"The results of some of these Spanish bond issues would have been impossible just three months ago, but it's unclear to me whether what has now opened is really a long-term window," said Michael Gierse, a fund manager at Union Investment in Frankfurt, which has €180 billion in assets under management.
The long-term window size serves as the baseline for DC estimation.
It adopts the average spectrum over a long-term window instead of instantaneous values of the spectrum.
Thus, the long-term window should be minimally longer than the target base width to avoid suppressing it [2].
It is assumed that the presence of clutter will cause a monotonic rise or fall pattern in the values of the pixel's temporal profile at least during the duration of the long-term window.
Furthermore, depending on the choice of the long-term window length (R and M combination), the LSFM-based VAD applisation is expected to suffer a delay equal to the duration of the window (R + M − 1 frames).
The number of samples for each long-term window is denoted by M. The following linear model is used for estimating the DC; for the sake of simplicity, the description of the estimation is applied to a single window: (6).
where n is the noise, a and b are the coefficients that must be estimated, M is the number of samples for each long-term window, and y is the DC signal.
First, the distributions of the LSFM feature as a function of the long-term window length (R = 2, 5, 10, 20, 30, and 40) for white noise at five SNR levels (−10, −5,0, 5, and 10 dB) were studied.
Thus, the long-term window should be long enough to facilitate accurate estimation of background, on the one hand, and short enough to enable the influence of clutter to be tracked, on the other hand.
In Fig. 2, it is not difficult to find out that the distributions of speech and non-speech are more easily separated along with the increasing window length M. In corroboration, the speech classification error is reduced when increasing the order of the long-term window, as shown in Fig. 4.
