GPL 3.0 license compatibility with this custom license

Question

I want to use paulscode sound system (http://www.paulscode.com/forum/index.php?topic=4.0) in GPL-3.0 licensed open source project.

The library has the following license (it seems it is custom written license):

The SoundSystem License:

You are free to use this library for any purpose, commercial or otherwise.
You may modify this library or source code, and distribute it any way you
like, provided the following conditions are met:

1) You may not falsely claim to be the author of this library or any
   unmodified portion of it.
2) You may not copyright this library or a modified version of it and then
   sue me for copyright infringement.
3) If you modify the source code, you must clearly document the changes
   made before redistributing the modified source code, so other users know
   it is not the original code.
4) You are not required to give me credit for this library in any derived
   work, but if you do, you must also mention my website:
   http://www.paulscode.com
5) I the author will not be responsible for any damages (physical,
   financial, or otherwise) caused by the use if this library or any part
   of it.
6) I the author do not guarantee, warrant, or make any representations,
   either expressed or implied, regarding the use of this library or any
   part of it.

Author: Paul Lamb
http://www.paulscode.com

Is such a license compatible with a license like GPL-3.0 or are there any parts making it incompatible.

With compatibility, I mean dynamically linking to the JAR of the library for the use in GPL-3.0 licensed project.

There is also JOGG plugin part of the library, with only this written for the license:

J-Ogg License:

You are free to use, modify, resdistribute or include this software in your
own free or commercial software. The only restriction is, that you make it
obvious that your software is based on J-Ogg by including this notice in the
documentation, about box or whereever you feel apropriate:

"This software is based on or using the J-Ogg library available from
http://www.j-ogg.de and copyrighted by Tor-Einar Jarnbjo."

How is the compatibility with this license?

Are there any tips on what to look for when dealing with "custom open source" licenses in sense of GPL-3.0 compatibility?

Answer 1

A license is GPL-compatible if it allows you to do everything that the GPL allows you to do, and if the license doesn't impose requirements or conditions other than those which the GPL also has or allows.

Both of the licenses you've shown are permissive licenses and seem open source, similar to the MIT or BSD licenses. They seem to provide you with the necessary rights. Where the licenses impose extra conditions (such as the J-OGG license requirement to provide a certain attribution notice), this seems compatible with the GPLv3 section 7 “additional terms” mechanism.