This is a Boss EH-2 Enhancer, a guitar effects pedal produced from 1990 to 1998. Unlike a standard static equalizer, it acts as a dynamic, frequency-dependent harmonic expander—essentially a "reverse compressor" that dynamically boosts or cuts high-end clarity based on your picking strength.  Control Panel Overview

• MIX: Blends the processed signal with your dry tone. 12:00 is neutral (no effect). Turning right (NOR) mixes the enhancement in a normal phase to boost sparkle. Turning left (INV) mixes it in an inverted phase to subtract or reshape frequencies. 
• FREQ: Sets the specific frequency center range (from roughly 3 kHz to 10 kHz) that the pedal targets for enhancement. [1
• SENS: Controls the threshold or sensitivity. Setting it higher triggers the effect on softer notes, while lower settings require hard picking dynamics to engage the upper shimmer. 

💡 Core Applications

• Restore Highs: Placed at the end of a signal chain or in an amp effects loop to bring back high-end clarity lost from long cables or buffered setups. 
• Tone Sweetener: Acts as a subtle "always-on" studio-like polish to give lead parts extra sheen or brighten darker pickups without adding harsh fixed treble. Open box. Like new