Setting mp3 quality when using rhythmbox to sync iphone or ipod

When I sync music library with iphone in ubuntu, rhythmbox convert almost any type of music file into mp3 file automatically.

However, the default quality set is vbr, and I want the best quality, i.e., 320kbps, not vbr.

Rhythmbox - Edit - Preference - Music - Edit Preferred format
Select MP3.

Change the setting like this :

audio/x-raw-int,rate=44100,channels=2 ! lame name=enc mode=0 vbr=0 bitrate=320 ! id3v2mux

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