Pitch Trajectories Research Articles

A multiband excited waveform-interpolated 2.35-kbps speech codec for bandlimited channels

Following a brief portrayal of the activities in 2.4-kbps speech coding, a wavelet-based pitch detector is invoked, which reduces the complexity of conventional autocorrelation-based pitch detectors, while ensuring smooth pitch trajectory evolution. This scheme is incorporated in a waveform-interpolated codec, which uses voiced-unvoiced (V/U) classification, and instead of simple Dirac pulses, an unconventional zinc basis function excitation is employed for modeling the voiced excitation. The required zinc-function parameters are determined in an analysis-by-synthesis loop, and for the sake of smooth waveform evolution and reduced complexity, a focused search strategy and a few further suboptimum restrictions are imposed without seriously affecting the speech quality. This baseline codec operates at a rate of 1.9 kbps, but it suffers from slight buzziness during the periods of excessive voicing. This impediment is then mitigated by invoking a mixed V/U multiband excitation, which slightly increases the bit rate to 2.35 kbps due to the transmission of the 3-b voicing strength code in each of the three excitation bands.

Abort landing guidance trajectories in the presence of windshear

The problem of flight trajectories in the presence of windshear is discussed. The abort landing problem is considered with reference to flight in a vertical plane. It is assumed that, at the windshear onset, the power setting is increased at a constant time rate until maximum power setting is reached; afterward, the power setting is held constant. Hence, the only control is the angle of attack. Inequality constraints are imposed on both the angle of attack and its time derivative. Optimal trajectories are considered. The performance index being minimized is the peak value of the altitude drop. Numerical results are obtained for several combinations of windshear intensities and initial altitudes. Guidance trajectories are considered, approximating the optimal trajectories, while using local information on the state of the aircraft and the knowledge of two scalar parameters: the initial altitude h 0 and the total wind velocity difference † W x . Simplified guidance trajectories are also considered, employing only local information on the state of the aircraft, while avoiding the use of wind measurements. Comparative numerical results are obtained for the optimal trajectories (OT), the guidance trajectories (GT), the simplified guidance trajectories(SGT), and some alternative trajectories [constant pitch trajectories (CPT) and maximum angle of attack trajectories (MAAT)].

Maximum survival capability of an aircraft in a severe windshear

This paper is concerned with guidance strategies and piloting techniques which ensure near-optimum performance and maximum survival capability in a severe windshear. The take-off problem is considered with reference to flight in a vertical plane. In addition to the horizontal shear, the presence of a downdraft is assumed. First, six particular guidance schemes are considered, namely: constant alpha guidance; maximum alpha guidance; constant velocity guidance; constant absolute path inclination guidance; constant rate of climb guidance; and constant pitch guidance. Among these, it is concluded that the best one is the constant pitch guidance. Next, in an effort to improve over the constant pitch guidance, three additional trajectories are considered: the optimal trajectory, which minimizes the maximum deviation of the absolute path inclination from a reference value, while employing global information on the wind flow field; the gamma guidance trajectory, which is based on the absolute path inclination and which approximates the behavior of the optimal trajectory, while employing local information on the windshear and the downdraft; and the simplified gamma guidance trajectory, which is the limiting case of the gamma guidance trajectory in a severe windshear and which does not require precise information on the windshear and the downdraft. The essence of the simplified gamma guidance trajectory is that it yields a quick transition to horizontal flight. Comparative numerical experiments show that the survival capability of the simplified gamma guidance trajectory is superior to that of the constant pitch trajectory and is close to that of the optimal trajectory. Next, with reference to the simplified gamma guidance trajectory, the effect of the feedback gain coefficient is studied. It is shown that larger values of the gain coefficient improve the survival capability in a severe windshear; however, excessive values of the gain coefficient are undesirable, because they result in larger altitude oscillations and lower average altitude. Finally, with reference to the simplified gamma guidance trajectory, the effect of time delays is studied, more specifically, the time delay τ1 in reacting to windshear onset and the time delay τ2 in reacting to windshear termination. While time delay τ2 has little effect on survival capability, time delay τ1 appears to be critical in the following sense: smaller values of τ1 correspond to better survival capability in a severe windshear, while larger values of τ1 are associated with a worsening of the survival capability in a severe windshear.

Efficient pitch estimation for speech and music

An algorithm for estimating wideband pitch trajectories of acoustic signals is described. Its software implementation is fast, and real-time operation can be achieved by using inexpensive hardware. Results are presented for representative speech and music signals.