Acoustic-space formulation

Two main, quite different, approaches to the target cost function have been proposed. The first, described in this section is called the independent feature formulation (IFF) and was proposed in the original Hunt and Black paper. Since then, many variations of this have been put forward but all can be described in the same general form. The second, described in Section 16.4, is termed the acoustic space formulation (ASF) and shares many similarities with the HMM systems of Chapter 15. The fact that there are only two main target function formulations is probably more due to historical accidents of system development than because these are particularly salient solutions to the problem. As we shall see, we can consider a more general formulation which encompasses both these and many other potential formulations. 

The acoustic space formulation (ASF) which uses the acoustie distanee between feature eom-binations to determine distance. A function is used to project from a feature combination to a point in acoustic space, and this function is normal trained from example data. A number of techniques can be employed to estimate this point in acoustic space for feature combinations unobserved during training. 

Section 16.4. The Acoustic Space Target Function Formulation... 

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