Aside from vocals, the first guest EP on Old Apparatus's Sullen Tone label doesn’t differ from the singles that launched the murky London bass collective's imprint last year. Awash with crackling, fuzzy low-end and decayed beats, Khing Kang Kong - made of Old Apparatus pianist LTO and cult rapper Mowgli - stay close to the handrail established by their parent group. But it’s precisely these vocals that make IAO such an intriguing listen: rather than rhyme, Mowgli spits out stream-of-consciousness thoughts into hulking melodies and clanking beats whipped up by LTO. The unlikeliness and impact of Khing Kang King's sound confirms why the Sullen Tone label quickly became so covetable, and pushes the collective's signature sound into a strange and rewarding new place.

Old Apparatus' traits are prominent from the start: glowering bass; moody, masculine piano textures and percussion like a tour round a blacksmith’s forge. Opener ‘Gone To Seed’ launches into slipping levers and Mowgli’s diagonal, jarring lyrics: “Diddley-squat/Serendipity/You’re shitting me,” spits the rapper, working himself into such a lather that on the lighter ‘Morning On Mercury’ his voice is vocodered and drowsy, as though the first track’s left him breathless. Here, creepy, three-note piano and reversed drums suck up the air, while the equally sorry ‘Front Page Expression’ blends sad guitars and arctic white noise, Mowgli’s anecdotes of “Stuffed crust lips/Glaring E numbers/Smear swine spit/Fountains of blood” spilling out like a bum describing his city.

One track shows just how ferocious LTO and his lyricist can get: the fast-paced ‘Metal On Ox Tongue’. Mowgli’s voice cries out a processed “Girl/Drop gold” before things lurch into a rush of mournful noise, ripping fabric, Theremins and dark, lunging beats. The rapper's shopping list delivery is like word association with a gangbanger, and as he darts through what could be a story of a club shooting - or a description of a butcher’s shop window - the track ruptures, grinds and scrapes, volatile as a tectonic fault line. On the surface, it may only be a slight departure from Old Apparatus' production style, but it confirms Sullen Tone as one of London's most pioneering labels, committed to pushing the barriers of bass music.