Olfactory interfaces synthesize odorants from a digital signature. They consist of a palette of odorants, a flow delivery system, and a control algorithm that determines the mixing ratios, concentration and timing of the stimulus. The palette stores odorants in either gel or microencapsulated form, and the diffuser is typically a set of nozzles equipped with microvalves or ink jet printer nozzles that release gels or liquid droplets by means of electrostatics or heat. A full interface also recognizes odors given off by users.