1. An acoustic processing, device comprising: an interface for receiving acoustic features obtained from an input analog signal representing an incoming voice signal; a processing unit configured to calculate one or more current Hidden Markov Model (HMM) pruning thresholds; a histogram pruning unit configured to prune one or more current HMM states based on the one or more pruning thresholds to generate one or more active HMM states; a pre-pruning unit configured to prune the one or more active HMM states based on an adjustable pre-pruning threshold to generate active HMM states output of the pre-pruning unit, wherein the adjustable pre-pruning threshold is based on one or more prior pruning thresholds, and wherein the active HMM states output of the pre-pruning unit each indicate a phoneme of the incoming voice signal and are each associated with a HMM state score; and a senone scoring unit configured to provide a senone score to the pre-pruning unit, wherein the pre-pruning unit modifies the adjustable pre-pruning threshold based on the senone score wherein the pre-pruning follows the histogram pruning for a current frame the incoming voice signal and precedes the histogram pruning for a next frame, and wherein the interface transfers the phonemes and their associated HMM state scores to a further speech recognition stage and the further speech recognition stage generates recognized speech corresponding to the incoming voice signal.