Just as important as the type of connector used is the wiring scheme used. Notice in the photo above that the XLR connectors have three connection points (either pins or sockets). Professional microphones with XLR connectors use an industry-standard “balanced” wiring scheme, with two of the pins used to carry audio and the third as a ground connection. There is no standard for the wiring of the 3.5 mm miniplug connectors used on sound cards, so the actual wiring scheme varies depending on the manufacturer of the card.

The 3.5 mm miniplug is commonly available in two different configurations. Most sound cards use a three-segment version, often called a “stereo” connector since it can be used to carry two separate channels of audio in addition to providing a ground connection.

When used as a microphone connector, the end portion of the connector (called the Tip) usually carries the audio signal; the center portion (called the Ring) is sometimes used to carry low-voltage dc power required by the microphone supplied with most computers; and the third section (called the Sleeve) is used as the ground connection. On the two-segment or “mono” version, the Sleeve is used for ground and the Tip of the connector carries the audio and sometimes DC power as well.

Some computer sound cards have an additional stereo input labeled “line in.” This is designed to accommodate the stereo signal from a VCR, CD player, or tape deck, and is not suitable for use as a microphone input. However, if you decide to purchase a mic-to-line preamplifier or a mixer with a line or aux output, the line input of the computer would be the ideal interface for that equipment.

Dynamic versus condenser mics
Different types of microphones use different methods of converting the acoustic energy created by a sound source (such as your voice) into electrical energy that can be amplified, processed, recorded, or transmitted.

The two most popular types of microphones for professional use are the dynamic and the condenser (sometimes called an electret). The primary difference —as far as computers are concerned —is that condenser microphones require a source of dc power to operate. Dynamic microphones do not require any external powering.

The type of power needed by the condenser microphone and the way that it is provided are important issues that may affect whether a particular professional microphone will work with a particular computer, and how the cable connecting them together should be configured. The type of power provided by most computer mic inputs is called bias voltage and it provides powering for a small transistor inside the microphone element or ‘head’.

The type of power provided at the input of mixers and other professional equipment is called phantom power, and is used to power additional circuitry found in condenser microphones. This circuit, also called preamplifier, may be housed inside of the microphone handle or, in the case of small lavalier or gooseneck microphones, in an external tube or pack. [NOTE: the preamplifier used by professional condenser microphones is not the same as the microphone-to-line amplifier mentioned earlier, which also goes by the name ‘preamplifier’.]