Digitally controlled active noise reduction with integrated speech communication

Active noise reduction is a successful addition to passive
ear-defenders for improvement of the sound attenuation at low frequencies.
Design and assessment methods are discussed, focused on subjective and objective
attenuation measurements, stability, and high noise level applications. Active
noise reduction systems are suitable for integration with an intercom. For this
purpose the intelligibility in combination with environmental noise is
evaluated. Development of a system includes the acoustical design, the (digital)
feedback control, and the speech input facility. In order to achieve optimal
performance a specific audio design is required. An example of such a
development is discussed.