Im reviewing the documentation more calmly and is the first time i realize about some interesting details of the "smpl" chunk that worths to be mentioned, i guess you realized about it too but im going to make a recap
Please check the descriptions in this link while reading my post
https://sites.google.com/site/musicgapi/technical-documents/wav-file-format#smpl
As an introduction... the "smpl" chunk have a variable size, because is composed by 0x2C bytes + a "list of sample loops" composed by a variable number of loops. Every loop is 24 bytes (0x18), and the GWAT3 tool only adds 1 loop
0x00 4 Chunk ID <-------------------- static (0x736D706C)
0x04 4 Chunk Data Size <-------------------- static 36 + (1 * 24) + 0 = 60 (0x3C)
0x08 4 Manufacturer <-------------------- static GWAT3 uses 0, but you can use the 0x4C for
sony 
0x0C 4 Product <-------------------- static GWAT3 uses 0, not sure if there is an ID for the PSP and other for PS3
0x10 4 Sample Period <--------------------
i dont understand how to calculate this value
0x14 4 MIDI Unity Note <--------------------
0x3C again ?, it seems GWAT3 uses the same value here than in the "Chunk Data Size"
0x18 4 MIDI Pitch Fraction <-------------------- GWAT3 uses 0
0x1C 4 SMPTE Format <-------------------- GWAT3 uses 0 (the file doest seems to have SMPTE)
0x20 4 SMPTE Offset <-------------------- GWAT3 uses 0 (the file doest seems to have SMPTE)
0x24 4 Num Sample Loops <-------------------- static GWAT3 uses 1 (because there is only 1 loop inside the "list of sample loops"
0x28 4 Sampler Data <-------------------- static this is the total size of the "list of sample loops" (1 loop = 24 bytes = 0x18)
-------------
Now, inside the loop (24 bytes)
0x00 4 Cue Point ID <-------------------- static GWAT3 uses 0
0x04 4 Type <-------------------- static, GWAT3 uses 0 (Loop forward, normal)
0x08 4 Start <-------------------- static, GWAT3 uses 0.
This is what i was changing with a hexeditor !!!
0x0C 4 End <-------------------- the default GWAT3 loop is always aligned to the end of the audio track
0x10 4 Fraction <-------------------- static, GWAT3 uses 0
0x14 4 Play Count <-------------------- static, GWAT3 uses 0 (it means infinite loop)
Code:
Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
00000040 73 6D 70 6C 3C 00 00 00 00 00 00 00 smpl<.......
00000050 00 00 00 00 94 58 00 00 3C 00 00 00 00 00 00 00 ...."X..<.......
00000060 00 00 00 00 00 00 00 00 01 00 00 00 18 00 00 00 ................
00000070 00 00 00 00 00 00 00 00 00 58 0E 00 FF D7 1B 00 .........X..ÿ×.. <--- this is the loop (24 bytes)
00000080 00 00 00 00 00 00 00 00 ........
From that list there are only a couple of values i dont know how to calculate, but most of them are easy