Jan Zurcher is a singer-songwriter who lives in Friday Harbor, Washington. The document discusses reverb, which refers to reflections of sound waves that reach the listener's ears at different times, creating echoes. There are two main types of reverb: algorithmic reverb, which uses computer algorithms to model reflections; and convolution reverb, which convolves the input signal with an impulse response sample of a real space. Both reverb types aim to create the illusion that a sound was recorded in a particular room or space.

1. Hi. My name is Jan Zurcher.
I’m a singer-songwriter living in a
small town called Friday Harbor, San
Juan Island, Washington
This lesson is for Week 5 of the
Introduction to Music Production
Course at Coursera.org.
The topic I have chosen to look at
this week is…

3. What is reverb?
Before you start to try to control
reverb in your DAW, it is important to
first understand what “reverb” is.
“Reverb” is short for reverberations –
or reflections of sound waves that
usually continue on as a series of
echoes. This happens because the
reflected sound waves reach the ears
of the listener at different times.
Suppose that you are standing in a
room directly in front of a sound
source. As you can see, the direct
sound arrives at the listener’s ears
first.
Reflected sounds arrive at different
times depending on how far the signal
travels to reach the reflective surface
and then the listener’s ear.
Sound
Source
Person
Direct
Sound

4. The Direct Sound is known as the “Dry signal”.
The Reflected Sound in known as the “Wet signal” and is really a very large number of
varying echoes resulting from the signal bouncing around off a variety of surfaces before
reaching the listener.
Different sized rooms with
different wall, ceiling and floor
surfaces will all have different
reverberation patterns but
they will all be made up of the
components shown in the
graph on the right – the signal,
discrete reflections and a
diffuse reverb tail.
Image from Logic Express 9.0 help manual.
What is reverb?

5. In the early days of recording, reverb was managed by recording in rooms of different sizes
or different wall surfaces – sometimes hard (like cement) and sometimes soft (like
curtained) and sometimes by hanging metal plates, etc.
In modern recordings, digital devices are often used to imitate the sound of a given space.
In general, there are two types of devices used:
Algorithmic reverbs Convolution reverbs
What is reverb?

6. Algorithmic Reverb
An algorithmic reverb device gets its name from the fact that it uses algorithms
– step by step instructions to the computer – to simulate or digitally “model”
different types of reverberations. It’s like creating a “software recipe” for the
type of reverb that you want to create.
These devices are used to:
• create a specified number of reflections,
• add pre-delay to simulate a specific room size,
• adjust the high frequency damping; and,
• control other factors such as the diffusion tail
all based on an understanding of the way sound interacts with physical spaces.
Let’s take a look at some of the key components of an Algorithmic Reverb
device found in Logic Express 9.0 – Gold Reverb

7. An algorithmic reverb device has two main sections:
1. The Early Reflections section

8. And,
2. The Reverb Section

9. The main parameters controlled in the Early Reflection section include:
1. Pre-delay – set the amount of time (from 0 to 200 ms) between the start of the
original signal and the start of the early reflections. Generally, set this at a level just
below where you start to hear an audible echo.
2. Room Shape - select the number (from 3 to 7) of reflective “walls” used in the
algorithm.
3. Room size – set the length (from 1 m. to 200 m.) of the walls in the room
4. Stereo Base –set the distance (from 0 to 2 m) between the two “virtual ears” used to
capture the signal in the simulated room. In general, for the best sound, set this to be
a little bit farther apart than the distance between the ears on a person’s head.

10. The main parameters controlled in the Reverb section include:
1. Initial Delay – set the time (from 0 to 200 ms) between the start of the original signal and
the start of the diffuse reverb tail. In general, set this as long as possible but without a gap
between the early reflections and the tail.
2. Spread – set the stereo image for the reverb – 0% is mono and 200% means the stereo is
artificially expanded.
3. High Cut – set a value (between 1,200 and 12,000 Hz). Frequencies above that are filtered
from the reverb signal. This lets you imitate the effect of less reflective surfaces (e.g.,
wallpaper or carpet).
4. Density – set the density (for 0 to 100%) of the diffuse reverb tail. In general, set the signal
to be as dense as possible; a Density value that is too low can make the reverb tail sound
grainy.
5. Reverb Time - set the time (from 0.5 to 20 seconds) it takes for the reverb level to drop off.
Small rooms or those with absorbent surfaces have a reverb time of 3 seconds or less;
large, empty rooms can be 8 seconds or more.

11. In the Extended Parameters area is:
Diffusion - Sets the diffusion (0 to 100%) of the signal (how close or far apart the
early reflections are) which impacts the “thickness” of the reverb tail. Higher
values mean the reflections are closer together and this results in fewer changes
in level, times, and pan position over the length of the diffuse reverb signal (i.e.,
the decay).

12. Algorithmic Reverb – Common Settings
http://www.planetoftunes.com/record/reverb.html
Pre-delay Reverb Time Diffusion High
Frequency
Decay
Bathroom 50 ms 0.5 sec 5-10% 0
Sitting Room 10 ms 0.25 sec 25-40% Lots
Concert Hall 50 ms 2.5 sec 85-100% Lots
Cathedral 100 ms 5 sec 85-100% Little
Different combinations of the various parameters in the Early Reflections
and Reverb sections can create the illusion of different spaces:
More complex algorithmic reverb devices have other controls that allow even
more capabilities to shape the reverb but the ones discussed here cover the most
common.
Now, let’s look at Convolution Reverb…

13. Convolution Reverb
Convolution reverbs use an entirely different technique to create the sense of
“space”.
They use actual sounds recorded in actual spaces by using multiple microphones
to capture the acoustic characteristics of that particular space (that is, all of the
reflections in that room after an initial signal). These samples are called “Impulse
Responses”.
When you feed a signal into a Convolution Reverb, the computer uses complex
(or convoluted) mathematical equations to combine your signal with the
selected Impulse Response to generate output that makes it sound as though
your signal was actually recorded in the specified space.
Basically, it filters your sound through the Impulse Response so that the sound
decays (that is, has diffuse reverb tail) in a way that matches the way it would
actually decay in that type of room or space.

14. Convolution Reverb
The first step in using a Convolution Reverb is selecting the Impulse Response (the
kind of space) that suits your needs. Often that is all you need to do.
However, today’s sophisticated and full featured Convolution Reverbs allow you a
great deal of control over your sound.
Space Designer, which comes with Logic Pro, allows control over a number of
different parameters: Impulse Response, Envelop and Equalization, Filters as
well as many others. This enables you to take the basic sound of the space
and adjust it to meet your needs. Unfortunately, Logic Express does not
include a Convolution Reverb, so I cannot provide details on this device.

15. Reverb Types – Key Differences
Algorithmic Convolution
Technologies Computer generated based on
manually set parameters
Based on samples of real spaces
Controls Manipulate parameter such as room
size, number of walls, etc.
Select a desired room type from
Impulse Response list
Use for: Adding sounds to full mixes
Creating ambiences on symphony or
string ensembles
Sampled instruments
Solo instruments
Instruments that are not sampled
Where essential to create a
convincing illusion of a space
Avoid using
for:
Solo instruments Multiple instruments (ensembles) –
can create “muddiness” in the sound
CPU Usage Moderate Very high due to complexity of
calculations – use sparingly
Other Considered by some to be very
flexible
Considered by some to allow more
creativity and allow for more
experimental sound design

16. Reverb – Summary
Reverb is a very complex concept and creating effective reverb in
your mixes takes a great deal of practice.
It also takes a “light” hand. Reverb should be a subtle effect that
sits in the background – barely noticeable. It is about creating an
illusion of space not about standing out in your mix.

17. 1. http://www.emusician.com/Default.aspx?tabid=273&EntryId=671
2. http://www.briandoyle.com/2011/10/28/convolution-vs-
algorithmic-reverbs/
3. http://www.prorec.com/2012/03/reverb-types-
explained/#sthash.i9OQyyUY.dpuf
4. http://www.softube.com/index.php?id=predelay_diffusion
5. http://www.prorec.com/2012/03/reverb-types-explained/
6. http://www.emusician.com/Default.aspx?tabid=273&EntryId=671
7. http://prorecording.org/blog/2013/04/the-difference-between-
algorithmic-and-convolution-reverb/
8. Logic Express 9.0 Help Manual
9. Lecture video from Introduction to Music Production
References