transform filter**:  
  Hilbert-transform filters are used primarily for phase shifting and creating analytic signals. While they can be useful in signal processing, they do not specifically target noise removal in the way adaptive filters do.

- **D: A phase-inverting filter**:  
  Phase-inverting filters can invert the phase of a signal but do not inherently remove noise. They are not adaptive and do not adjust to the noise characteristics of the incoming signal.

### Summary

- **Adaptive filters** are the best choice for noise removal in SSB signals due to their ability to adjust to changing noise conditions.
- The other options are either fixed filters or serve different purposes in signal processing.

### Useful Rule of Thumb

When dealing with noise in communication systems, always consider using adaptive filtering techniques for dynamic environments, as they provide the flexibility needed to effectively isolate and enhance the desired signal.