A twisted pair cable consists of two insulated conductors twisted together. These cables can drive balanced lines. A balanced cable (see balanced signal) is a configuration of two electrically identical conductors. The electrical signal is referenced to ground that is point zero in the circuit. Balanced lines reject noise from low-frequency 50/60 Hz (Power line) up to megahertz or higher signals.
Virtually all professional audio installations use shielded twisted pair for audio signals because of its noise rejection. Microphone and Line level audio signals between -60 and -20 dBu and +4 dBu respectively, are transmitted over twisted pair.
In consumer equipment, line level is -10 dBV and the cable has a single “hot” conductor and a shield, which we call unbalanced cable. These cables are effective only for short distances and they only have the noise protection offered by the shield.
Initially, twisted pair wiring was designed to transmit low frequency signals, such as telephone audio signals. Later, twisted pair cables began to be designed to transmit high frequency signals, such as data signals (Category cables). As a result, USB, DVI, HDMI, IEEE 1394 cables, among others, also transmit their signals through twisted pair cables.
