16. An apparatus according to claim 14 , wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to select by defining the sub-feature units based on correlations within the feature.
16. An apparatus according to claim 14 , wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to select by defining the sub-feature units based on correlations within the feature. 17. An apparatus according to claim 16 , wherein the memory and computer program code are further configured to, with the processor, cause the apparatus to be tuned based on iterative conversion and training operations.