filter length

[yunzqq]

what does the filter length represent?

[boeddeker]

I don't get your question. In Section 4.4 in our paper [1] we describe the filter.
Alternatively, you could read the paper about BSSEval from Emmanuel Vincent [2].

[1] https://arxiv.org/pdf/2011.15003.pdf
[2] Vincent, Emmanuel, Rémi Gribonval, and Cédric Févotte. "Performance measurement in blind audio source separation." IEEE transactions on audio, speech, and language processing 14.4 (2006): 1462-1469.