Phantom power, in the context of professional audio equipment, is DC electric power transmitted through microphone cables to operate microphones that contain active electronic circuitry. It is best known as a convenient power source for condenser microphones, though many active direct boxes also use it. The technique is also used in other applications where power supply and signal communication take place over the same wires. Phantom power supplies are often built into mixing consoles, microphone preamplifiers and similar equipment. In addition to powering the circuitry of a microphone, traditional condenser microphones also use phantom power for polarizing the microphone's transducer element. History Phantom powering was first used (and still is used) in copper wire based landline telephone systems since the introduction of the rotary-dial telephone in 1919. One such application in the telephone system was to provide a DC signaling path around transformer-connected amplifiers such as analogue line transmission systems. The first known commercially available phantom-powered microphone was the Schoeps model CMT 20, which came out in 1964, built to the specifications of French radio with 9–12 volt DC phantom power; the positive pole of this powering was grounded. Microphone preamplifiers of the Nagra IV-series tape recorders offered this type of powering as an option for many years and Schoeps continued to support "negative phantom" until the CMT series was discontinued in the mid-1970s, but it is obsolete now. In 1966, Neumann GmbH presented a new type of transistorized microphone to the Norwegian Broadcasting Corporation, NRK. Norwegian Radio had requested phantom-powered operation. Since NRK already had 48-volt power available in their studios for their emergency lighting systems, this voltage was used for powering the new microphones (model KM 84), and is the origin of 48-volt phantom power. This arrangement was later standardized in DIN 45596. Standards The International Electrotechnical Commission Standards Committee's "Multimedia systems – Guide to the recommended characteristics of analogue interfaces to achieve interoperability" (IEC 61938:2018) specifies parameters for microphone phantom power delivery. Three variants are defined by the document: P12, P24 and P48. In addition, two additional variants (P12L and SP48) are mentioned for specialized applications. Most microphones now use the P48 standard (maximum available power is 240 mW). Although 12 and 48-volt systems are still in use, the standard recommends 24-volt supply for new systems. Technical information Phantom powering consists of a phantom circuit where direct current is applied equally through the two signal lines of