Tomoyasu Nakano Masataka Goto A spectral envelope estimation method based on F0-adaptive multi-frame integration analysis. 11-16 2012 SAPA@INTERSPEECH https://www.isca-archive.org/sapa_2012/nakano12_sapa.html conf/interspeech/2012sapa db/conf/interspeech/sapa2012.html#NakanoG12