Feed Forward vs Feedback Compression: What's the Difference?

If you've ever wondered why an 1176 feels different from a dbx 160—even with identical settings—the answer lies in their fundamental architecture. Feed forward and feedback compression represent two philosophically different approaches to dynamics control, and understanding this distinction will change how you hear and use compressors forever.

This isn't just academic theory. Once you understand what's happening under the hood, you'll make faster, more intentional decisions about which compressor to reach for and why.

The Core Difference: Where the Detector Listens

Every compressor has two main jobs: detect the signal level, then reduce gain when that level exceeds the threshold. The fundamental difference between feed forward and feedback designs is where the detection happens.

Feed Forward: The detector listens to the input signal—before any gain reduction occurs.

Feedback: The detector listens to the output signal—after gain reduction has already been applied.

This single architectural choice cascades into dramatically different sonic behaviors.

Feed Forward Compression: Transparent and Solid

In a feed forward design, the compressor knows exactly what's coming. It sees the input signal, calculates precisely how much gain reduction is needed, and applies it.

Characteristics:

• Transparent and discrete — compression without obvious color
• Solid, defined response — predictable and repeatable
• Preserves low end — less interaction with bass and sub frequencies
• Clean and surgical — excellent when you want control without changing the tone
• Modern sound — what you put in is what you get out, just controlled

Classic Feed Forward Compressors:

• dbx 160 (and descendants)
• Elysia Alpha (in feed forward mode)
• API 2500 (in "New" mode)
• Most modern VCA compressors
• Most digital compressors and limiters

When to Use Feed Forward:

• When the low end is already balanced and you don't want to disturb it
• Transparent bus compression where you want control without color
• Peak limiting and loudness maximization
• When you need surgical precision without vibe
• Fast transient material where you need immediate response

Feedback Compression: Color and Glue

In a feedback design, the compressor is constantly reacting to its own output—a continuous self-correcting loop that creates more complex, program-dependent behavior.

Characteristics:

• Dirty and colorful — adds harmonic character and vibe
• Glue effect — makes elements feel like they belong together
• Eats bass and sub — naturally tames low frequency energy
• Musical and forgiving — reacts differently to different material
• Vintage sound — the classic "compressed" tone

Classic Feedback Compressors:

• Teletronix LA-2A (and most optical compressors)
• Universal Audio 1176
• Fairchild 670
• Neve 33609 / 2254
• SSL G-Series Bus Compressor
• API 2500 (in "Old" mode)
• Most tube and optical designs from the 1950s-70s

When to Use Feedback:

• Mastering tracks with too much sub/bass — it'll naturally tame the low end while glueing everything together
• When you want the mix to feel more cohesive
• Adding warmth and character
• When "vibe" matters more than transparency
• Bus compression where you want musical "glue"

How Each Topology Handles Low End

One of the most practical differences I've observed in mastering is how each topology interacts with bass and sub frequencies.

Feed forward compression tends to preserve the low end. It's transparent and discrete—what goes in comes out, just controlled. If your low end is already balanced, feed forward keeps it that way.

Feedback compression interacts more aggressively with bass and sub. It eats into those frequencies while simultaneously creating that coveted "glue" effect. This makes feedback compression an excellent choice when a track arrives with an overpowering low end—you're solving two problems at once: taming the bass and adding cohesion.

When I have a mix with too much sub, I'll often reach for feedback compression before touching an EQ. It's a more musical solution than surgical cuts.

Why This Matters in Practice

Let's say you have a drum bus with sharp transients. Here's how each approach handles it:

Feed Forward Response: The compressor sees the transient coming, immediately calculates the required gain reduction, and applies it precisely. The transient is controlled, the compression is audible and defined, and the low end remains largely intact.

Feedback Response: The compressor applies some reduction, checks the output, realizes it's still hot, applies more, checks again. By the time it's "caught" the transient, some of it has passed through. The result is softer, more forgiving compression that lets some transient energy breathe—but the bass and sub get worked harder in the process.

Neither is "better." They're different tools for different intentions.

The Hybrid Approach

Some modern compressors let you switch between modes or blend them:

• API 2500 — "Old" (feedback) vs "New" (feed forward) switch
• Rupert Neve Designs Portico II / 5043 — FF/FB toggle
• Elysia Alpha — Offers both topologies
• SSL Bus+ — Feed forward/feedback switching

In my mastering chain, I use both approaches strategically. Feed forward when I need transparent control and want to preserve a balanced low end. Feedback when I want glue, character, and natural bass taming.

Quick Reference

Feed Forward:

• Character: Transparent, solid, discrete
• Low End: Preserves bass/sub
• Response: Precise, immediate
• Transients: Tight control
• Sound: Clean, modern
• Best For: Balanced mixes, transparent limiting

Feedback:

• Character: Dirty, colorful, glue
• Low End: Eats bass/sub
• Response: Musical, self-correcting
• Transients: Some punch passes through
• Sound: Warm, vintage
• Best For: Bass-heavy tracks, cohesion, vibe

Listening Exercise

Here's how to train your ears:

Find a compressor with both modes (API 2500 plugin, Neve Portico, or similar)

Set moderate compression — 4:1, medium attack, medium release, 3-4dB reduction

Switch between feed forward and feedback on the same material

Listen for how transients hit differently, the "tightness" vs "looseness" of the compression, how the compressor interacts with the low end, and how the compressor "breathes" with the music

Once you hear it, you can't unhear it. And you'll start recognizing these characteristics in every compressor you use.

The Bottom Line

Feed forward compression gives you precision, transparency, and preserves your low end. Feedback compression gives you musicality, glue, and naturally tames excessive bass.

Neither is superior—they're complementary tools. The best engineers don't pick a favorite; they understand both approaches deeply and reach for the right one at the right moment.

Know your tools. Trust your ears. Let the music guide the choice.