1. Speech recognition system comprising an audio input unit arranged in a terminal and a speech recognizer, wherein the speech recognition system further comprises an adjustable speech recognition enhancer having a parameterizable pre-filtering unit, a parametrizable dynamic voice level control unit, a parametrizable noise reduction unit and a parametrizable voice level control unit, wherein the parameters of the paramizable pre-filtering unit, the parametrizable dynamic voice level control unit, the parametrizable noise reduction unit and the parametrizable voice level control unit are adjusted to the characteristics of the specific audio input unit and/or the characteristics of the specific speech recognizer of the speech recognition system for adapting the audio input unit to the speech recognizer.