<P> The direct box takes a high impedance, unbalanced signal and converts it to a low impedance, balanced signal . This allows the signal to be sent over long cable runs with significantly less signal loss (especially in high frequencies) due to the lowering of the impedance, and greater rejection of interference due to the benefit of common mode rejection in a balanced signal . Furthermore, the lower impedance (around 600 ohms is normal) allows an insignificant load to the input of a mixing console or preamp which is also designed to accept input from low impedance microphones . </P> <P> Because all cables used in live sound and recording are "capacitive", long cables used without a DI box can become a "low ‐ pass filter" which reduces the high end frequencies . Using a DI box provides a balanced cable, which reduces radio frequency noise and electromagnetic problems coming from lighting systems . Mic cables are typically balanced XLR cables; on the other hand, the output from an electric bass or electric guitar is usually a 1 / 4" unbalanced cable . Another advantage of DI units is that the DI contains a "...balancing transformer" that reduces "ground ‐ loop problems and potential electrical safety issues under fault conditions". </P> <P> A passive DI unit typically consists of an audio transformer used as a balun . The term "passive" indicates that the unit does not require a battery or other power source to operate . This makes passive DIs less expensive, but it also means that they cannot include preamplifier features which enable the user to boost the gain . The turns ratio on a passive DI is typically chosen to convert a nominal 50 kΩ signal source (such as the magnetic pickup of an electric guitar or electric bass) to the 100--200 Ω expected by the mic input of an audio mixer . Typical turns ratios are in the range of 10: 1 to 20: 1 . Less commonly, a passive DI unit may consist of a resistive load, with or without capacitor coupling . Such units are best suited to outputs designed for headphones or loudspeakers . </P> <P> The less expensive passive DI units are more susceptible to hum, and passive units tend to be less versatile than active . However, they require no batteries, are simpler to use, and the better units are extremely reliable when used as designed . The lack of batteries in passive DIs means that users do not have to worry about batteries losing their power in the middle of a live show or recording session . </P>

What is a di output on an amp