Answers from Old Apparatus read like communiques from a sinister cabal. Indeed, this is precisely what they are. Parts of this interview would probably be best enjoyed barked, staccato and at ferocious volume through a loudspeaker, like the teachings of a totalitarian regime.

Go hunting for clues about their activities and you'll soon find yourself in the darkest of territory. Their website is covered with soot-stained snapshots of long-dead aristocrats, some of whom have had their heads replaced by menacing, insectile machines. O.A (as they call themselves, keen on code-names and military economy) have mapped out an aesthetic which splices together sci-fi dystopia and Gothic industrial dereliction, aged, occult and futuristic at the same time, like Dreyer's Vampyr cut into Lang's Metropolis. Another page is backdropped by documents from an abandoned bureaucracy concluding with the words (all in fearsome block capitals): 'Special War Division, Old Apparatus, Agency Restricted.' Only a slender dossier exists on the agents themselves. There are four of them, two of whom are brothers, all remain anonymous and operation is based somewhere in East London.

Luckily this familiar sort of studied opacity is matched by a set of strange, enchanting releases. Consider the recordings: a set of jagged improvisations recorded in their living room and released surreptitiously on cassette, a concussive, sludge-heavy remix for Honest Jons' Shangaan Shake project, the burned-down house of 'Chicago' and the shell-shocked delirium of 'Zimmer'. They refuse to settle into any permanent shape, keen to elude any singular definition. A few elements remain constant: industrial din, black holes of bassweight (their first two releases came via supreme dubstep dread master Mala's Deep Medi label), eerie ambience and dark mechanical rhythm. Their latest releases on their own Sullen Tone label continue this commitment to expanding and unsettling any sense of a collective, consistent sound even further. Realise and the recently-issued Alfur comprise two parts of a trilogy (the third, Harem, is due for release in mid-November), each instalment made by a member of the group in isolation.

Speaking to the collective via email, their dossier is fleshed out - just a little - and even endowed with some human warmth. The 'O.A. world' comes sharply into focus. Old Apparatus know exactly what they're doing. Old Apparatus are in control.

As much as you wish to remain anonymous, could you comment on your musical pasts?

Old Apparatus: We have quite a diverse range of musical backgrounds between us. A hip-hop instrumentalist, influenced by a lot of early RZA, Madlib and Four Tet - hence our connection with the rapper Mowgli. A classically-trained pianist who has previously been involved in IDM and post-rock-influenced projects and a hardcore/metal guitarist that was very involved in the London DIY scene. It helps that all of us are completely open-minded musically: it means that these core elements come together to form what we create now in a very organic and natural way. Above all, though, we're good friends and that's probably the most important part of the journey we're on.

What are the pleasures of anonymity?

OA: Assurance that irrelevant and superficial matters concerning the individual are kept from distracting those necessary for the creative process to take place. It helps place the listener in the OA world as it takes away the distraction of the 'personalities' behind the music. The collective nature of the project is very important to us.

How do your surroundings influence your work? Space and emptiness feel significant but there's also a sense of chaos, especially on your recent 'Chernobyl' mixtape.

OA: We are regularly exposed to the contrast between the claustrophobic sensory overload of inner-city London and the relatively soothing space and greenery at the fringes of the city, where we live. Different mixes bring out different sides of this dualism. With the Chernobyl mixture, we used bits that weren't necessarily fitting into our releases but still wanted people to hear them, and it turned out pretty crazy. The mix we've done for you is along those same lines, albeit with other people's music. For this mix, we put some new and unreleased material from our friends in there. The first track by a Dead Forest Index - who have the most amazing vocals. Untilted - Untitled is from a friend who wishes to remain nameless, and forthcoming on Left Blank. And 'Overcast' from Bandshell (Hessle Audio) who has big things to come. If we're feeling it, it goes in.

The visual aspect of your work feels like something you take a lot of care over (you methodically construct, how does it correspond with your sound?)

OA: The visuals go hand-in-hand with the music in creating an immersive environment from within which we can operate. The formation of a self-contained world has always been the primary aim of OA.

What's especially interesting about ruins and decay?

OA: As things age, they develop character, experience and wisdom. These are naturally evocative qualities in things. We can learn a lot from the past as all mistakes have been made before.

Are all the recordings in this trilogy led by a separate conceptual approach or do things develop more naturally?

OA: It's quite natural. Old Apparatus really started from us sending ideas around to each other, be it music and art we were making, or just stuff we were into. Things would start from there. Our projects often exist in various manifestations that we are really satisfied that everything works as a whole.

How does the forthcoming Alfur EP link with the past and future releases in the trilogy?

OA: The trilogy as a whole presents three personal takes on different aspects of the OA universe, unlike the other records that were made collectively. Instead of existing on one record, the journey will unfold over the following months.

What's the dominant feeling in your music? Are you drawn to darkness?

OA: Many of the tunes have turned out quite melancholy and meditative. There are moments in records and mixes that get dark and twisted but we don't like to stay rooted in one place for place for too long, so we try to bring out something more positive or vice versa. There's all kinds of emotions being expressed. Nostalgia and hope are moods that we often try to provoke as they make a good contrast from the colder and darker moments. We often end up creating soundscapes that have an ambiguous and alien quality. A pessimist is never disappointed, though, we'd like to think there is a thread of hope that runs through even the darkest moments of our music.