In addition to manually program patterns using mouse and keyboard you can also record one or multiple patterns. You can do so using an external MIDI device, like an e-drum, or use the Virtual Keyboard provided by Hydrogen.
In order to start recording, first activate the record button in the Main Toolbar and afterwards press the button located right next to it (like in a classical tape recorder).
Using the playback mode of the Song Editor you can choose between the following two scenarios. When in Pattern Mode all inserted notes will be added to the pattern currently selected in the Sidebar of the Song Editor. When, on the other hand, in Song Mode the input notes will be added to the active pattern (the one the playhead is located in and is currently used for playback). If several patterns are selected in a single row, the input notes will only be added to the pattern at the bottom.
By locking the Pattern Editor in Song Mode Hydrogen will automatically select the pattern recorded notes will be inserted to.
The incoming notes will be added in a non-destructive way. This means when attempting to add a notes at a position already containing one of equal pitch, the new note will be discarded and the old one kept.
You can also limit patterns new notes will be recorded to by defining a continuous punch in area via right click and dragging the cursor to the right in the ruler of the Song Editor.