# Number of source estimation knowledge sources¶

This section focuses on implementation of knowledge sources for the estimation of active sound sourcs in an auditory scene within the blackboard framework.

## Number of Sources knowledge source: NumberOfsourcesKS¶

Objects of class NumberOfsourcesKS implement models, by incorporating an instance of a model (which has to implement the models.Base interface) with knowledge about the relationship of auditory cues and the number of active sound sources. The model gets loaded from directories you specify upon construction, and should be created with the Estimating the Number of Sound Sources. The model object of NumberOfsourcesKS can employ any kind of model, such as a linear support vector machine, or a Gaussian mixture model. The NumberOfsourcesKS needs access to Auditory front-end signals, thus it is a subclass of AuditoryFrontEndDepKS (see Section Auditory signal dependent knowledge source superclass: AuditoryFrontEndDepKS). The model object holds the signal request structure.

The knowledge source predicts, based on the incorporated source model the number of active sound sources in the currently received auditory stream.

 binds to AuditoryFrontEndKS.KsFiredEvent reads data category locationHypothesis (otherwise sourcesAzimuthsDistributionHypotheses) possible also identityHypotheses if required by the model’s feature creator (see :ref:sec-amlttp-select-features) writes data category NumberOfSourcesHypotheses triggers event KsFiredEvent