Low impedance microphones are the most commonly used mics in the industry. They connect to a balanced line at the mixing console, and take advantage of common-mode rejection at the op-amp input IC. Being low impedance, the is little limitation on the length of the mic cable used. Low Z mics use XLR connectors exclusively. High Z mics use a ¼" phone plug, and long runs of mic cable will cause significant line loss and signal attenuation.

As with most audio products, money buys tone. Microphones vary greatly in tone, with the more expensive mics being the most linear and giving the best reproduction. Some mics are best used for vocals, others best for micing a guitar amp or drums. The most popular vocal mic has been, for many years, the Shure SM58, and the SM57 for miking instruments. The SM58 has a ball-type “pop” filter to reduce breath-noise in the mic. The SM57s do not, though you will see them occasionally used for a vocal mic.

Karaoke mics have controls to allow changing the pitch of the cover music, but are otherwise a standard vocal mic.

Cardioid mics are considered unidirectional in that they pick up with much greater gain from one direction, that being on-axis with the mic. They have a pick up or “polar” pattern shaped roughly like a heart (hence the term “cardioid”) with the narrow end toward the source of sound. This shape indicates that sound sources that are “off-axis” are rejected or at least reproduced at a lower level than sounds coming straight away from the mic. This is a definite advantage for the live performer as stage volumes can become quite high with drummers and guitarists playing in a confined area. If the mic picks up off-axis stage noise, it can limit the gain applied to the mic and can also cause feedback problems further limiting the mic. Cardioids require that the user speak or sing directly into the mic from a very close distance.

Omni-directional mics pick up equally well from all around, and would normally be used to mic a group of singers, such as a choir. This type of mic has greater bass response, and is therefore not suited for use like a cardioid. This type of mic would sound very “boomy” or have too much bass response if the user spoke or sang directly into it like a cardioid.

Condenser or electret microphones are much less common than Dynamic mics. These use a capacitive-type pickup (hence the term “condenser”) and requires a power supply to place a voltage across the pick up. As you know, the voltage across a capacitor is a function of the distance between the plates. The impinging audio signal strikes one “plate” alternately reducing and increasing the distance between the plates. This action modulates the voltage across the pick up. Most condenser mics today are inexpensive mics for tape recorders, etc., or very expensive studio mics than require phantom power from the mixing console to operate.