Subjective ratings of instantaneous and gradual transitions from narrowband to wideband active speech

In advanced heterogeneous telecommunication networks, network resources can dynamically dictate the type of speech coding that is used. An increase in resources allows for lower coding distortion or it might also be used to provide wideband speech instead of narrowband speech. Existing studies have demonstrated that wideband speech is preferred to narrowband speech, but they have also demonstrated that an abrupt transition from narrowband to wideband is perceived as an impairment, even though it is a transition to a higher quality signal. We describe our recent work that resulted in subjective scores for abrupt and gradual transitions from narrowband to wideband at the midpoint of a six-second segment of active speech. On average, signals that start narrowband and end wideband are rated slightly lower than constant narrowband signals and results are nearly the same for abrupt and gradual (2.5 second) transitions. Scores from 20 listeners show a wide range of individual opinions so we conclude that studies of bandwidth transitions may be quite sensitive to the listener population sample.