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Q. How do I update my product license?
A: When you run AutoSignal, go to the help menu and select "Update Product License." Enter your new license code. Hit the "Update License Code" button.
Q. Why does my system slow down when I run Short-Time Fourier Transforms and Continuos Wavelet Transforms? What can I do to improve performance?
A: The Short-Time Fourier Transform and Continuous Wavelet Transform options are particularly memory intensive. For the STFT, a separate FFT is generated for each segment. Similarly, separate FFTs are made for each scale or frequency in the CWT. For memory reasons, AutoSignal limits the number of STFT segments (time snapshots) to a maximum that will be in the vicinity of 512 and the number of evaluated CWT frequencies is limited to a maximum of 100.
The STFT is especially prone to using up available memory. In the CWT, zero padding is only used to prevent wraparound effects in the convolution. No additional memory is used as a consequence of zero padding. In the STFT, however, zero padding results in additional spectral frequencies whose magnitudes must be stored in memory. In both cases, the spectral data is fitted to a bicubic B-spline for 3D rendering and surface integration. AutoSignal limits the total rendering grid to 16,384 elements. If the spectral grid is larger than this, an averaging decimation is used. An STFT or CWT surface is then stored as a grid of B-spline coefficients that consumes yet more memory.
The amount of physical memory (RAM) free for AutoSignal's use is shown in the main status window in the Mem field. When dealing with large data sets, particularly WAV files, it is not difficult to exhaust this memory. When this happens, Windows uses the hard disk for memory operations. Excessive disk activity and extremely slow processing and procedure closure times will result if the physical memory is insufficient.
To best conserve memory resources with the STFT, zero pad the segments only when absolutely necessary, and do so only to the extent this is needed for frequency resolution. Further, avoid high overlap settings which result in such a large number of segments. The relation with overlap is not linear. A modest increase in overlap may significantly increase the number of segments and the amount of memory required. Although AutoSignal permits overlaps as high as 90%, there is usually little benefit beyond 50-70%.
For the CWT, the 35 frequency default is usually adequate. When very low frequencies are present, 35 logarithmic frequencies generally suffice. When both very low and high frequencies are present, a higher frequency count may be required. In the CWT, the memory relationship is linear. Doubling the frequency count doubles the amount of physical memory needed. Typically, there is little to gain beyond 50-60 CWT frequencies.
If these guidelines are insufficient to prevent the hard disk thrashing and drastically diminished performance that results from exhausting physical memory, you can try breaking up the large data stream into smaller separate data sets. Given the relatively low cost of RAM, upgrading to 64, 96, or 128 Mb may be a good investment if you will be doing a good deal of non-stationary analysis of large data streams.
Q. How can I make sure I have the appropriate signal space for multicomponent radioactive decay data?
A: The Prony Spectrum procedure is useful for fitting waveforms consisting of damped sinusoids as well as fitting data that consist of multiple simultaneous first order exponential decays. Since a damped sinusoid requires two eigenmodes of signal space to be represented, and an exponential decay requires only a single eigenmode, AutoSignal seeks to automatically set the component count in the Prony procedure based upon the type of signal elements present. If a component's frequency is less than 1e-8*Nyquist, it is treated as a real exponential. If the Allow Real Exp option is checked, the component is assigned one eigenmode of signal space. Otherwise, the component is not included in the Prony fit. If a component's frequency is non-zero, it is assumed to be a damped or undamped sinusoid, and two eigenmodes of signal space are assigned.
When modeling continuously decreasing multicomponent radioactive decay data, use one unit of signal space for each component present. For three different components that have appreciably different half-lives, the signal space should be set to 3 rather than 6.
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