From Echoes to Reverb

Reverb is not one mysterious effect. Start with a sound, create delayed reflections, let them recirculate, diffuse them, and damp them — eventually the echoes become a dense reverberant field.

You already know every block in this machine.
STORE → MULTIPLY → ADD → FEEDBACK → FILTER → ALL-PASS DIFFUSION

1. Build the reverb one idea at a time

Use the same snare hit and add one stage at a time. Watch the timeline below change as the sound becomes more complex.

Left = direct sound. Discrete spikes = early reflections. Dense cloud = late reverberant field.

2. Where do the delays come from?

A real room sends sound to the listener by many paths. Longer paths arrive later and usually quieter.

1.00×
The room does not contain a “reverb processor.” It contains many different path lengths. DSP imitates that behaviour using delay lines, gains, feedback, filtering and diffusion.

3. Turn the room into DSP

INPUT │ ├── DIRECT ───────────────────────────────────────┐ │ │ └→ DELAYS → GAINS → FILTERS → FEEDBACK → ALL-PASS │ ├→ Σ → OUTPUT │ more paths / more density ─┘

This is a reverb algorithm

The particular set of rules used to connect the delays, gains, filters, feedback paths and all-pass sections is a reverb algorithm.

Different designers can use the same basic DSP building blocks but arrange them differently, choose different delay times, feedback relationships, filters and diffusion structures — producing different reverberant behaviours and sounds.

Same building blocks. Different rules and topology. Different reverb algorithm.

DELAY
STORE
Different path lengths become different delay times.
GAIN
MULTIPLY
Reflections lose energy as they travel.
MIX
ADD
Direct sound and reflections are summed.
DECAY
FEEDBACK
Energy is recirculated so reflections continue.
DAMPING
FILTER
High frequencies usually die away faster.
DIFFUSION
ALL-PASS
Discrete reflections are redistributed into a denser field.

4. Reverb controls — what are they actually doing?

Now manipulate the underlying ingredients directly. The transport is repeated here so you can stay with the controls and listen while you work. Playing from this section automatically switches on the complete reverb algorithm.

7
0.62
68%
1.00×
5.20 kHz
18 ms
42% wet
Try this: set Diffusion near zero and use a short decay — you should hear separate echoes. Then increase Reflection count, Feedback and Diffusion until the echoes stop sounding like individual events.

What are these controls actually changing?

Reflections
The number of different delayed paths representing sound arriving from different surfaces and routes through the simulated room.
Decay / Feedback
How much reverberant energy is recirculated through the network. More feedback generally produces a longer decay.
Diffusion
Increases the density and temporal complexity of the reflections, helping separate echoes merge into a smoother reverberant field.
Damping
Filtering in the reverberant paths. Lower settings remove high-frequency energy more quickly, producing a darker tail.
Pre-delay
The time between the direct sound and the onset of the reverberant field. It helps control the perceived separation between source and room. In production, more pre-delay can also make the direct source feel more distinct or forward while the room sits behind it.
Dry / Wet
The balance between the original direct sound and the reverberant output.
Room Size
In this simplified model, this scales the delay-time relationships representing path lengths. Larger settings generally make reflections arrive later and farther apart.

5. Direct → echoes → reverberant field

Low density

SNARE │ ├──── 18 ms ├──────── 31 ms └──────────── 47 ms You hear: separate reflections.

High density

SNARE │ ├─╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱╲╱ └─::::::::::::::::::::: You hear: a continuous tail.

At some point, “many echoes” becomes “reverb.”

There is no magical boundary. It is a change in reflection density, decay and temporal complexity.

6. Remember the all-pass filter?

On the previous page it looked almost perverse: flat magnitude, changing phase. In a reverb network that becomes useful because all-pass sections can redistribute energy in time and increase diffusion without simply imposing an EQ curve.

EARLY REFLECTIONS │ ▼ ALL-PASS → ALL-PASS → ALL-PASS │ ▼ denser / smoother tail
Same little operations, different topology. This is why we learned delay, feedback, filters and all-pass separately before attempting reverb.

7. What this page is — and is not

This is a deliberately simplified algorithmic reverb model designed to make the building blocks audible and visible. Real reverbs may use more sophisticated comb networks, feedback-delay networks, modulation, decorrelation, frequency-dependent decay and many other design choices.

Next: build a more complete algorithmic reverb, then compare it with convolution — where the “filter coefficients” can literally be the samples of a measured room impulse response.