What is a packet audio converter for Ubuntu Linux with some features?

Question

linux

Dear community, please help me find a program (or script) for solving one, at first glance, simple task - batch converting audio files (specifically mp3).
There are some requirements for this program:
- Preferably with a GUI (but not critical);
- Ability to process a large number of files, here I would like multithreading (again, not critical);
- Work on Linux OS, preferably on the latest version of Ubuntu;
- And the most important thing is the ability to skip files whose bitrate is lower than that set by me, or the one to which the conversion is taking place.
A number of mp3 files with music have accumulated, some from a long-standing music collection, the other was simply downloaded as mp3 files directly from Pavel Durov's former site. Selected a number of songs to listen to in the car, some part to listen to using the phone.
The problem is that about half of these files have a bitrate of 320 kbps and, accordingly, take up a lot of space on memory cards. I would like to recode files with a high bitrate, but not touch files with a small one, so as not to lose the already low sound quality.

Answer 1

# apt-cache search sox | grep ^sox
sox - universal sound processing tool

Answer 2

ffmpeg+parallel?

Answer 3

Apparently something like this is needed:

for file in *.mp3
do
    if 
    then
         sox "$file" -C 128.2 "$file.128k.mp3"
    fi
done