List #4 Digital Synthesis and Spectral Analysis …
Fourier analysis is used in image processing in much the same way as with one-dimensional signals. However, images do not have their information encodedin the frequency domain, making the techniques much less useful. For example,when the Fourier transform is taken of an signal, the confusing timedomain waveform is converted into an easy to understand frequency spectrum. In comparison, taking the Fourier transform of an image converts thestraightforward information in the spatial domain into a scrambled form in thefrequency domain. In short, don't expect the Fourier transform to help youunderstand the information encoded in images.
Fourier Analysis and Synthesis - ResearchGate
Interferometry is an astronomical technique by which the signals from several instruments are combined to simulate an aperture-masked larger telescope. The signal from such an array is then deduced from studying the interference patters from the superposition of the combined waves. The signal is best expressed as a function that can be transformed into the Fourier domain and allows for the deduction of the signal phases. These transformed signals can then be correlated and by scanning through the signal to create an entire picture consisting of these transformed points. The inverse Fourier transform of this signal then restores this image, completing the process of aperture synthesis. I will briefly go over the optical physics of such a process, as well as demonstrate and explain in depth this type of data analysis on a real image.
We report studies on the synthesis of gold nanorods by a three-step seeding protocol method using a variety of different gold seeds. The synthetic method is adapted from one we published earlier (Jana et al. 2001, , 4065). The seeds chosen for these studies have average diameters in the range from 4 to 18 nm, with positively charged as well as negatively charged surface groups. In all the cases, along with a large concentration of long rods, a small number of different shapes such as triangles, hexagons, and small rods are observed. The proportion of small rods increases with an increase in the seed size used for nanorod synthesis. For long nanorods synthesized by different seeds a comparison of various parameters such as length, width, and aspect ratio has been made. A dependence of the nanorod aspect ratio on the size of the seed is observed. Increasing the seed size results in lowering of the gold nanorod aspect ratios for a constant concentration of reagents. The charge on the seed also plays a role in determining the nanorod aspect ratio. For positively charged seeds variation in the aspect ratio is not as pronounced as that for negatively charged seeds. The gold nanorods synthesized were characterized by transmission electron microscopy (TEM), UV−vis spectroscopy, and Fourier transform infrared spectroscopy. The role of seed size in the size and shape evolution of the nanocrystal, at different growth stages, has been studied by TEM.
also called Fourier synthesis, ..
One of the important ideas for sound reproduction which arises from Fourier analysis is that it takes a high quality audio reproduction system to reproduce percussive sounds or sounds with fast transients. The sustained sound of a trombone can be reproduced with a limited range of frequencies because most of the sound energy is in the first few harmonics of the fundamental pitch. But if you are going to synthesize the sharp attack of a cymbal, you need a broad range of high frequencies to produce the rapid change. You can visualize the task of adding up a bunch of sine waves to produce a sharp pulse and perhaps you can see that you need large amplitudes of waves with very short rise times (high frequencies) to produce the sharp attack of the cymbal. This insight from Fourier analysis can be generalized to say that any sound with a sharp attack, or a sharp pulse, or rapid changes in the waveform like a will have a lot of high frequency content.
The Fourier transform is used for the spectral analysis of time ..
Once you know the harmonic content of a sustained musical sound from Fourier analysis, you have the capability of synthesizing that sound from a series of pure tone generators by properly adjusting their amplitudes and phases and adding them together. This is called Fourier synthesis.
The Scientist and Engineer's Guide to ..
Abstract-A theory of short term spectral analysis, synthesis, and modification is presented with an attempt at pointing out certain practical and theoretical questions. The methods discussed here are useful in designing filter banks when the filter bank outputs are to be used for synthesis after multiplicative modifications are made to the spectrum. I N THIS paper, some practical and theoretical questions are considered concerning the analysis of and synthesis from a signal's short term spectrum. The short term spectrum, or time spectrum, are those signals which result from analyzing a single input signal with a set of filters which are selective over a range of frequencies [ l] -. In the case of analysis by a spectrum analyzer, the filters are either spaced contiguously or one filter is heterodyned over the frequency range of in-terest. For many applications, this is quite adequate. How-ever, when one is interested in both analysis and synthesis, a