This library is called cut_audio. It uses ffmpeg to cut audio files in a convenient way. Version 1.0.3 added 'open' functionality so that we can edit the .rb file in question directly. Also, providing an end position is optional. If omitted we will default to the max length of the file in question.
Gemfile gem 'cut_audio', '~> 1.0.19'
install gem install cut_audio