Spatial crowding can occur if there are too many parts clashing within the same areas of the stereo image. Frequency crowding can occur if there are clashing sounds with similar tones (such as a screeching sax and vocal).
It is important to create differentiation between different parts, especially in songs with crowded arrangements. Spatial differentiation is achieved by placing instruments into different positions within the stereo image, or by having some parts moving rather than stay in one place.
Frequency differentiation can be achieved by EQing sounds to emphasize more of their differences rather than similarities. For example, both a kick drum and a bass will have very low sounds, but the kick will also have a sharp attack that will cut through the sound of the bass, and the bass will have a sustained roundness that will continue between kick hits.
Changing instrument volumes is an important process to consider when trying to create mixes with clarity, within which all of the instruments can be clearly heard and felt according to their functions.
Some mix engineers try to create differentiation by equalizing each sound to fit into a narrow frequency range. This works, but results in mixes that are significantly less expressive than mixes that contain full sounding instruments that move forward or back in the stereo image, either taking over the image or creating space for other instruments to take over.
Static changes to sound are changes that remain the same throughout an entire mix (“set it and forget it”). Dynamic changes are changes that are adjusted to different settings through the course of the mix. Anything can be dynamic, and almost every mix involves increasing and decreasing channel output volumes, panning or even if the channel output is turned on or off (“muted”).
The most commonly dynamic element is channel output volume. Channel output volume is usually accessed by a sliding fader rather than by a rotary knob. During a song as the volume of a channel is increased and decreased, the channel fader will move up and down. During a song as a channel is turned on or off, the mute switch will open and close.
These changes can be done by hand, but then they need to be performed every time that mix is played. As a result, in the days when changes had to be performed by hand it was not unusual to see many people crowded over a console, each with a specific job to do at a certain part of the song.
For example, when the singer says the word “baby” perhaps one person would turn a knob to make the voice sound different than it sounded for every other word. Perhaps when the song ended there was one instrument that kept playing that had to have its channel turned off (muted) every time the song reached the end.
Many consoles allow you to record the changes that you make to knobs or faders and play the changes back. This automation allows you to make changes to a channel along with the music only once and have them play back so you are free to change another track. For example, you can mute a vocal track when the singer coughed while recording, and have the Automation automatically perform the mute for you whenever the song is playing.
Automation is usually used for volume faders or send knobs, but many effects allow you to automate settings as well.
Bruce A. Miller is an acclaimed recording engineer who operates an independent recording studio and the BAM Audio School website.