Fundamental frequency

About: Fundamental frequency is a research topic. Over the lifetime, 8941 publications have been published within this topic receiving 131583 citations.

Exploring the temporal mechanism involved in the pitch of unresolved harmonics

Abstract: This paper continues a line of research initiated by Kaernbach and Demany [J. Acoust. Soc. Am. 104, 2298–2306 (1998)], who employed filtered click sequences to explore the temporal mechanism involved in the pitch of unresolved harmonics. In a first experiment, the just noticeable difference (jnd) for the fundamental frequency (F0) of high-pass filtered and low-pass masked click trains was measured, with F0 (100 to 250 Hz) and the cut frequency (0.5 to 6 kHz) being varied orthogonally. The data confirm the result of Houtsma and Smurzynski [J. Acoust. Soc. Am. 87, 304–310 (1990)] that a pitch mechanism working on the temporal structure of the signal is responsible for analyzing frequencies higher than ten times the fundamental. Using high-pass filtered click trains, however, the jnd for the temporal analysis is at 1.2% as compared to 2%–3% found in studies using band-pass filtered stimuli. Two further experiments provide evidence that the pitch of this stimulus can convey musical information. A fourth experiment replicates the finding of Kaernbach and Demany on first- and second-order regularities with a cut frequency of 2 kHz and extends the paradigm to binaural aperiodic click sequences. The result suggests that listeners can detect first-order temporal regularities in monaural click streams as well as in binaurally fused click streams.

A Current-Source-Converter-Based High-Power High-Speed PMSM Drive With 420-Hz Switching Frequency

Abstract: In this paper, a current-source-converter (CSC)-based high-power high-speed (HPHS) permanent-magnet synchronous motor drive is proposed for high-speed compressor applications. The most important feature of the proposed CSC-fed HPHS drive is that the switching frequency is limited to 420 Hz at 200-Hz fundamental frequency. In the drive system, the whole operation range is divided into three regions, namely, the high-, medium-, and low-speed regions, where different modulation strategies and control schemes are used with the requirement of switching frequency and output filter. In particular, a two-pulse space vector modulation with dynamic capacitor voltage control is proposed for the high-speed region to achieve better dynamic and harmonic performance. Both simulation and experiments verify the proposed control strategy.

Radiation from a Josephson STAR-emitter

Abstract: We calculate the angular dependence of the radiation-zone output power and electric polarization of stimulated terahertz amplified radiation (STAR) emitted from a $dc$ voltage applied across cylindrical and rectangular stacks of intrinsic Josephson junctions. During coherent emission, a spatially uniform $ac$ Josephson current density in the stack acts as a surface electric current density antenna source, leading to an harmonic radiation frequency spectrum, as in experiment, but absent in all cavity modesl of cylindrical mesas. Spatial fluctuations of the $ac$ Josephson current cause its fundamental mode to lock onto the lowest finite energy cylindrical cavity mode, causing it to resonate, leading to a non-uniform magnetic surface current density radiation source, and a non-trivial combined fundamental frequency output power with linear polarization We also present a model of the superconducting substrate, and present results for rectangular mesas.

A new pattern of instability observed in an annular combustor: The slanted mode

Abstract: In annular combustion chambers of aero-engines and gas turbines, acoustic coupling may arise from azimuthal modes which are less well damped than axial modes. Also, since the circumference is the largest length in the combustor, the azimuthal modes have the lowest resonance frequencies and are most prone to instability. Such a coupling raises many scientific issues which are considered in a small number of fundamental experiments. The present investigation focuses on this problem and provides experimental data on a special type of combustion instability in which the thermo-acoustic resonant coupling involves a combination of modes. This produces an unusual pattern of flame responses in which the distribution of heat release rate is slanted. Data are provided in the form of free radical light intensity patterns (interpreted as heat release rate distributions) and microphone signals detected in the plenum and chamber. It is shown that the slanted pattern is the signature of a combination of two modes with coinciding frequencies, the first being a standing azimuthal mode while the second is an axial mode. Measurements of the flame describing function on a single matrix burner at the fundamental frequency are used to explain the observed phase shift and amplitude in the flame responses of the different injectors in the annular combustor.