HEX-98 is a harmonic exciter that adds warmth, presence, and harmonic content to audio. It uses frequency-selective processing (typically high-pass filtering to isolate the range you want to excite) and saturation to generate even and odd harmonics. You get multiple saturation modes (e.g. Tube, Tape, Digital), drive, mix, tone/character, and output level.
 
Drive sets how much saturation is applied and therefore how strong the harmonic enhancement is. Low drive adds subtle warmth; high drive adds obvious brightness and edge. Mix blends the processed (wet) signal with the original (dry) so you can parallel process or go full wet. Tone or Character shapes the frequency balance of the effect (e.g. more or less high-frequency emphasis). Output is the final level trim. Frequency (or similar) targets which part of the spectrum is processed (e.g. high-pass around 1 kHz so only the upper range gets excited). Mode selects the saturation type: Tube for smooth, warm harmonics; Tape for a slightly softer, vintage character; Digital for a cleaner, more modern edge. The exact names and number of modes may vary; the idea is to choose a harmonic flavour that fits the source.
 
The interface typically includes a spectrum display so you can see the input and the effect of the exciter.
 
Ideal for mix engineers and producers who want to add analog-style warmth and clarity without a full chain of saturation and EQ.