Myself, Jenna Duerr, and Rachel Grace Kerr recently published an article documenting the main instrumental uses for Rivener, our mask-less air flow estimation and nasalance system. This device records audio and low-frequency pseudo-sound with microphones placed at the nose and mouth, separated by a baffle and placed in a Venturi tube to prevent that pseudo-sound from overloading the circuitry.  The device can record all the aspects of hearing-impaired speech without interfering with the audio quality of the speaker or requiring physical contact with the system.  If you want a detailed description of what the system can do, here is an unpublished “white paper” documenting the strengths and limitations of the system in detail.