I can't see the signals!

If the signal window is solid white or light grey, and your version of WAVE is older than 6.8, your X server does not have backing store enabled. Click on any of the navigation controls (e.g., \ovalbox{\rule[-.3mm]{0cm}{2.5mm}\small\sf ~\tt <<~}, \ovalbox{\rule[-.3mm]{0cm}{2.5mm}\small\sf ~\tt <~}, \ovalbox{\rule[-.3mm]{0cm}{2.5mm}\small\sf ~\tt >~}, or \ovalbox{\rule[-.3mm]{0cm}{2.5mm}\small\sf ~\tt >>~}), or resize the window, to make the signals appear. If this works, the problem is almost certainly that backing store has been disabled in the X server's configuration file. You can verify this by running the command

	xdpyinfo | grep backing
To enable backing store, insert the line
	Option "backingstore"
in the Device section of your X server's configuration file (usually /etc/X11/xorg.conf or /etc/X11/XF86Config), or run the server with the option ``+bs'' to obtain the same result. See the documentation for your X server for further information.

If the signal window is solid or nearly solid blue (or black if you have a monochrome or greyscale display), the signals are too big. WAVE may be attempting to display signals that fill the entire window. In rare cases, noise in the signals themselves can produce this effect. More common causes include incorrect signal format or gain specifications in the header file for the record you have opened, incorrect display calibration, or a choice of amplitude scale that results in excessive vertical range of one or more signals. This effect can also occur as a result of various problems related to the WFDB calibration file, for example, if the WFDBCAL environment variable does not name an accessible WFDB calibration file (see wfdbcal(5) for details), if any of the signals in the record are of types not listed in the WFDB calibration file, or if the WFDB calibration file does not contain appropriate default display scales for all of the signal types in the record. See the next several questions for suggestions on correcting these problems.

If the signal window contains horizontal lines (in blue if you have a color display) where the signals should appear, the signals are too small. In this case, the signal gains specified in the header file may be incorrect, the display calibration may be incorrect, or you may have specified an amplitude scale that reduces the vertical range of the signals to zero. Click on \ovalbox{\rule[-.3mm]{0cm}{2.5mm}\small\sf ~View...~} to check the scales, and adjust them if necessary.

If the signal window contains time indicators in the lower corners, look for the signal names along the left edge of the window. If there are no signal names visible, click on \ovalbox{\rule[-.3mm]{0cm}{2.5mm}\small\sf ~View...~}, then on signal names and \ovalbox{\rule[-.3mm]{0cm}{2.5mm}\small\sf ~Redraw~} in the View window. If signal names still do not appear, either the header file or the signal file for the record you have opened may be inaccessible. Find these files (see ``File-related questions''), add the directory that contains them to your WFDB path, and try to read a few samples using `rdsamp -r record -t 1'. If this fails, examine the header file for the record (a text file), and be sure that it specifies at least one signal in an accessible signal file.

George B. Moody (george@mit.edu)