Analog Modeling: How Plugins Get That Sound

"Analog warmth." "Vintage character." "That console sound."

You've seen the marketing. But what's actually happening inside analog-modeled plugins? What are they doing to your audio?

As someone who builds plugins, I can tell you: it's not magic. It's math, physics, and a lot of careful engineering. Understanding what these plugins do helps you use them better.

What Makes Analog Sound "Analog"?

Analog gear doesn't just pass audio through unchanged. Every analog circuit adds something to the signal:

Harmonic Distortion

When audio passes through analog components (tubes, transistors, transformers), it creates harmonics—additional frequencies that weren't in the original signal.

These harmonics are mathematically related to the original frequency:

2nd harmonic: Double the frequency (one octave up)
3rd harmonic: Triple the frequency (octave + fifth)
4th, 5th, etc.: Higher multiples

The balance of these harmonics creates the "character" of the gear.

Frequency Response Variations

No analog circuit has perfectly flat frequency response. There are subtle rolloffs, bumps, and dips. Transformers roll off extreme highs and lows. Capacitors have resonances.

Dynamic Response

Analog circuits behave differently depending on how hard you drive them. Push a tube harder and the distortion increases. This level-dependent response creates a "feel" that's different from digital.

Noise

Analog gear has noise floors, hiss, hum. Modern plugins often don't model this (thankfully), but vintage gear certainly had it.

Tubes vs. Transistors vs. Transformers

Different components create different harmonic profiles.

Tube Distortion

Tubes (valves) produce primarily even harmonics (2nd, 4th, 6th).

Even harmonics are musically related to the fundamental—they're octaves and octave-fifths. They sound pleasant, warm, full.

This is why tube gear is described as "warm" and "musical." The distortion it adds is harmonically flattering.

Transistor Distortion

Transistors tend to produce more odd harmonics (3rd, 5th, 7th).

Odd harmonics create dissonance. They sound buzzy, edgy, aggressive.

This isn't necessarily bad—sometimes you want edge. But it's why "solid-state" often sounds harsher than tubes.

Transformer Saturation

Transformers add a bit of both, plus they have their own frequency response curve (rolling off lows and highs), and they add a type of compression.

The "transformer sound" is a combination of gentle saturation, frequency shaping, and dynamic behavior.

How Plugins Model This

Component-Level Modeling

The most accurate approach: model each electronic component individually.

Analyze the actual circuit of a Pultec EQ or LA-2A compressor. Model every resistor, capacitor, tube, transformer. Simulate how they interact.

This is computationally expensive but produces the most accurate results.

Transfer Function / Waveshaping

A simpler approach: measure how the hardware responds to different input levels and create a mathematical function that matches.

Feed the hardware a test signal, measure the output, create an equation (waveshaper) that transforms input to output the same way.

Faster to run, less accurate to the real behavior, but often close enough.

Convolution

Measure the impulse response of the hardware and apply that to incoming audio.

Common for modeling rooms, cabinets, and some EQs. Limited because it only captures linear behavior—it can't model level-dependent distortion.

Machine Learning

Train neural networks on input/output pairs from the real hardware. The network learns to mimic the behavior.

Relatively new approach. Can capture complex nonlinear behavior but requires massive training data and can produce unpredictable results.

What This Means for You

Analog Modeling = Harmonic Distortion + Frequency Shaping

When you add an analog-modeled plugin, you're adding:

Harmonic distortion (subtle or not so subtle)
Frequency response changes
Dynamic response (compression-like behavior)

If you don't need these, you don't need the analog modeling.

Drive/Input Controls Matter

Many analog plugins have input or drive controls. These control how hard you're "hitting" the virtual circuit.

Low input: Minimal distortion, mostly frequency character
High input: More harmonics, more saturation, more squash

Don't just set it and forget it. The input level is a major part of the sound.

Too Much Analog Modeling = Mud

Every analog-modeled plugin adds harmonics. Stack too many and you've got a buildup of distortion, particularly in the upper harmonics.

This leads to harshness, fizziness, and mud.

Be selective. You don't need analog modeling on every channel.

Plugin Order Matters

Distortion before EQ sounds different than EQ before distortion.

If you high-pass, then saturate, you're saturating a signal without much low end.

If you saturate, then high-pass, you're generating low harmonics then filtering them.

Think about what you're feeding into the harmonic generation.

Common Plugin Types

Analog-Modeled EQs

These combine frequency shaping with transformer/tube coloration.

Pultec style: Tube warmth, transformer rolloff, inductor resonance
Neve style: Transformer saturation, musical frequency curves
SSL style: Clean but with console character

The same EQ curve from a "clean" digital EQ vs. an analog-modeled one will sound different because of the harmonic content.

Analog-Modeled Compressors

Beyond compression, these add:

Tube compressors (LA-2A): Smooth, warm compression with harmonic saturation
FET compressors (1176): Fast, punchy, transistor edge
VCA compressors (SSL): Clean but with transformer character

The compression behavior itself is modeled (attack, release, knee), plus the harmonic/transformer aspects.

Tape Emulation

Tape machines add:

Compression: Tape naturally compresses transients
Saturation: Harmonics increase with level
High-frequency rolloff: Tape rolls off extreme highs
Wow and flutter: Pitch variations (optional)
Hiss: Tape noise (usually optional)

Tape plugins are complex because they model a mechanical system, not just electronics.

Console Emulation

Channel strip and summing plugins model:

Preamp coloration: Often transformer and/or tube character
Summing behavior: How channels combine in the analog domain
Crosstalk: Bleed between channels (subtle)

Do You Need Analog Modeling?

When It Helps

Thin, digital-sounding sources: Analog modeling adds body
Harsh high frequencies: Even harmonics can smooth things
Sterile mixes: Character and "glue"

When It Hurts

Already saturated sources: More saturation = mud
Clean productions: Not every genre needs warmth
CPU-limited sessions: Some models are heavy

The Hybrid Approach

Use analog-modeled plugins where they add value (bus compression, key channels). Use clean plugins where you need precision (surgical EQ, transparent limiting).

You don't have to choose all one or all the other.

A Note on "Analog Warmth" Marketing

Not every plugin labeled "analog" or "vintage" actually does much.

Some are just EQs with non-flat curves. Some add a tiny amount of saturation that's barely audible. Some are just regular digital plugins with wood paneling on the GUI.

Trust your ears. Does it actually sound different? Better? Does it add something you need?

If you can't tell the difference with the modeling engaged vs. bypassed, you might not need it.

The Bottom Line

Analog-modeled plugins add harmonics, shape frequency response, and respond dynamically to level. They're not magic—they're controlled distortion and filtering.

Use them intentionally:

Know what character you're adding
Drive them appropriately
Don't stack too many
Use clean tools when you need precision

Understanding what these plugins actually do helps you make better choices about when to use them.