Assemble's synthesiser features four bandlimited oscillators, each with eight voices of polyphony, a 16x oversampled tempo-synchronised stereo delay effect, and a vibrato effect. The parameters of each oscillator and each audio effect can be modified easily in real-time.

The synthesiser can be played by sequencing patterns of notes with Assemble's sequencer. Notes can be sequenced using a computer keyboard and mouse, or alternatively using Assemble's on-screen keyboard. A sequence can include as many as eight sixteen-step patterns, which can be played discretely in Pattern Mode or sequentially in Song Mode. Once a sequence is complete, it can be named and saved locally on your device.

Assemble can record audio and generate video clips from recorded audio for sharing. Each video clip adapts to Assemble's visual theme and features one of two audio visualisations: a standard waveform plot, or a Lissajous figure.