Contant Peak, Constant RMS, How to get a fixed value for peak and RMS Options

[terataz]

Hi, we are trying to set a default standard for the volume of the audio files we are working on.
We are looking for a tool that, given a bunch of mp3 files, will be able to normalize them at a given db.

For example : 0db for Peak levels and -9db for RMS.

Ideally, we'd love to use sox as we can chain it with other effects we're using without the need to convert multiple time the file from mp3 to wav and back.

We tried sox gain -n , sox gain -ne, sox gain -nb, sox loudness but none of them keep a constant RMS without varying the Peak level as well.
Any help appreciated.
Thanks

[splice]

Assuming that you want the files to be reproduced at what a listener would perceive to be a "standard volume", I suggest you implement "ReplayGain". This adds a tag to the MP3 file which causes any ReplayGain-aware MP3 decoder to adjust the perceived volume on playback to a set level. For non-aware decoders, there is a tool (MP3Gain) which goes through an MP3 file and adjusts the gain on each frame to match the ReplayGain value.