Method for dynamic determination of time constants, method for level detection, method for compressing an electric audio signal and hearing aid, wherein the method for compression is used

#Compressors can be found in most modern hearing instruments. They provide a number of possible benefits for the hearing aid user:

#Loudness Compensation,

#the task of loudness compensation compressors is to crush the dynamics of the acoustical environment into the dynamics of the hearing impaired.

#FIG. 1 shows a block diagram of the simple feed forward compressor according to the prior art,

#FIG. 2 displays a block diagram of the level detector according to the invention,

#FIG. 3 shows a flow diagram of a version of the level detector according to the invention,

#The method for level detection according to the invention is displayed in FIG. 2. The input signal is analyzed in two parallel level detectors: an auxiliary level detector and a guided level detector. The time constant of the auxiliary level detector is fixed. The time constant of the guided level detector is determined by the dynamical analysis. The dynamical analysis is based on the output of the auxiliary level detector and the output of the guided level detector. The output of this analysis determines at all times the time constant of the guided level detector and thus the dynamical behavior of the level detector as a whole.

#In an embodiment of the invention, the auxiliary and the guided level detector are implemented as a simple level detector as shown in FIG. 4. In the simple level detector, the input signal is rectified and filtered by a first order IIR filter. The single coefficient f of this IIR filter is directly related to the time constant τ of the simple level detector by the following relations:

#τ = - 1 fs · log ⁡ ( f ) ⁢ ⁢ and ⁢ ⁢ f = ⅇ - 1 τ · fs .