*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 remove unwanted noise from a received Single Sideband (SSB) signal, an adaptive filter is used. Here's why:

1. **Correct Answer: An adaptive filter**
   - **Explanation**: Adaptive filters are designed to adjust their parameters automatically to minimize the noise in a signal. They are particularly effective in environments where the noise characteristics change over time. This makes them suitable for processing SSB signals, which can be affected by varying noise conditions.

2. **Why the other choices are incorrect:**
   - **B: A crystal-lattice filter**
     - Crystal-lattice filters are fixed-frequency filters that are not capable of adapting to changing noise conditions. They are typically used for precise frequency selection rather than noise reduction.
   - **C: A Hilbert-transform filter**
     - Hilbert-transform filters are used to create a phase shift of 90 degrees, which is useful in generating single sideband signals but not specifically for noise reduction.
   - **D: A phase-inverting filter**
     - Phase-inverting filters are used to invert the phase of a signal, which is not directly related to noise reduction in SSB signals.

In summary, adaptive filters are the best choice for dynamically reducing noise in SSB signals due to their ability to adjust to changing noise environments.