1. A key determination system, comprising: a device for analyzing an audio datum, comprising: a semitone analyzer, which is implemented to analyze the audio datum with regard to a volume information distribution over a set of semitones; and a vector calculator, which is implemented to calculate a sum vector over two-dimensional intermediate vectors, wherein each intermediate vector is calculated for a semitone, based on the volume information distribution, or each intermediate vector is calculated for an element of a definition set, based on a distribution derived from the volume information distribution, wherein the definition set is based on the set of semitones, and to output an analysis signal based on the sum vector; wherein the audio datum comprises a time course, wherein the semitone analyzer is further implemented to analyze the audio datum with regard to a time course of the volume information distribution, and wherein the vector calculator is further implemented to calculate a time course of the sum vector and output an analysis signal which is based on the time course of the sum vector, based on the time course of the volume information distribution or a distribution derived from the volume information distribution; and a key determinator, which is coupled to the device and is implemented to generate a key signal indicating a key based on the analysis signal of the device and provide the same at an output.