The purpose of the Auditory front-end is to extract a subset of common auditory representations from a binaural recording or from a stream of binaural audio data. These representations are to be used later by higher modelling or decision stages. This short description of the role of the Auditory front-end highlights its three fundamental properties:
- The framework operates on a request-based mechanism and extracts the subset of all available representations which has been requested by the user. Most of the available representations are computed from other representations, i.e., they depend on other representations. Because different representations can have a common dependency, the available representations are organised following a “dependency tree”. The framework is built such as to respect this structure and limit redundancy. For example, if a user requests A and B, both depending on a representation C, the software will not compute C twice but will instead reuse it. As will be presented later, to achieve this, the processing is shared among processors. Each processor is responsible for one individual step in the extraction of a given representation. The framework then instantiates only the necessary processors at a given time.
- It can operate on a stream of input data. In other words, the framework can operate on consecutive chunks of input signal, each of arbitrary length, while returning the same output(s) as if the whole signal (i.e., the concatenated chunks) was used as input.
- The user request can be modified at run time, i.e., during the execution of the framework. New representations can be requested, or the parameters of existing representations can be changed in between two blocks of input signal. This mechanism is particularly designed to allow higher stages of the whole Two!Ears framework to provide feedback, requesting adjustments to the computation of auditory representations. In connection to the first point above, when the user requests such a change, the framework will identify where in the dependency tree the requested change starts affecting the processing and will only compute the steps affected.