Hello here I will explain how to edit ped voices in Grand Theft Auto IV.
First, you will need flitskikker's IV Audio Toolbox which can be downloaded @ http://gtaforums.com/topic/536856-ivrelalpha-iv-audio-toolbox/
Install it, and then also download the source and extract it to where you installed IV Audio ToolBox.
Also, you will need a recording program. I recommend Audacity which is free and can be downloaded @ http://audacity.sourceforge.net/download/
Use OpenIV (if you don't have it, http://openiv.com/WebIV/guest.php?get=1 ) to open Speech.rpf and then look for the ped you'd like to edit and extract it to where ever you want. I usually make a new folder on desktop for quick access.
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Run IVAudioToolBox.exe and open the IVAUD file that you want to edit. When you open a file, it will ask for File Type, Single Channel or Single Channel Compressed. Go with the one that the program guessed.
In IV Audio ToolBox, you will see this:
Size and Offset don't really matter. What matters is Sample Rate, Duration, and Channel. The recording's or files you have, have got to be single channel (mono). Sample Rate has to be exact or could crash your game. Also, the duration must be either smaller or about the same. If you're a couple seconds longer, for example, a file you want to replace is 0:03 and the new file you have is 0:05, you should be good. Just don't do it a lot because you're game will crash. I experienced this when I edited the m_zombie bank and had a few sound files over 5 seconds and within 15 seconds the game crashed back to desktop.
Select the audio you want to replace and then press the replace button:
Choose the audio file where ever you placed it and either press Open or double-click and the next menu that pop's up should look like this or similar:
Now hit replace and it should do the trick. Do this to as many as files you want and then Save over the original. Go back to OpenIV, go to Resident, and replace the old IVAUD with your new edited one and then press rebuild.
If you're using Audacity this is just a little more info on how to Resample, change the audio to single channel and how to get the megaphone voice effect.
Correcting the Sample Rate:
Changing to Single Channel:
Select 'Split Stereo to Mono'
At the top of the menu bar where it says Effect, go down to Equalization... and then adjust the the sliders like this:
Press OK and you're done. You can also adjust these sliders to your own liking. Now it's time to export! Go to File > Export... Then name your file whatever you want and then choose Save as Type:
Press save and ignore the next menu that comes up and just press OK. And that's it you're done. This is my first tutorial, hope you guys find it useful. Also if you have anything else to add, feel free.
Here is example my editing of m_y_heli_cop bank. Enjoy