The following demonstrates how to modify the settings for the preferred format "Ogg Vorbis":

Create a GstVorbisEnc.prs preset file:

$ sudo gedit /usr/share/gstreamer-0.10/presets/GstVorbisEnc.prs

[_presets_]

element-name=GstVorbisEnc

version=0.10.36



[Default]

name=vorbisenc

bitrate=-1

quality=0.6

managed=false

The [Default] section contains the settings for the "Default" preset. The example I have given above is for 0.6 quality (~192kbps) VBR encoding. The default is 0.3 (~112kbps). Quality can be set from -0.1 to 1.0. There is further information on these settings at http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-base-plugins/html/gst-plugins-base-plugins-vorbisenc.html

Now add the line "preset = Default" to the [streamprofile-oggvorbis-1] section in rhythmbox.gep:

$ sudo gedit /usr/share/rhythmbox/rhythmbox.gep

...

[streamprofile-oggvorbis-1]

parent = oggvorbis

type = audio

format = audio/x-vorbis

presence = 1

preset = Default

...

And this demonstrates how to modify the settings for the preferred format "MPEG Layer 3 Audio":

Create a GstLameMP3Enc.prs preset file:

$ sudo gedit /usr/share/gstreamer-0.10/presets/GstLameMP3Enc.prs

[_presets_]

element-name=GstLameMP3Enc

version=0.10.36



[Default]

name=lamemp3enc

target=bitrate

bitrate=128

cbr=true

encoding-engine-quality=high

mono=false

The [Default] section contains the settings for the "high" preset. The settings above are for 128kbps stereo CBR encoding. There is further information about the possible values at http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-ugly-plugins/html/gst-plugins-ugly-plugins-lamemp3enc.html

Add the line "preset = Default" to the [streamprofile-mp3-1] section in rhythmbox.gep:

$ sudo edit /usr/share/rhythmbox/rhythmbox.gep

...

[streamprofile-mp3-1]

parent = mp3

type = audio

format = audio/mpeg, mpegversion=1, layer=3

presence = 1

preset = Default

...

Thanks to preiaen for providing the link that helped me find a solution:

Bug #945987 “No Settings are available in “Preferred format”
https://bugs.launchpad.net/ubuntu/+source/rhythmbox/+bug/945987

This led to the following pages where I found further information:

[SOLVED] How to edit CDRip settings in Rhythmbox - Ubuntu Forums
http://ubuntuforums.org/showthread.php?t=1965432

Linux Format forums :: View topic - Ubuntu 12.04 LTS Released
http://www.linuxformat.com/forums/viewtopic.php?p=106176