The Ear Tone Toolbox is a free collection of instruments that evoke naturally generated tones in the ear. Called difference tones or auditory distortion products, the “ear tones” occur at separate frequencies from the provoking acoustic tones, sound as if they emerge from within the head, and are not physically present in the acoustic space. The instruments in The Ear Tone Toolbox produce the necessary acoustic frequencies for evoking difference tones with precision. The instruments control the two most prominent difference tones: the quadratic difference tone and the cubic difference tone.
The Ear Tone Toolbox contains instruments that are ready to use in a variety of software and hardware environments, as well as optional source code for compiling to other formats and platforms using the Faust and Cycling74 RNBO programming languages. The current version of the software consists of several instruments, each with multiple variations. The instruments can be used in most digital audio workstation (DAW) software such as Ableton Live, programming environments such as Max/MSP or Pure Data, or with hardware modular synthesis systems.
For more information, see The Ear Tone Toolbox for Auditory Distortion Product Synthesis, from the 2016 ICMC proceedings, or Chechile's dissertation Practical Applications of Difference Tones in Electronic Music Composition and Synthesis.
other platforms and previous versions here