# How to create a Hydrogen drumkit for fun and profit

Drum machines are fun. They can make some amazing beats, and also because, at least traditionally, they tend to have an easy interface.

The first drum machine I ever used was the [Alesis HR-16](http://www.vintagesynth.com/misc/hr16.php). 
It had 49 16-bit patches and an inbuilt sequencer.
It annoyed me that it wasn't rack mountable, but then again, it fit into a messenger bag, so I was able to easily take it to studio sessions.

The HR-16's interface was one of the best. 
Its only display was a two line LCD screen, and all of its functions had dedicated buttons on the front of the machine. 
To build up a new drum line, you selected a pattern slot, entered recording mode, and played in a beat either in real time or beat-by-beat.
The unit held up to 100 patterns, and you could string together several patterns into up to a 100 song files.

Today, I use the [Hydrogen](http://hydrogen-music.org/hcms/) software drum machine.
The concept is basically the same: enter a rhythm into the active pattern, and then build a song of patterns. 
It's simple, intuitive, and it makes you feel like a rock 'n roller in no time.

The great thing about Hydrogen is that it isn't limited to a single chip of 49 16-bit sounds. 
You can build your own drumkits with your own sounds.
This means that anything you want to make a rhythm out of, you can record, and then sequence within Hydrogen. Amazingly, it's not even that hard.


## Anatomy of a kit

A Hydrogen drumkit is actually just ``.tar`` using a ``.h2drumkit`` as an extension.

    $ file ./mydrumkit.h2drumkit
    mydrumkit.h2drumkit: POSIX tar archive (GNU)

Contained within the TAR archive are the sounds that you want to use as your drumkit and an XML file describing the drumkit to Hydrogen. This looks a little something like this:

    <instrument>
        &#60;id>0</id&#62;
	&#60;name>Kick drum</name&#62;
        &#60;volume>1</volume&#62;
        &#60;isMuted>false</isMuted&#62;
        &#60;pan_L>1</pan_L&#62;
        &#60;pan_R>1</pan_R&#62;
        &#60;randomPitchFactor>0</randomPitchFactor&#62;
        &#60;filterActive>false</filterActive&#62;
        &#60;filterCutoff>1</filterCutoff&#62;
        &#60;filterResonance>0</filterResonance&#62;
        &#60;Attack>0</Attack&#62;
        &#60;Decay>0</Decay&#62;
        &#60;Sustain>1</Sustain&#62;
        &#60;Release>1000</Release&#62;
        &#60;exclude /&#62;
	&#60;layer&#62;
	    &#60;filename>35kick.flac</filename&#62;
            &#60;min>0</min&#62;
            &#60;max>1</max&#62;
            &#60;gain>1</gain&#62;
            &#60;pitch>0</pitch&#62;
            &#60;/layer&#62;
    &#60;/instrument&#62;


Building a drumkit, therefore, is as simple as:

1. Gather the sound files you want in your kit
2. Generate an XML file describing your kit
3. Create a ``tar`` file and load it into Hydrogen


## 1. Sounds 

Your sound files can come from anywhere. You can record your own vocal
beatboxing, you can record the drumset in your bedroom, you can record
sounds of nature, you can pillage
[freesound.org](http://freesound.org), and whatever else you can
imagine.

If your sound files are not in the FLAC format, convert them to FLAC
with an audio converter like [sox](http://sox.sourceforge.net/),
[ffmpeg](http://ffmpeg.org), or
[Audacity](http://www.audacityteam.org/).

With sox:

    $ sox foo.wav foo.flac

With ffmpeg, add the ``-vn`` flag to ensure no video is included in
the conversion process:

    $ ffmpeg -i foo.wav -vn foo.flac

And in Audacity, load the source sound file and use the **File** &#62;
**Export audio** menu selection. In the **Export audio** window,
select FLAC as your output format.

### Arranging the sound files

Technically, your drum kit can have sound files in any order you want
or in whatever order they end up being sorted by your terminal
listing. However, a long time ago some very smart music technicians
came up with a specification for how sounds should be organised in the
world of synthesis. They call the spec [General
MIDI](https://www.midi.org/specifications/item/gm-level-1-sound-set),
or just **GM** for short.

The advantage of General MIDI is that a musician can compose a song or
drum sequence with one sound bank, and then swap sound banks (or
"drumkits" in Hydrogen's terminology) and still have essentially the
same thing, just with different sounds. Your bass drum is still a base
drum, your snare is still a snare, and your cymbal is still a cymbal,
but the sample behind those sounds has been swapped. You can write one
drum sequence and use it in both the electro-metal intro version as
well as the delicate acoustic ballad version of the same song.

You don't *have* to follow GM, but it's not a bad idea.

To keep my drum kit sounds organised, I name the sounds in each kit
according to GM specification.

    $ ls mydrumkit/
    35kick.flac
    36kick.flac
    37click.flac
    38snare.flac
    40snare.flac
    41tom_low.flac
    ...

If I don't have a sound that the GM has a slot for, I just skip that
slot.

This method also avoids wildly variable naming schemes. There's no
**kick drum BIG.flac** and **bass drum deep.flac** files in my
kits.

When a kit that I make manages to populate the GM spec completely, I
give it the **full** designation, just so users know that the drum kit
is truly GM compatible.

## 2. Create a drumkit.xml file

People sometimes get irrationally scared of XML, presumably because it
seemingly has unlimited tags with no clear definition of what tags are
required or even what they mean.

The ``drumkit.xml`` file in a Hydrogen drumkit is mostly repetitive,
and simple enough to generate by hand. All you really need is a text
editor and the willingness to copy and paste. A lot.

The header portion of your drumkit definition opens a ``drumkit_info``
element, and provides metadata about the kit:

    &#60;drumkit_info&#62;
        &#60;name>
	  mydrumkit
	&#60;/name>
        &#60;author>
          Seth
	&#60;/author>
        &#60;info>
          This is my first drumkit. It contains sounds released under
          the CC-0 license.
        &#60;/info&#62;
	&#60;license>
	  CC-0
	&#60;/license>
	&#60;instrumentList>

This is entered once, and only once, per kit, at the top of your file.

For each sound file, assuming one sound file represents one
instrument, an ``instrument`` block is required. The basic instrument
block starts with this:

    &#60;instrument&#62;
        &#60;id>0</id&#62;
	&#60;name>Kick drum</name&#62;
        &#60;volume>1</volume&#62;
        &#60;isMuted>false</isMuted&#62;
        &#60;pan_L>1</pan_L&#62;
        &#60;pan_R>1</pan_R&#62;
        &#60;randomPitchFactor>0</randomPitchFactor&#62;
        &#60;filterActive>false</filterActive&#62;
        &#60;filterCutoff>1</filterCutoff&#62;
        &#60;filterResonance>0</filterResonance&#62;
        &#60;Attack>0</Attack&#62;
        &#60;Decay>0</Decay&#62;
        &#60;Sustain>1</Sustain&#62;
        &#60;Release>1000</Release&#62;
        &#60;exclude /&#62;

Once you get the hang of creating drumkits, there are some neat tricks
for using multiple sound files for one instrument that you can
explore. After all, a cymbal, for instance, being tapped has a unique
sound quality compared to a cymbal being pounded with a drumstick, but
it's still the same physical instrument.

For now, though, keep your instruments simple and just use one file
per instrument. Sound files are referenced in the instrument's
``layer`` block:

    &#60;layer&#62;
      &#60;filename>35kick.flac</filename&#62;
      &#60;min>0</min&#62;
      &#60;max>1</max&#62;
      &#60;gain>1</gain&#62;
      &#60;pitch>0</pitch&#62;
    &#60;/layer&#62;
    &#60;/instrument&#62;

Repeat that process for each sound file, and then close your
``instrumentList`` and ``drumkit_info`` tags:

    &#60;/instrumentList>
    &#60;/drumkit_info>

That's all the XML you need to know!


## 3. Create a tar archive

The final step in this process is to wrap your sounds and XML in an
archive.

If you haven't already, place your sound files and your
``drumkit.xml`` file into a dedicated directory. Assume the directory
is called ``mydrumkit`` (although in real life, I do hope you come up
with something more creative).

Run the ``tar`` command:

    $ tar cvf mydrumkit.tar mydrumkit

And then rename your TAR archive so Hydrogen recognises it:

    $ mv mydrumkit.tar mydrumkit.h2drumkit

You're done! That's all there is to it. You've just made your very own
custom kit.


## Loading your kit

To use your drumkit in Hydrogen, you must import it.

To import a drumkit, open Hydrogen and click on the **Instruments**
menu and select **Import Library**.

![](menu-hyrdrogen-import.jpg)

In the **Sound Library Import** window, click the **Local file**
tab. Click the **Browse** button on the right.

Select your drumkit file to load it. The import process takes only a
second, so don't be surprised if it seems to happen too quickly.

To use your kit, right-click on your drumkit in the **Sound Library**
tab of the Hydrogen window and select **Load**.

![](load.jpg)

If you already had data entered into a Hydrogen pattern, your data
will still be there after switching kits. If you followed GM, your
sequence should sound basically the same, just played on a different
drum kit!


## Automation

A few years ago, me and a friend created 99 Hydrogen drum kits over
the course of a few weeks. Organising over a thousand sound files was
something we had to do by hand (and ear), but the last thing we wanted
to do after all that work was generate 99 ``drumkit.xml`` files
manually. Instead, I wrote a simple Python script to do the repetitive
stuff for us.

The script is called ``genhydro``, and its sole purpose is to generate
a ``drumkit.xml`` file from a directory full of FLAC files, and create
an archive of the directory.

You can find the script over at
https://gitlab.com/genhydro/genhydro. Feel free to use it if you don't
want to generate the XML by hand.


## Benefitting from the hard work of others

Hydrogen has a strong and creative community. You can download
drumkits from other users from the **Import Library** window.

Additionally, you can download my 99 drumkits from
http://slackermedia.info/sprints/multimediaSprint_v2/99_hydrogenDrumkits.tar

Now go make some great beats!