A ringing signal is an electric telephony signal that causes a telephone to alert the user to an incoming call.
Apple says there Ring Tones are extended than half a million songs on iTunes that can be devoted as ringtones, but when you browse the whole library there's no guarantee that your favorite song will be available. Frequently, an original artist's version is not available, but a karaoke version is. As terrible as that sounds, it can work. Think of it as a customized Garage Band bop loop. I wouldn't listen to it on my iPod but it works as a ringtone.