iOS Musician Apps (140) Supported Technologies is Audiobus, Instrument Type is Synth

BLEASS Granulizer generates short samples (‘grains’) from different input signals by modulating different parameters which you can visualize thanks to a 3D Visualizer.

GarageBand is a DAW by Apple.

Groove Rider GR-16 is a professional step-sequenced groove box, inspired by professional hardware drum machines and rhythm boxes.

Poison-202 is a professional Vintage Midi Synthesizer.

Pure Acid is a bassline synthesizer and drum machine in one app.

SquareSynth is a hybrid analog/8bit style synthesizer. It takes features from the NES console, and the Commodore 64 personal computer.

SpringSound is a physical-modeling audio synthesizer that produces sounds by simulating interactions and vibrations of a set of activators and masses connected to springs.

Just a Toy Synthesizer. Included: 2 Oscillators, LPF, Delay effector, Ribbon controller.

KQ MiniSynth is a polyphonic modular synthesizer.

KQ Dixie is a 6-Operator FM synthesizer that is modeled on the synthesizer which appeared on the 1980s.

Lagrange synthesizer has two oscillators, a noise generator and two filters that can be selected from various algorithmic models.

Mersenne is a melodic percussion synthesizer that combines two FM synthesis modules, a noise generator and a resonator.

Redshrike is a polyphonic synthesizer that combines a resonator designed to make more complicated sound creation and subtraction synthesis with an FM oscillator that creates violent distortion.

Lorentz is not only a live-oriented analog modeling synthesizer, but also has a resonator that makes metallic and aggressive sounds.

Laplace is a physical-modeling synthesizer based on resonator synthesis that makes it easy to create bowed string, plucked string, blown pipe and metallic sounds.

Attack Drums is a synthesizer designed mainly for drum sounds, but the powerful sound engine can also be used for everything else - including vocals.

Flexible and powerful frequency generator.

Wotja X is a new cross-platform interface for the 'Wotja Generative Music System'.

AudioKit Synth One is a completely free & open-source professional iOS Synthesizer. 

Combine 3 oscillators and a noise envelope to produce bright 80s-style synths, deep rich bass, punchy kicks and snares, a variety of screaming leads, and even breathy percussion.