The equaliser included with the Duende EQ and Dynamics Channel Strip plug-in is a four band parametric EQ. Based on the XL 9000K EQ circuit, this plug-in includes two distinct EQ curves, one based on the SSL G series EQ and another based on the latest version of SSL’s classic E series EQ.
Normally these shelving curves have a degree of overshoot/undershoot (depending on whether you are boosting or cutting) below the selected HF frequency or above the selected LF frequency. Selecting the E button removes the overshoot/undershoot effect and provides a slightly gentler slope.
Normally, at any Q setting, the bandwidth of the HMF and LMF sections varies with gain, whereby an increase in boost or cut increases the selectivity of the EQ. This type of EQ can sound effective when used at moderate settings; the gentle Q curve lends itself to the application of overall EQ on combined sources and subtle corrective adjustments to instruments and vocals.

When the EQ is switched to ‘E’ operation, the bandwidth of the HMF and LMF sections remains constant at all gains, so at lower gains the EQ curves are comparatively narrower for a given Q setting. This is particularly useful for drums, since relatively high Q is available at low gain settings. However, it is not so suitable for overall EQ or subtle corrections, as you need to adjust the Q to maintain the same effect when the gain is changed.
• Normal (G type) curves with the ‘E’ switch OUT, have a modified slope with a degree of overshoot/undershoot for increased selectivity
• ‘E type’ curves with the ‘E’ switch IN follow conventional cut or boost characteristics
• The two parametric bands have selectable characteristics which affect the relationship between frequency bandwidth and gain (see the lower plot, opposite):
• With the ‘E’ switch OUT, the frequency bandwidth reduces with increased gain, thereby increasing the selectivity of the EQ as the gain is increased.
• With the ‘E’ switch IN, the frequency bandwidth is constant at all gains
• At full boost or cut both are identical