SPL PQ Mastering EQ

The PQ is a unique equaliser for several reasons. It has two times five fully parametric filter bands, each of which can be switched between constant Q and proportional Q! And there's sheer unlimited headroom and a very special kind of EQ sound, thanks to 120V technology.

Recall of all settings is easy thanks to the potentiometers with 41 steps. Each filter band can be boosted or cut up to 20 dB. If only minimal changes are required, the 1/4 Gain switch can be used to reduce the boost or cut range from +/-20 dB to +/-5 dB. SPL have designed the frequency distribution to overlap widely between the bands, so that problematic frequencies can also be addressed with two bands.

The bandwidth Q determines the steepness of bell characteristic. A small Q is a wide bandwidth and a high Q a narrow bandwidth. The labelling of the scale is divided into two parts. The values with white background refer to the proportional Q mode and the values without background refer to the constant Q mode.

The blue button is used to toggle the Q mode. In constant Q mode, the amplitude is constant regardless of the selected bandwidth. This is ideal for eliminating interfering frequencies. In proportional Q mode, the amplitude is proportional to the bandwidth. It decreases with increasing bandwidth and vice versa. At the smallest bandwidth setting, the maximum amplitude value is +/- 20 dB, while the maximum amplitude decreases to +/- 2.8 dB at the largest bandwidth setting. This control behaviour simplifies sensitive, creative processing and is musically very useful, since high amplitudes become increasingly unusable with increasing bandwidth.