The first thing that strikes you about this iPhone synth is the GUI design. A small button at the top left switches between the configuration pages - pressing it momentarily flips to the next page, dragging it scrolls. There are pages for sound generation, adding motion control, global parameters, live playback and sequencer.
Parameter editing is cleverly arranged to make the most of two-handed input. A virtual scroll wheel on the right fits neatly under your right thumb, while a trigger pad on the left can be used to instantly play the sound. Holding this trigger doesn't sustain the sound for some reason, and there's no way of editing a sound while playing an arpeggio or a sequence.
The three-voice synth engine is great, especially for low-frequency saw-based tones. Its ability to work polyphonically makes it much better suited to gated strings and evolving pads than its competitors, and it includes some excellent routing possibilities for frequency, ring and phase modulation. You can switch between editing the parameters for the two oscillators, three two-stage envelopes, single filter or comprehensive modulation options.
Each set of parameters appear as a list of sliders below the buttons, and while they're easy to modify, the program doesn't seem to recognise more than two touches at a time. If you need more control, you can use the extensive modulation options to manipulate parameters using tilt control or the control envelope in the sequencer.
The 16-step sequencer includes trigger probability and swing, but the note selection would be far more effective if it used the same hold and drag motion of the mode selector. We'd also like a random mode for arpeggiator. There's no pattern sequencing either, which is a clear indicator that bleep!Synth is intended as a real-time performance partner to its compositional sibling bleep!Box.
The highlight of this app is the user-defined matrix of the Play mode. Notes are triggered from a grid of buttons, and when combined with one of the 21 different scales on offer, the output can sound unusual and fantastic.