First install ASI loader; you can download it here:
http://www.gtagarage.com/mods/show.php?id=8321

weaponsound.txt is the sound configuration for all weapons. With weaponsound.txt, you can change the pitch and sound ID of each weapon sound.

To edit, line up weaponsound.txt with weapons.txt in Notepad to match the weapon name to its sound configuration line.

Here are the important values in weaponsound.txt:

a = Weapon sound category
	
	0: No gun sound
	1: Normal gun sound
	2: Start+Loop sound (ex. flamethrower)
	3: Continous loop (ex. fire extinguisher)
	4: Camera
	5: Minigun loop (not configurable)
	6: Goggles
	
b = Pitch of far shot/reverberation sound (1 = normal / plays reveration sound as it is)
c = Pitch of initial shot sound (1 = normal / plays sound as it is)
e = Sound ID of far shot/reverberation sound

	2: SMGs (sound_003) ***
	5: Assault rifles (sound_006)
	8: Pistols (sound_009)
	23: Shotguns / full power rifles (sound_024)

	*** Note that for this mod, submachine guns actually use the pistol far shot/reverberation sound (since they're the same type of caliber), while the sound previously used for SMGs is now the reverberation sound for the suppressed pistol (since it didn't have one before).

f = Sound ID of initial shot sound

	1: Machine pistols (sound_001, sound_002) ***
	4: Assault rifles (sound_004, sound_005)
	7: Pistol / Desert Eagle (sound_007, sound_008) ***
	18: MP5 (sound_018, sound_019)
	22: Shotguns (sound_022, sound_023)
	24: Suppressed pistol (sound_025, sound_026)
	27: Full power rifles (sound_027, sound_028)

	*** Note that for this mod, the sound normally used for the MAC-10 and TEC-9 is now used for the 9mm pistol, allowing for the Desert Eagle to have its own sound.


I'm not sure what the values of d, g, h, and i change.


Most of the gun sounds are located within this block in the middle of the file:

	
a	b	c	d	e	f	g	h	i	

1	1.07	1.07	0.0	8	1	6	35	34 //Pistol
1	1.0	1.0	-7.0	2	24	24	77	76 //Suppressed Pistol
1	0.80	0.91	0.0	8	7	6	35	34 //Desert Eagle
1	0.95	0.95	0.0	23	22	21	74	73 //Shotgun
1	1.03	1.03	0.0	23	22	21	74	73 //Sawn-off shotgun
1	0.93	0.93	0.0	23	22	21	74	73 //SPAS-12
1	1.03	1.03	0.0	8	1	6	30	29 //Micro-Uzi/MAC-10
1	1.00	1.00	0.0	8	18	6	30	29 //SMG (MP5)
1	0.93	0.93	0.0	5	4	3	53	33 //AK-47
1	1.00	1.00	0.0	5	4	3	53	33 //M4
1	1.06	1.06	0.0	8	1	6	30	29 //Tec-9
1	0.95	0.95	0.0	23	27	26	53	52 //Country Rifle
1	0.8	0.8	0.0	23	27	26	53	52 //Sniper Rifle
