Feedback Delay Line Research Articles

Echo Shaping Using Sums of Damped Complex Sinusoids

Feedback delay lines are the basis of myriad audio effects and reverberation schemes. The feedback delay line, by itself, is limited to producing an infinite sequence of exponentially decaying echoes. We introduce a new type of linear time-invariant echo effect whose impulse response is a generalized sum of damped complex sinusoids. This permits echo responses to be shaped as simple sinusoids, Fourier-based waveforms, and many other complex, possibly nonperiodic, patterns that would not be feasible with other existing methods. Additionally, because the response is complex-valued, it can be used to produce auto-panning echo effects with many kinds of spatial trajectories. The effect is computationally efficient and straightforward to implement, as it only requires a parallel combination of feedback delay lines.

Carrier-free radar signal design with MTI Doppler processor

Doppler processors with feedback delay line circuits can produce thumbtack range-velocity resolution functions by processing carrier-free radar signals consisting of a large number of characters. The moving target indicator (MTI) Doppler processor, which is a generalisation of the two-pulse canceller circuit, can produce thumbtack range-velocity resolution functions by processing only two characters of the received signal, provided that each character has a correlation function with a main lobe and no time sidelobes. The two-pulse canceller circuit is modified to produce maximum output when the pulse separation time of the returned signal, from a stationary or moving target, is identical with the delay time of the MTI circuit, whereas conventional MTI produces no output in such a case. The processor is analysed in terms of the time difference between the Doppler shift of the received signal and the Doppler time of the processor. Blind speeds defined for MTI response to sinusoidal carriers do not exist in the output of the MTI Doppler processor. Sidelobe-free thumbtack range-velocity resolution functions for signal characters with beta time variations are presented. The two-pulse canceller circuit is analysed for returned signals from extended targets.