[SRILM User List] Questions on conversion word lattice to mesh

[Максим Кореневский]

 Hi, all,

I use lattice-tool.exe to convert word lattices (in HTK-like SLF format) obtained from recognition pass into a word confusion networks (meshes). SLFs contains both acoustic and language model scores and lm_scale parameter (used by recognizer) in its header. Word insertion penalty was set to 0.

When I scale both acoustic and LM scores with a constant factor C, I see that the 1-best path through mesh depends strongly on it. When C is large the mesh 1-best sentence coincides to word lattice 1-best sentence (which is in turn recognizer 1-best output), but when C goes down to zero, WER of mesh 1-best sequence increases monotonically.
I believed that optimal value of this factor should be about 1/lm_scale (as proposed in several papers, for example, "Confidence measures for Large Vocabulary Speech Recognition" by F.Wessel et al., 2001), but I observe an average WER increase about 5% absolute over large number of files for such factor value.

Is it caused by incorrect use of lattice-tool for mesh generation or this situation is normal ?

Maxim.
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