sinatra-app.rb

require 'rubygems'
require 'sinatra'
require 'tempfile'

get '/audio' do

  text = params['text']
  temp_file = Tempfile.new 'mp3'

  # generate mp3 to temp file
  system("echo \"#{text.to_s}\" | text2wave | /opt/local/bin/lame - - > #{temp_file.path}")

  # output it
  headers 'Content-Type' => 'audio/mp3'
  send_file temp_file.path

end