Acoustic feedback is capable of driving an electroacoustic amplification system unstable. Inserting a frequency shifter into the feedback loop can increase the maximum stable gain before instability. In this paper, we explain how frequency shifting can effectively smooth out the feedback loop magnitude response, and how this relates to the system stability. Then we describe measurements on real...

Pitch shifting of polyphonic music is usually performed by manipulating the time-frequency representation of the input signal. Most approaches proposed in the past are based on the Fourier transform although its linear frequency bin spacing is known to be inadequate to some degree for analyzing and processing music signals. Recently invertible constant-Q transforms (CQT) featuring high Q-factor...

There have been many published studies aiming to identify temporal changes in river flow time series, most of which use monotonic trend tests such as the Mann–Kendall test. Although robust to both the distribution of the data and incomplete records, these tests have important limitations and provide no information as to whether a change in variability mirrors a change in magnitude. This study d...

Spectrum is a limited and precious resource in wireless communications. Effective spectrum utilization becomes more and more important because of the expeditious increase of demand for wireless communications. In principle, the dual-polarization frequency reuse system, which employs two orthogonally polarized electromagnetic waves to carry information, can double the system capacity. However, t...

Light being scattered back from external surfaces or optical components can affect the sensitivity of optical measurement systems such as interferometers. By modulating the optical path length in front of a critical optical component the noise contributions due to the scattered light can be shifted out of the frequency band of interest. An opto-mechanical phase shifter has been designed for thi...

One of the major challenges of employing a two-frequency (or two-wavelength) phase-shifting algorithm for absolute three-dimensional shape measurement is its sensitivity to noise. Therefore, three- or more-frequency phase-shifting algorithms are often used in lieu of a two-frequency phase-shifting algorithm for applications where the noise is severe. This paper proposes a method to use geometri...

Acoustic feedback is a well-known phenomenon in any electro-acoustical real-time system. Whenever the loop gain of a system exceeds 1 for any frequencies, the system becomes unstable: Feeding the amplified sound signal back into the microphone causes a penetrating whistle. Among others, one concept to reduce acoustic feedback is frequency shifting. The implementation of a frequency shifter is e...