It seems that Hydrogen software supports both import and export of standard WAV audio and thus you can use to export, .h2song drum notations to audio format using the default export function.
Convert Hydrogen drum notes to WAVe PCM Sound, standard Windows sound format.
We found one software available in the database for this conversion.
Linux/Unix software - convert h2song to wav on Linux
A software synthesizer for Unix and Unix-based operating systems.
Convert from h2song file format
The table with program actions contains information about what each program is capable of doing with their files. This may be a good pointer for further searches for certain file conversions and help you find the converter you are looking for if our search result is insufficient for you. However, it is far from perfect and may sometimes show results which are not really usable because of the nature of the software handles the files. So a conversion that appears as possible, just because of matched actions, may in fact not be possible.