Audio 101 – Gain Structure

When installing an audio system or starting a mix, the very first thing to consider—even before the equipment itself—is Gain Structure: matching signal levels properly across every piece of equipment in the chain.

You may have encountered situations like these:

• The instruments sound fine, but you struggle to push the lead vocal or solo instrument above the mix.

• The overall sound lacks punch and energy, sounding harsh or excessively noisy instead.

• The amplifiers are turned all the way up, yet the volume still feels surprisingly low.

If we were to summarize Gain Structure in a single sentence, it would be:

"The series of steps taken to send an appropriate input level to the amplifier at an appropriate output level, delivering an appropriate listening level to the audience."

To set a proper reference, we first need to know what constitutes an "appropriate level."

The following target levels serve as a solid baseline.

(Since digital consoles are the norm today, we will use dBFS as our unified standard.)

1. Setting Input Levels: In a live band setup, adjust the mic preamp gain (or use Clip Gain in a DAW) so that the kick drum averages around -18 dBFS. For other genres, use whatever foundational instrument serves as the core reference.

2. Balancing the Rhythm Section: Align the bass and snare relative to the kick, establishing the core instrumental balance before moving on to panning.

3. Utilizing Headroom: Because the core mix sits at an average level of -18 dBFS, you maintain -18 dB of headroom. This headroom gives you the necessary space to bring lead vocals or solo instruments forward in the mix without clipping or crowding.

4. Calibrating Output & Monitoring: Adjust the input gain on your amplifiers so that this -18 dBFS average mix yields 85 dB SPL-A at the optimal listening position—for both stage monitors and the Front of House (FOH) main system.

5. System Tuning: If the setup involves multiple speaker enclosures and subwoofers, this calibration can be performed during or immediately following system tuning (crossover configuration, EQ, and time alignment) via a system processor.

Summary

The foundational rule of Gain Structure is configuring the system so that an input level averaging -18 dBFS translates to a listening level of 85 dB SPL-A in the space.

It is a simple concept, but assuming the venue is equipped with adequately sized speakers, proper gain staging ensures the overall system operates stably at roughly 80% to 85% of its maximum power capability.

Step In!:

Why 85 dB SPL-A?

Human hearing does not perceive all frequency ranges equally across different volume levels. Sensitivity varies across the frequency spectrum, particularly showing dynamic shifts in low and high frequencies.

At around 85 dB SPL-A, the human ear perceives frequency response most uniformly across the audible spectrum. For this reason, 85 dB SPL-A serves as the standard reference level for calibrating audio systems across both recording studios and live performance venues.

By Lindosland - Transferred from en.wikipedia to Commons., Public Domain, https://commons.wikimedia.org/w/index.php?curid=2565926