Hydrogen can be used as MIDI synth for your MIDI device. All settings in both Instrument Editor and Mixer are applied but instead of notes picked up from patterns while playback is rolling, incoming MIDI messages will trigger sounds. In addition, all incoming MIDI notes can be recorded.
NOTE_ON type MIDI messages will trigger a note while NOTE_OFF will stop all note rendering in the corresponding instrument. This behavior might be exactly what you expected from an edrum but, on the other hand, also might be a pain when using a MIDI keyboard (since releasing a key will stop the note). In this case you can disable NOTE_OFF message handling by unchecking Ignore note-off in the Preferences.
Which incoming MIDI note is mapped to which particular
instrument does depend on multiple settings. First of all, each
NOTE_ON message is assigned a channel - the default one in the General
MIDI standard is
10. Using Channel in the
Preferences you can set whether Hydrogen should listen to incoming
notes on all channels or just to a single one. The second degree of
freedom of a note is its pitch. Depending on the current Input Mode it is either
mapped to a pitch-shifted sample of the currently selected instrument
or an instrument of the current drumkit. The latter will be discussed
in section MIDI Note
Mapping in more detail.
When NOTE_ON messages are mapped to Actions they will be discarded and do not trigger sound when Discard MIDI messages after action has been triggered is checked in the Preferences.
Using Input Mode in Options within the Main Menu you can choose between two different ways of triggering sounds and record notes.
Drumkit maps different MIDI notes
Keyboard strokes) to different instruments of the current
Instrument, on the other hand, maps them to
pitch-shifted samples of the instrument currently selected in the
Pattern Editor. You can
use these modes to record notes into both Drumkit Editor and Piano Roll Editor
respectively. The third property of a MIDI note, its
velocity, will be used as velocity for the triggered note.
If Input Mode was
Drumkit, Hydrogen has two ways of dealing
with incoming MIDI notes: order-based and output-based.
Per default mapping in done order-based. Hydrogen maps incoming
MIDI notes of pitch
36 and above to
instruments of your drumkit. A MIDI note of pitch
36 will trigger a sample of the first instrument of
your current drumkit, one of pitch
37 a sample from
the second one and so forth. When choosing this option you can
control mapping by drag-dropping the instruments into the desired
Alternatively you can use output-based mapping by checking Use output note as input note in the Preferences. This way an incoming MIDI note is mapped to the instrument which's MIDI Output Note setting in the Instrument Editor matches its pitch.