The BioSync interface presented in this paper merges the heart-rate basedparadigm with the brain-wave based paradigm into one mobile unit which isscalable for large audience real-time applications. The goal of BioSync is toprovide a hybrid interface, which uses audience biometric responses foraudience participation techniques. To provide an affordable and scalablesolution, BioSync collects the user’s heart rate via mobile phone pulseoximetry and the EEG data via Bluetooth communication with the off-the-shelfMindWave Mobile hardware. Various interfaces have been designed and implementedin the development of audience participation techniques and systems. In thedesign and concept of BioSync, we first summarize recent interface research foraudience participation within the NIME-related context, followed by the outlineof the BioSync methodology and interface design. We then present a techniquefor dynamic tempo control based on the audience biometric responses and anearly prototype of a mobile dual-channel pulse oximetry and EEG bi-directionalinterface for iOS device (BioSync). Finally, we present discussions and ideasfor future applications, as well as plans for a series of experiments, whichinvestigate if temporal parameters of an audience’s physiological metricsencourage crowd synchronization during a live event or performance, acharacteristic, which we see as having great potential in the creation offuture live musical and audiovisual performance applications.