YouTube to mp4 stereo

ok, so I learned if you add the text as follows:
&fmt=18

to a YouTube url, you can get better quality pic and sound (stereo on many). I use videodownload.com and youconvertit type websites to download to a .flv, and then use 3gp converter to convert to mp4 for the video ipod. My question is why I do not retain the awesome stereo sound after conversion that I am hearing when playing online with YouTube? Is there a better process? Thanks for any thoughts. Mark

 

I have a theory, wonder if any concur. The added text provides a simulated stereo while online that does not transfer to a download?