Basic mixing and recording principles apply regardless of the sophistication (or lack thereof) of the equipment being used. One microphone in a room recording still works fine, as long as the microphone is located in the right place. The first consideration is the natural soundscape within a room, meaning how sounds are detected, where they are stronger and how they move across the room. Corners are a natural "vacuum cleaner" for sound, and sound waves will collect in corners (this is called absorption) unless baffles (acoustic panels, for example) are strategically placed there to soak up or deflect the sound. This is especially true for low frequencies that basses and kick drums produce.
Another consideration in room sound is reverberation, or the repeating of a sound wave. Reverb and echo are useful effects in mixing and recording, unless they are unwanted or unexpected. Mid-range and higher frequencies, especially the sharp, percussive sound waves produced by snare drums, amplified guitar string attacks and even some vocal effects will naturally reverberate in certain areas of a room, resulting in a "slap-back" repeating effect. Reverberation and absorption characteristics are unique to each room, and testing for these aspects before mixing and recording are a wise move.
Mixing is where the real work is done before the recording process begins. This is the engineer's chance to experiment with the volume and tone (EQ) levels of each voice and instrument. The placement of the voice or instrument in the mix is also very important. The standard approach is: vocals and drums in the center, bass a little to the left or right,and guitars everywhere else (more or less). It depends on the type of song and the genre of the music, and some mixing techniques try moving the instruments and the vocals around to create a different "mood" for the listener. This is known as panning (a derivation of the word "panorama"), and it refers to placement of the sound throughout the left and right channels of a stereo mix. It is used most often for guitar mixing. For instance, a clean guitar and a distorted guitar can be placed on opposite sides of the stereo spectrum equally, to create a full but multilayered sound, especially when the guitars play the same parts.
The advent of digital sound effects has dramatically changed the way mixing and recording is done. Previously, the natural dynamics of a room were maximized for echo, bass response and other characteristics. Digital processors of today attempt to recreate these aspects and more. Overall, they do accomplish their tasks, as long as the engineer is familiar with their operation. Yet one of the most frequent complaints of listeners to modern recordings is the overuse of digital processing.
The key to effective signal processing is "less is more," in most cases. The quality of the mixing and recording equipment has an effect on the resulting tracks, and the better mixers and recorders tend to portray sound processing better overall. Anyone can create a quality recording with limited equipment, however. A small amount of "slap-back" echo on a snare drum can nearly convince the listener that they are hearing more than one drum. Just a little chorus effect (a "wavy" sound) on a guitar or even a vocal can fill the soundscape with rich tones that can make a four-track recording sound like 24 tracks.