Код:

@echo off
setlocal enableextensions enabledelayedexpansion
set sSourceFile=sound.mp3
set /a iCount = 1
if not exist "%sSourceFile%" (
echo Source file [%sSourceFile%] not found.
exit /b 1
)
:Repeat
for %%i in ("%sSourceFile%") do 2>nul ren "%sSourceFile%" "%%~ni!iCount!%%~xi" || (
set /a iCount += 1
goto :Repeat
)
endlocal
exit /b 0