The treble clef appears in high woodwinds, brass and vocal parts. An interesting characteristic of the treble clef is the curved loop that wraps around the G line. The treble clef loop always wraps around the second line in modern music; however, it is theoretically possible to move the position of the loop and change the names of the pitches in the treble clef. For this reason, the treble clef received the name the G clef since it indicates where G is above middle C.
The alto clef looks like a backwards bracket. The middle of the bracket falls on middle C. In a true alto clef, middle C appears on the middle line. If the bracket moves so that the middle of the bracket falls on any line other than the middle line, it is technically a C clef. There are several types of C clefs, including tenor, soprano, mezzo and a general C clef that may be positioned anywhere on the staff.
The word treble by itself may refer to several aspects of a composition or piece of music. It can refer to the highest pitched instruments or vocal part in a composition, the range of a child's voice or even the highest frequencies on your stereo equalizer. The one thing that the varying definitions of treble have in common is that it refers to something that is high-pitched. Sopranos and young boys voices often sing in the treble range.
The word alto itself may refer to an alto voice in a choir. It may also refer to the range that a particular instrument plays in relation to other instruments of the same family. For instance, the viola often gains the distinction of the alto of the string family since it plays in the middle to upper middle part of the range. Most commonly, alto will refer to a singer whom has a range of approximately A below middle C to the E on the top space of the treble clef.