Question

What is the difference between shelf and peak/notch filters in EQ?

Answer 1

In the context of equalizers (EQ), **shelf** and **peak/notch** filters serve different purposes for shaping audio frequencies:

### 1. **Shelf Filter**:
- **Function**: A shelf filter boosts or cuts frequencies either above (high-shelf) or below (low-shelf) a certain cutoff frequency. It affects all frequencies beyond the set point, either amplifying or attenuating them smoothly.
- **Types**:
  - **Low-shelf filter**: Affects frequencies below the cutoff frequency.
  - **High-shelf filter**: Affects frequencies above the cutoff frequency.
- **Shape**: The response curve looks like a "shelf," hence the name. When boosting, it rises and flattens; when cutting, it drops and flattens.
- **Use**: Commonly used for adjusting the overall brightness (high-shelf) or bass (low-shelf) of a sound.

### 2. **Peak/Notch Filter**:
- **Function**: A peak/notch filter boosts (peak) or cuts (notch) frequencies around a specific center frequency, leaving the rest of the frequency spectrum relatively unaffected.
- **Shape**: The response curve forms a peak (for boosting) or a dip/notch (for cutting), centered around the target frequency. The sharpness or width of the peak/notch is determined by the **Q factor** (bandwidth).
  - **Higher Q**: Narrower bandwidth, affecting a smaller range of frequencies.
  - **Lower Q**: Wider bandwidth, affecting a broader range of frequencies.
- **Use**: Peak filters are used for emphasizing particular frequency ranges, while notch filters are for removing unwanted frequencies (e.g., hums or resonances).

### Key Differences:
- **Shelf filter** affects a broad range of frequencies either below or above the cutoff point.
- **Peak/Notch filter** targets a specific frequency band for more precise adjustments.

These filters are essential tools in audio production for fine-tuning the tonal balance and addressing specific audio issues.

Answer 2

The difference between **shelf filters** and **peak/notch filters** in an equalizer (EQ) lies in how they shape the frequency response of an audio signal:

### 1. **Shelf Filters**
- **Shelf filters** affect all frequencies beyond a certain cutoff point.
- They come in two types:
  - **Low-shelf filter**: Boosts or cuts frequencies **below** a certain point.
  - **High-shelf filter**: Boosts or cuts frequencies **above** a certain point.
- After the cutoff frequency, the gain remains the same for all frequencies.
  
**Example**: A low-shelf filter might boost all frequencies below 100 Hz by 5 dB, giving more bass presence to the sound.

### 2. **Peak/Notch Filters**
- **Peak filters** (also called **bell filters**) boost or cut frequencies around a certain center frequency, forming a bell shape on the EQ curve.
- **Notch filters** are similar but more focused on cutting a very narrow range of frequencies, creating a dip (or notch) in the frequency response.
- The filter affects a narrow band of frequencies around the selected frequency, with the steepness controlled by the **Q factor** (bandwidth).

**Example**: A peak filter could boost frequencies around 1 kHz, while a notch filter could remove a specific, narrow range of frequencies at 500 Hz to eliminate noise or feedback.

### Summary:
- **Shelf filters** affect a broad range (above or below the cutoff).
- **Peak/notch filters** focus on a specific frequency band and can either boost (peak) or cut (notch) around the selected frequency.