Example waveform generator

Verify that the time step provides an appropriate resolution. The time step must be small enough to provide appropriate resolution of the switching waveforms generated by the simulation. The time step should be assigned to an order of magnitude smaller than the shortest period in the simulation. For example, in a 100 kHz oscillator, the period is 10 /is. The time step should be set to 1 /is. 

Consider, for example, a test sample of material with a well-defined geometry as shown in Fig. 2. Reversible electrodes are attached to opposite planar faces of the test article, and a sinusoidal electrical potential (V ) is applied via a waveform generator. The current response is monitored with a frequency response analyzer (FRA), which converts the signal to the frequency domain. The amplitude (A) of the input wave is adjusted to the range in which the system responds linearly, about 10 mV. Thus, the perturbation can be described by the following equation ... 

Several real-life examples have also been used for Amical evaluation. The most complex is a programmable waveform generator. The design is composed of four modules. The largest module results in an FSM with 548 states and 1,474 transitions. The compilation of this block takes less than one minute on a Sun SPARCstation 2. 

Examples of the waveforms generated by a highly damped structure and an undamped structure are given in Figure 8.4. 

As discussed above, the operation of ion traps is frequently described using scan functions. Rgure 9.4 shows the RF scan function used to generate a full-scan MS and includes example waveforms from other dynamic devices (see Figure 9.11a). Several additional features of... 

Modification is performed by separating the harmonics from the spectral envelope, but this is achieved in a way that doesn t perform explicit source/filter separation as with LP analysis. The spectral envelope can be found by a number of numerical techniques. For example, Kain [244] transforms the spectra into a power spectrum and then uses an inverse Fourier transform to find the time domain autocorrelation function. LP analysis is performed on this to give an allpole representation of the spectral envelope. This has a number of advantages over standard LP analysis in that the power spectrum can be weighted so as to emphasise the perceptually important parts of the spectrum. Other techniques use peak picking in the spectrum to determine the spectral envelope. Once the envelope has been found, the harmonics can be moved in the frequency domain and new amplitudes found from the envelope. From this, the standard synthesis algorithm can be used to generate waveforms. 

The differences among the second-generation techniques mainly arise from how explicitly they use a parameterisation of the signal. All use a data-driven approach, but some use an explicit speech model (for example using LP coefficients to model the vocal tract) whereas others perform little or no modelling at all, and just use raw waveforms as the data. 

The output of the HMM synthesis process is a sequence of cepstral vectors and FO values, and so the final task is to convert these into a speech waveform. This can be accomplished in a number of ways, see for example Section 14.6. In general though the approach is to use the generated cepstral output to create a spectral envelope, and use the generated FO output to create an impulse train. The impulses are then fed into a filter with the coefficients derived from the cepstral parameters. While reasonably effective, this vocoder style approach is essentially the same as that used in first generation systems and so can suffer from the buzz or metallic sound characteristic of those systems (see Section 13.3.5). A major focus of current research is to improve on this. 

A particularly Important example of this Interactive capability occurs in the analysis of time-of-flight diffraction inspection data files. Following display of the set of ultrasonic rf waveforms stored in each file on the colour graphics unit, a screen cursor is used to select points on identified waveforms for display as time-delay ellipses on the appropriate nozzle profile. The intersection point of the arcs generated from the same point on several waveforms corresponds to the location of the defect extremity producing the observed signal. 

In practice, simple observation of the bir tential waveform is often veiy useful. For example, a common bicqiotential receding is the fetal ECG. Electrodes are placed on the mother s abdomen to bring the bioelectric monitoring point close to the source howevo, the fetal current generators are still relatively weak. Furthermore, the mother s ECG is also captured in the recording. Nonetheless, the two waveforms are easily discriminated by a trained eye. The fetal ECG is typically faster. 

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