The Guyatone PS-008 is a vintage pedal from the Japanese-made Efect Box series. It is a single-band parametric equaliser with control over frequency, width and gain / attenuation.

Gain
Turning this control clockwise (in the + direction) emphasises (+ 18dB = 8 times) the band set by the Frequency control, and turning it counterclockwise (in the – direction) attenuates (-18dB = 1/8) the same.
At the centre (0 position) of the knob, meanwhile, the frequency characteristics become flat irrespective of the other two knobs’ position

Width
This knob controls the width of the frequency band set by the Frequency control. Turning it clockwise decreases (1 octave) the width, and turning it counterclockwise increases (2 octaves) the width.

Frequency
This knob controls the frequency to be emphasised or attenuated. Turning it clockwise shifts the centre frequency toward high tones (5,000Hz), and turning it counterclockwise shifts the same toward low tones (70Hz).