Rendered mp3 file is much larger than original In Sony Vegas Pro 10 I've placed an .mp3 file (about 3MB file size), then I've cut it slightly at the end to shorten the length. I've tried to encode it with following settings:

File - Render As  
Save As Type: MP3 Audio  
Template: Default Template  
Description: Audio: 256 Kbps, 44,100 Hz, 16 Bit, Stereo, MP3


The encoded file is about 6MB and it seems that the resulting file is the same quality as original.

How can I render .mp3 without getting a larger file size than the original?
The settings say Stereo. The doubling of file size might indicate that the original file was mono.