Plant-based Techno

While many of Cogapp’s hack days have external collaborators or themes, April’s Cogapp hack day was free-form. I had recently read an article in Create Digital Music about people connecting synthesizers to plants, so when it came to choosing an idea, I knew immediately that I wanted to give Biodata Sonification a go: I have plenty of plants around the house that are lovely to look at but what do they sound like?

There are a few products that claim to turn signals from plants into music: the most polished is probably the Plantwave, a tiny box that picks up signals from the plant’s leaves via a pair of electrodes and wirelessly connects to mobile apps to generate music (it has a MIDI output as well for connecting to other sound sources); if you’re into modular synthesis, you can also buy a DIY synthesiser module which serves a similar function. Unfortunately, these are priced at $299 and £196 respectively which puts them a little out of my price range.

After a bit of googling, I found a number of DIY versions using an Arduino microcontroller board and standard electronic components. I eventually settled on the BiodataSonificationBreadboardKit project by Sam Cusumano. The whole building process is explained in a PDF with photos of every step. I already had an Arduino and solderless breadboard to hand, and all the other components could be sourced easily from eBay.

The function of the circuit and Arduino code is to detect small variations in conductivity across two electrodes and convert these to MIDI notes. For better adherence to surfaces like leaves, the electrodes are fitted with reusable sticky pads like those used on Transcutaneous Electrical Nerve Stimulation (TENS) machines.

I haven’t yet been able to determine whether the generated signal is directly related to electrical impulses generated by the plant or simply variations in electrical interference. The inventor of the device has made longer recordings and noted a difference in pitches between morning and evening implying that some biological process is at work.

As someone whose day job has been working with software for the last seven and a bit years, I had forgotten some of the complexities that crop up when working with hardware. There were a few problems, some of which were not my fault (a faulty 555 timer) and others which definitely were (I was getting zero signal for longer than I would care to admit before discovering I’d plugged two wires into the wrong outputs on the Arduino). There was also an issue with the connection of the 3.5mm jack: it kept falling off the breadboard due to the weight of the electrode cables but after a quick and dirty soldering job I managed to get it behaving a little more consistently.

After I had finished assembling the circuit and connecting everything up (the correct way this time) I stuck the sticky pads onto a Snake plant or Sansevieria. Then came the choice of which instrument to send these MIDI signals to. The Biodata Sonification device outputs polyphonic (many notes / voices) MIDI data, but for my first experiment, I tried connecting it to a monophonic (one note at a time) synthesizer, a Korg NTS-1.

By default, the device outputs notes in a chromatic scale: that’s all the keys on a piano, both white and black. There is also no quantization (adjustment to fall on specific beats / fractions of beats) of note start or end times to a regular rhythm. These factors both contribute to a very loose, random-sounding arrangement of notes which isn’t particularly musical.

During my initial test, I made the happy discovery that touching the leaves with my hands while they were connected to the device had an effect on the pitches generated, providing an opportunity for human-plant collaboration which I hadn’t foreseen.

The random nature of the sound lends itself more to less structured, more ambient music. Here’s an example of the device hooked up to a polyphonic software synthesiser, still un-quantized but mapped to a Major scale:

Much more pleasing, but I wanted to make something a bit more structured. While the plant itself doesn’t know about musical dissonance or consonance, by processing the incoming MIDI signal to restrict pitches and timing, I could attempt to generate something that sounds more like ‘real’ music. Adding some drums and sending the MIDI signal to a bass synthesizer with real-time controls allowed me to collaborate with the plant to make some satisfying, if somewhat aimless, dance music.

From my short time using it, I’ve found that the Biodata Sonification device is a great way to introduce some random input to my music making. My experiments so far have involved mapping the output of the device to musical pitches but it also supports Control Voltage (CV), meaning that it can be used to control any number of parameters on a hardware synthesizer from filter cutoff frequency to delay time.

If you’re into novel ways to make music and like to tinker with electronics, this is a fantastic project to try. I’m looking forward to assembling more of the devices so I can build a whole botanical orchestra from the plants in the Cogapp office.

I’d love to hear any thoughts you may have on this project in the comments.