When I first heard Senyawa's music about a year or so ago it stopped me dead in my tracks. My friend Jimmy Martin (occasional writer for this site and member of Teeth Of The Sea) posted some YouTubes of the duo performing on his Facebook and I was one of many people posting some kind of variation on "WTF?" underneath it.

I was presented with an Indonesian duo, one of whom appeared to be playing some kind of harp made out of a length of drainpipe, and an effervescent singer who seemed to switch quite naturally between guttural roars, throat singing, harsh black metal vocalisations and even the mimicking of birdsong.

Deeper investigation revealed that the man on 'drainpipe' was called Wukir Suryadi and he was in fact playing a 100% unique and self-built bambuwukir, or 'bamboo instrument', which could produce similar sonic elements to the bass, harp, guitar and various percussion instruments, but could also create a dizzyingly wide sonic palette on top of this when used in conjunction with pedals and a bow.

The astoundingly inventive vocalist was called Rully Shabara Herman (frontman of Indonesian math rock group Zoo) and it seemed clear that he was performing a kind of audio balancing act: that no matter how diverse Suryadi's instrument was, he was determined to be able to create as many - if not more - sounds using his voice alone.

The pair were introduced to one another live on stage at the Yes No Klub in Yogyakarta, Indonesia in July 2011, so the group was formed before they had even exchanged greetings. But since then their output and work has been nothing short of incredible. They have performed with Andrew Mclennan, Yasukai Akai, Tatsuya Yoshida, Bae Il-Dong, Lucas Abela, KK Null, Keiji Haino, Melt-Banana, Jon Sass, Damo Suzuki, Jerome Cooper, David Shea, Kazu Ushihashi and Joel Stern, not to mention touring with Regurgitator. They haven't found much of an audience to speak of at home but have been causing waves every time they play in places such as Australia and Europe (this is really no surprise; listen to the live album embedded below). They have released a wealth of music, including several live albums, a collaboration with Arrington De Dionyso and two studio albums, the second of which, Menjadi, came out earlier this year on Rabih Beaini's Morphine label.

I interviewed Herman about a year ago but then didn't get round to publishing the feature due to ill health. Since then I've heard a rumour that Sub Pop are considering them for a release… let's hope so. Whether or not that comes to pass, they are playing Cafe OTO in London next week (full details below), so head to see them then.

Can you explain what the name Senyawa means?

Rully Shabara Herman: A literal translation of the word senyawa would be 'chemical compound'. It's used to describe when two or more different elements combine and create something new. In this case it is my partner Wukir Suryadi and I who are the two different chemical elements. He stands for nature - which is represented by his bamboo instrument - and I represent the human. Senyawa is all about the relationship between man and nature.

Does it also represent the fusion in the music?

RSH: Yes of course, you can say that although maybe it is too easy, too simple. But that is essentially the idea.

When did you first meet?

RSH: In 2010. We jammed on stage for the first time in Yogyakarta, Indonesia. It was at the Yes No Klub. Wukir was playing there and I was introduced to him on stage by the promoter and jammed with him. So we jammed together in front of an audience before we became friends. And then just four days later we had our first EP - which can be downloaded for free from YesNoWav.com. We decided to record an EP straight away. After the show we had a day off and then we played non-stop so we had our first EP four days later. And we've played intensively ever since.

Can you tell me how much training you underwent to be able to sing like you do now?

RSH: I didn't go to any music school, I didn't have a musical teacher or any training, so none. I practice singing in my spare time. The way I sing is this - I just decide that I want to sing so I sing. I find the process to be very releasing. The practice is the jam session. So in a jam session or improv session I usually start to find new ways of singing and little by little I add to my register. I'm always very keen to do jam sessions and improv because that is my learning process.

Given the amazing range of sounds the bamboo instrument can create, do you feel it necessary to have as much of a range with your voice, for the balance of the music?

RSH: That's the point. When I first saw Wukir with the bamboo instrument, I was like, "wow". It is such a versatile instrument. I can produce all kinds of sounds but one thing the instrument lacks is the human voice. So I was like, "Ah! I will collaborate with this guy but I won't play any instrument, I will just sing. But how will I match him?" So I had to try my best to try and create the same level of diversity.

The bamboo instrument is very unique. Can you tell us about it - how long it took to make, what kind of register it has?

RSH: It was made by trial and error. It took a year to make the first one - the one that he uses today. It consists of many metal strings and then bamboo skin, also used as strings. When he plucks the latter it makes a percussive sound. The thing that I love the most about it is it has metal strings which can sound like a harp, but at the same time he can play the percussive sound, which is made out of the bamboo skin itself.

It has a specific ritual shape doesn't it?

RSH: The shape is an interesting thing. When we were still colonised by the Dutch up until 1945, people didn't have guns or proper weapons to fight with, so the weapons we used were sharpened bamboo spears.

What about the languages you sing in?

RSH: Mostly Bahasa Indonesian but other traditional languages as well, like Javanese… I never want to use English, just our traditional languages or just noise… just Dada.

Can you tell me how Senyawa fit into the idea of Indonesian traditional music? For example, how do people from your parents' generation view the music that you make?

RSH: Most of them don't like it. They think it's too weird, too experimental and too contemporary. But then the young people think it's too traditional! So most of them don't like our music… it's very hard! [laughs] This is why we usually play outside of Indonesia. People in Europe or Australia are more educated in terms of music so they know how to appreciate music like this. In our country young people mostly are educated to appreciate music by referencing it to something they already know. "I like this because it reminds me of Metallica!" But with something like this they will say it is too traditional.

What are the main lyrical themes of Senyawa? What do you actually sing about?

RSH: Mostly about how nature and humanity interact. For example we sing about a volcano which erupted in 2010 and wiped out the next village to mine. Most of the songs represent each element. So one song will represent the element of fire and another will represent the element of water for example.

Can you tell me about the first tour of Australia? What sort of people were coming to see you and how exciting was it for you?

RSH: The first time we went to Australia we really owed a favour to our manager Kristi Monfries, she saw us and said she would bring us there. We played at a fairly big jazz festival in Melbourne and it was our first time abroad. She organised the tour around that time. And that was the first time I realised that we would be more appreciated outside of Indonesia… because we never had that kind of appreciation outside of Indonesia. After that, we just wanted to go away more and more and more…

So to my ears, as well as being avant-garde and - from the little I know - Indonesian in style, the thing that Senyawa reminds me of the most is heavy metal. Do you think there is an influence of heavy metal on what you do?

RSH: [EMPHATICALLY] Yes. Both of us grew up as teenagers listening to Sepultura and Slayer and all of those bands. And for me, I stopped listening to metal ten years ago, but when I was a teenager I listened to it like crazy. But even though I stopped listening to metal it's already in me. I can't eliminate it. Wukir as well. So when people ask me what kind of music do Senyawa make, I always say: "It's metal."

What was it like playing with Keiji Haino?

RSH: We toured Japan last year and one of the shows was an improv night and we challenged all of these Japanese legends to play with us. Keiji Haino. Tatsuya Yoshida from Ruins. Kazuyuki Kishino of KK Null… they all came on stage one by one and played with me and then again with Wukir and then again with Senyawa… so it was a very long night for us! We're making a DVD of it.

Have either of you studied Indonesian music?

RSH: No. Neither of us have studied music. My background is literature and Wukir's background is theatre.

Can you tell me a bit about making the film, Calling The New Gods, with Vincent Moon?

RSH: We shot that whole film in one day with no crew… just a driver and the director. It was a very exhausting day. So we'd select a location and then stop and improvise there using one tiny amp.

There's a track you play in the film where the bamboo instrument is mimicking the sound of Big Ben and it sounds like a train building up speed…

RSH: There is a children's song about a train and I used the lyrics of that song, but I changed the music completely. So using the children's song lyrics about public transport in Indonesia, but we transformed it into some kind of new song.

Was there an important political decision to look inwards towards Indonesia and to reject Western culture of pop and rock?

RSH: It's not actually rejecting the West but it is about making people realise that traditional music is something that is out there and not completely uncool. Young people of our age mainly refuse traditional music. It is seen as very uncool. Many people have tried to combine modern music with traditional music - so they make rock music or jazz and then put an element of traditional music in there - some gamelan or Indonesian singing, but I don't think it will work like that, you know? So by making it one instead of two; by bringing it together, that is how we do it.

And I really like the improvised record you did with Arrington de Dionyso. How did that come about?

RSH: Arrington, as you know, loves Indonesia. The first time he toured here he toured with Senyawa and the following year he came back and said he wanted to do a record with us. So we just did a record in Wukir's house. He's American but it's also him throat singing on that record. The reason why we want to make an album with him is [while] we know he's American we can't even sense that in him. It's good.

What's next for Senyawa?

RSH: We have a lot of tours scheduled and a lot of records coming out this year. We are recording with Uchihashi Kazuhisa [of Ground Zero]. There will be new albums with new instruments as well. I am also trying to extend Senyawa… I have my own choir project. I created a system so people can improvise while singing in a choir. So on the new Senyawa album, Wukir will be playing music, but I won't be singing, I'll be conducting a choir who will be singing as if I was singing.

Menjadi is out now on Morphine Records. Senyawa play Cafe OTO in London on September 7; head here for full details and tickets