hD is a distortion effect. It can also directly add note harmonics — up to two octaves higher — and it contains a sub-octave Generator.
The Harmonic generators are optimized and located to enhance the distortion. They can also be used to generate 12-string guitar effects and as a note doubler. We developed a sub-octave generation algorithm specifically for this application. It is latency-free and is true to the sound of the input Signal. It is located in the signal path post distortion. It adds depth without overwhelming the distortion.
We use a parametric EQ, xEQ, with hD. You can download xEQ for free. We have some suggestions in hD's User Guide about how best to use EQ and also some tips for setting the harmonics. The sound samples are generated with one xEQ before hD and one after.