The collection of extraneous noise. This can be a concern, especially in amplified performances, where audio feedback can be a significant problem. Alternatively, it can be a desired outcome, in situations where ambient noise is useful (hall reverberation, audience reaction.)
Choice of a signal type: Mono, stereo or multi-channel.
Type of sound-source: Acoustic instruments produce a very different sound than electric instruments, which are again different from the human voice.
Situational circumstances: Sometimes a microphone should not be visible, or having a microphone nearby is not appropriate. In scenes for a movie the microphone is kept above the pictureframe, just out of sight. In this way there is always a certain distance between the actor and the microphone.
Processing: If the signal is destined to be heavily processed, or "mixed down", a different type of input may be required.
The use of a windshield as well as a pop shield, designed to reduce vocal plosives.

Basic techniques

There are several classes of microphone placement for recording and amplification.In close miking, a directional microphone is placed relatively close to an instrument or sound-source. This serves to eliminate extraneous noise-- including room reverberation-- and is commonly used when attempting to record a number of separate instruments while keeping the signals separate, or when in order to avoid feedback in an amplified performance.
In ambient or distant miking, a sensitive microphone or microphone is placed at some distance from the sound source. The goal of this technique is to get a broader, natural mix of the sound source or sources, along with reverberation from the room or hall.

Stereo recording techniques

There are two essential components that the stereo loudspeakers need to place objects (phantom sources) in the stereo sound-field between the loudspeakers. These are level difference ? L, the relative loudness, and time-delay difference ? t, the difference in arrival time. The "interaural" signals (binaural ILD and ITD) at the ears are not the stereo microphone technique signals which are coming from the loudspeakers, and are called "interchannel" signals (? L and ? t). Do not mix these sort of signals. Loudspeaker signals are never ear signals and vice versa. Read the header "Binaural recording for earphones".