Because all default Duke3D sounds' files are defined as *.VOC in the CON files. EDuke32 will use whatever files are laying in the root folder with the
same exact name, this means even the file type. If it's defined as a .VOC it won't recognize a .WAV or .OGG in it's place, unless you change the con files to reflect that.
USER.CON even gives you a basic run down on adding sounds.
This is an updated version of USER.CON's rundown by
me Hendricks266. It includes new information relevant to EDuke32.
// MAXIMUM NUMBER OF SOUNDS: 2560 ( 0-2559 )
/*=-----------------------------------------------------------------------------
ABOUT CHANGING SOUND EFFECTS
The sound effects section follows this explanation.
The program expects to find any sound file that is in one of the following formats:
.VOC - Creative Voice
.WAV - 8-bit unsigned mono wave
.OGG - OGG Vorbis
The numbers that are to the right of the sound file name are technical parameters.
#1 - The first 2 numbers define a random pitch variation range.
#2 They can be positive or negative numbers.
#3 - The 3rd number is a priority flag.
#4 - The 4th number is a technical bitfield. See below.
#5 - The 5th number is a volume adjustment. It can be positive or negative.
=-------------------------------------------------------------------------------=
SOUND DEFINITION BITFIELD
Add the numbers in (parentheses) to calculate your sound's bitfield value.
Bit #0 (1) The sound repeats if continually played.
Bit #1 (2) The sound is an ambient effect. Disabling ambience will mute this sound.
Bit #2 (4) The sound is a player voice. Disabling "Duke Talk" will mute this sound.
Bit #3 (8) The sound contains offensive content. Disabling "Adult Mode"/enabling parental lock will mute this sound.
Bit #4 (16) The sound will always be heard from anywhere in the level. (sndist = 0)
Bit #7 (128) The sound is used in Duke-Tag.
---------------------------------------------------------------------------=*/
An example sound definition looks like this;
In USER.CON:
definesound PRED_ROAM roam06.voc 0 0 3 0 0
In DEFS.CON:
define PRED_ROAM 110
------------------
I suggest you read
the manual to get up to speed on things before you ask questions. It's not complete but it covers all the basic stuff.