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Acoustic Signals and Audio Systems
Published in Francis F. Li, Trevor J. Cox, Digital Signal Processing in Audio and Acoustical Engineering, 2019
A system is said to have memory if the output from the system is dependent on the past inputs to the system. A system is said to be memoryless if the output is only dependent on the current input. Memoryless systems are the easiest to work with since simple algebraic equations are adequate to describe their behaviours, but systems with memory are more common in signal processing applications. A memory system is also called a dynamic system, whereas a memoryless system is also called a static system. Memory stems from energy storage in the system. Mechanical systems with mass and springs, electronic systems with capacitors and inductors, and digital systems with delay units all have memories. Differential equations for analogue systems or difference equations for digital systems are needed to describe the dynamic behaviours of such systems.
Convolution
Published in Nassir H. Sabah, Circuit Analysis with PSpice, 2017
Pulses occurring at λ < t are “past” inputs whose contributions are summed by the integration to obtain the total response at time t. The contributions of these pulses are weighted by the impulse response h(t − λi). It is seen from Figure 20.32a that this weighting depends on the shape of the impulse response. Because of the exponential decay of the impulse response shown, pulses occurring over part ‘ab’, shown crossed in Figure 20.32a, have more weight than pulses occurring earlier in time, over the part ‘bc’. The contributions of pulses occurring at λ < t can be interpreted as a kind of “memory” possessed by the circuit, in the sense that past inputs are not “forgotten”, since they affect the output at the present time t. If the impulse response is itself an impulse (Figure 20.32b), the circuit is “memoryless” in the sense that the present output depends only on the present input. On the other hand, a circuit whose impulse response is a step function (Figure 20.32c) has “perfect memory” in the sense that past inputs are not only remembered, but their contributions to the present input are equally weighted.
Algorithm/Architecture Coexploration
Published in Ling Guan, Yifeng He, Sun-Yuan Kung, Multimedia Image and Video Processing, 2012
Gwo Giun (Chris) Lee, He Yuan Lin, Sun Yuan Kung
In the theory of signals and systems, a system is said to be memoryless if its output depends on only the input signals at the same time. However, in visual computing applications such as video coding and processing, some intermediate data have to be stored in memory depending on the dataflow of algorithms in higher abstraction levels. Consequently, in order to perform the appropriate algorithmic processing, data storage must be properly configured based on the dataflow scheduling of the intermediate data. Hence, the algorithmic storage configuration is another essential intrinsic complexity metric in AAC design methodology, which is transparent to either software or hardware designs. For software applications, the algorithmic storage configuration helps design the memory modules such as cache or scratch-pad and the corresponding data arrangement schemes for the embedded CPU. In hardware design, the immediate data can be stored in local memory to satisfy the algorithmic scheduling based on this complexity metric.
Prediction-based control for LTI systems with uncertain time-varying delays and partial state knowledge
Published in International Journal of Control, 2018
V. Léchappé, E. Moulay, F. Plestan
A vast literature is available for the control of input-delay systems. The works on this topic can be divided into two main classes according to the controller design: memory-free (or memoryless) and memory controllers. The interest of memory-free controllers is that they are easier to implement in practice. The truncated predictor feedback is an example of such a technique; see Zhou, Lin, and Duan (2010) for constant delay and Yoon and Lin (2013), Zhou, Lin, and Duan (2012) and Zhou and Lin (2014) for time-varying delays. Sliding mode and adaptive control have also been used in Richard, Gouaisbaut, and Perruquetti (2001) and Choi and Lim (2006), respectively. The drawback of memoryless control is that it is usually not possible to compensate for an arbitrarily long delay except for some particular classes of systems as in Mazenc, Mondié, and Niculescu (2003), Mazenc, Mondié, and Francisco (2004) and Lin and Haijun (2007).