From Hydrogenaudio Knowledgebase
 Microphones for Computers
This text addresses matching microphones to computers and requirements. Solutions described here are oriented to users and constrained to solutions that work with GNU compatible kernels.
First characteristics of the components are described, then combinations of components for use.
 Computer inputs
Analog inputs and outputs on computers use Tip, Ring, and Sleeve (TRS) type connectors. The microphone connector is a TS connector, headphones are TRS.
 Microphone input
A microphone connected to this input socket is routed to an internal preamplifier then analog to digital converter (ADC). The connector socket is marked with pink.
 Line input
Connects to ADC. The connector socket is marked with light blue.
 Converting audio to electrical signals
Common microphones convert audio into electrical signal in 1 of 2 ways: dynamic or condenser.
do not need power.
Some condenser microphones use electrets and are called “electret microphones“.
needs power and can be powered by
- the cable which also carries the audio signal. This is called 'phantom power'. The power is 48V or 12V for low impedance and 3V to 5V for high impedance.
 Connection or wiring schemes and electrical characteristics
There are 2 sets of schemes which we will refer to by impedance. The impedance has otherwise no significance to the consumer.
 Low impedance
Connectors are XLR.
Electrically balanced. Two signal wires are the inverse of each other relative to a ground connection.
 High impedance
Connectors are ¼ inch TS plugs which have 2 electrical connections on the plug.
Electrically unbalanced. 1 connection is the Tip, the other is the Sleeve.
 Mixing Impedances
A low-to-high impedance transformer is the proper way to make the connection between low and high impedance devices. You will also need a ¼ inch to 1/8 inch adapter.
 Connection combination schemes in order of decreasing audio fidelity.
Dynamic or condenser with battery low impedance microphone to mixer to line in. A microphone can connect to line input after being processed by a preamplifier or a mixer which contains a preamplifier. Mixers are only a little more expensive than preamplifiers and provide phantom power.
Low impedance microphone not needing phantom power to transformer to line in.
High impedance microphone to microphone in.
 unix, including GNU, based OSes
There are 2 sound driver systems for Linux: ALSA and OSS. Some microphones with USB output function with ALSA. (Evidence) IEEE 1394 (a.k.a. Firewire, iLink) is not supported. No sound device providing XLR is supported.
 Notes and references
A low-to-high impedance transformer example.