On Sun, Dec 12, 2004 at 06:54:46AM +0300, Andrew Gaydenko wrote: > 1. Can anybody explain me (I think, Fons Adriaensen can :-) the > JAAA "Bandw" parameter meaning? The bandwidth determines how much detail you see on the frequency scale. If you have a small bandwidth, you will be able to separate two signals that are very close together in frequency, while for a larger bandwidth they will merge into a single peak. So why not use a very small bandwidth all the time ? The reason is that small bandwidth requires a longer FFT, and you will see less detail in time. So there is a tradeoff to be made between resolution in time and in frequency.
> 2. When Bandw parameter is rather small, I see two spectrums - main (blue) > and, below the first, - the second one (gray). What is the last spectre > spectrum > meaning? >From the README : 'Bandw' sets the FFT length, and hence the bandwidth of the analyser. Depending on this value, the size of the display and the frequency range, you may sometimes see two traces. This happens when the resolution of the analyser is better than the display, so that one pixel contains more than one analyser value. In that case, the blue trace is the peak value over the frequency range represented by each pixel, and the gray one is the average value. The first one is correct for discrete frequencies, and the latter should be used to read noise densities. To see this, switch on both the sine and noise generators, and loop back into JAAA. Set a bandwidth and frequency range that gives you the two separate traces. Now put a peak marker on the tone, and a noise marker somewhere on the noise. You will see that the noise marker is on the gray trace. -- FA
