Acoustical sensing by time delay spectrometry

Abstract

Active acoustical sensing should utilize signal modalities with sufficient degrees of freedom to identify range, range rate, and those higher derivatives necessary to identify object rotation, as well as potential spectral properties which could be used for signature analysis of specific objects in a field. In addition, the specular nature of acoustic relfection from smooth objects demands signal processing which has substantial dynamic range along with good noise immunity. It is also shown that time delay spectrometry (TDS) is a modality which meets these requirements. The principles of TDS are developed as they apply to its use as a phase-coherent spread-spectrum communication technique. A constant amplitude signal with programmable phase structure is used as acoustic stimulus. System response to that stimulus consists of an ensemble of delayed replicas with complex amplitude and phase modulation. This can be interpreted as a signal whose dimensionality is determined by the degrees of freedom in the programmable phase structure. Selective spatial filtering followed by mapping to a lower-dimensional space can bring the property of interest to a usable form. This includes the conventional time domain reponses (range, rate,…) and frequency domain responses (spectrum, cepstrum,…).

Improving Accuracy of Acoustic Signal Time-of-Flight Measurement

“…Oprócz tego obwiednia odbieranego impulsu w jego początkowej fazie narasta z ograniczoną szybkością [8,[10][11][12][13]. Typowy kształt początkowej części impulsu akustycznego o częstotliwości 10 kHz, odebranego z środowiska gazowego w oknie czasowym od 14 ms do 16 ms, przedstawiono na rysunku 2a [12].…”

AcMus: an open, integrated platform for room acoustics research

“…These methods offer a much better signal-to-noise ratio and allow for repeatability of tests, since they use predefined excitation signals. Two of these methods have been implemented in AcMus: the MLS (Maximum Length Sequency) and a newer method called LSF (Log Sweep FFT), that is based on TDS (Time Delay Spectrometry) [12].…”

“…Another approach to measure an impulse response is the Time Delay Spectrometry (TDS), which consists in aplying a sinusoidal signal with linearly varying frequency, and recording the output [12]. The Log Sweep FFT Method (LSF) [9,18] is an evolution of the TDS that uses a logarithmic sine sweep as excitation signal.…”

Time and Frequency Domain Measurements of Materials with High Ultrasonic Attenuation Using Time Delay Spectroscopy

“…The capabilities of this technique and its profound theoretcial significance has been demonstrated for audio signals (especially for loudspeaker testing [4], by R. C. Heyser, who invented the technique [10]. Commerical TDS systems are available in the frequency ranges to 30KHz (Crown Electronics, 171R W. Mishawaka Road, Elkhart, Indiana, 465417), and to 200 KHz (Bruel and Kjaer, Marlborough, Massachusetts,…”