module ActionView::Helpers::AssetUrlHelper

audio_url "horse.wav", host: "http://stage.example.com" # => http://stage.example.com/audios/horse.wav

options is set, it overwrites global +config.action_controller.asset_host+ setting.
Since +audio_url+ is based on +asset_url+ method you can set +:host+ options. If +:host+
This will use +audio_path+ internally, so most of their behaviors will be the same.
Computes the full URL to an audio asset in the public audios directory.

def audio_url(source, options = {})
  url_to_asset(source, { type: :audio }.merge!(options))
end