  Spectral envelope is one of the most important features that characterize the
timbre of an instrument sound. However, it is difficult to use spectral
information in the framework of conventional spectrogram decomposition methods.
We overcome this problem by suggesting a simple way to provide a constraint on
the spectral envelope calculated by linear prediction. In the first part of
this study, we use a pre-trained spectral envelope of known instruments as the
constraint. Then we apply the same idea to a blind scenario in which the
instruments are unknown. The experimental results reveal that the proposed
method outperforms the conventional methods.
