Digital Noise Reduction (DNR)
DNR has been put forward by various manufacturers as a method to improve speech in noise [Fig1] by using algorithms to analyse the environmental acoustics and concentrate on speech signals.
Noise, such as that of a fan or air-conditioner can be characterised as being fairly steady in intensity over time. Speech, however rapidly fluctuates in intensity over time. This difference in amplitude modulation is what DNR algorithms attempt to use to determine if the incoming signal is speech or noise.
Unfortunately, because speech and noise in the same channel cannot be adjusted separately, there are currently no DNR systems that can effectively manage to improve speech understanding in situations where the babble is highly modulated (such as a room full of people talking). However, when used in conjunction with recommended listening strategies, DNR is seen to provide an inclination toward improved listening ease in select environments.
Digital Speech Enhancement (DSE)
Again using algorithms to try and identify the unique acoustic properties of speech, DSE provides more gain (increase in volume) and less compression when speech is present as opposed to DNR applying less gain in the presence of noise. Whilst DSE is no better than DNR at separating speech in noise but again does provide more listening comfort in background noise.