Abstract—In most applications of sinusoidal models for speech
signal, an amplitude spectral envelope is necessary. This envelope
is not only assumed to fit the vocal tract filter response as
accurately as possible, but it should also exhibit slow varying
shapes across time. Indeed, time irregularities can generate
artifacts in signal manipulations or increase improperly the
features variance used in statistical models. In this letter, a
simple technique is suggested to improve this time regularity.
Considering that time regularity is characterized by slowly
varying spectral shapes among successive frames, the basic idea
is to smooth the frequency derivative of the envelope instead
of its absolute value. Even though, this idea could be applied
to different envelope models, the present letter describes its
application to the simple linear interpolation envelope. Using real
speech signals, the evaluation shows that the time irregularity can
be drastically reduced. Additional experiments using synthetic
signals also show that the accuracy of the original envelope is
not degraded by the process.