iOS Musician Apps (117) Supported Technologies is Inter-App Audio (IAA), Instrument Type is Synth

GarageBand is a DAW by Apple.

Xynthesizr is a streamlined yet capable 32-step matrix sequencer/monotimbral synthesizer with generative features and MIDI.

mood is a personal interpretation of the legendary Analog Synthesizer by Eugenio Giordani

Multilevel Interactive Sound Synthesizer. Up to 240 Frequency Modulation Oscillators or simple Wavetable Additive.

Pixound provides a deep musical experience that lets you instantly create music using any picture.

Tardigrain is a granular synthesizer. Sounds are created by taking smaller fragments of a sample and playing them back in a non linear fashion, with settings for grain size, direction, step size and more.

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

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

Moebius Lab is a multimorphic sound processor which contains a synth, a varispeed stereo sample player, effects and LFOs that can modulate each parameter.

Pure Synth® Platinum is a full-blown rompler/synthesizer for your iOS device. Neither the synth engine or the sample engine is an afterthought: Both engines are fully capable and feature-rich. The romper section contains a well rounded assortment of analog, synth, string, digital, and acoustic instruments.

iPhilicorda is an emulation of a vintage organ from the sixties, the Philicorda, created by the Dutch company Philips.

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.

The hybrid synthesis algorithm on which Addictive Pro is based provides you with efficient means for easy control of complex sounds far beyond usual sound synthesis methods.

For all creatures in the ocean of sound - Sonic textures from other worlds, Analog signature sounds,  Cut-through-the-mix leads and silkily smooth pads.

Additive synthesis is a sound synthesis technique that creates timbre by adding sine waves together. The timbre of musical instruments can be considered to consist of multiple harmonic or inharmonic partials or overtones.

Designed to deliver authentic dub sounds and effects, iTALIZER at it's heart is a monophonic synthesizer paired with an authentic tape echo emulation.

VOLT is a virtual analog synthesizer designed to create classic synth sounds while emphasising expressive play.

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.