DVD Speed Burn Graph


I wonder if anyone can help with telling me what the issue is with these dvd burns? The graphs are from a speed test with DVD InfoPro, and there seem to be drops in speed at relatively uniform distances throughout the entire disc. The first is with a DVD +R, and the second with a DVD +RW. Both are Verbatim, 16x and 4x max respectively.

I used a 6x burn speed on the DVD+R and 4x on the DVD+RW, but i’ve also tried higher burn speeds on this and other media and still get the bumps at regular intervals.

The discs all seem to work ok, but I would like to get smooth burns and want to know if this is a configuration, hardware or media issue.

Thanks in advance.

Edit: I don’t have DVD Info Pro sorry.