A GENTLE INTRODUCTION TO SONIC IMMERSIVITY
WORKSHOP #1 | AMBISONIC WORKFLOW IN REAPER
Session dates (Lisbon Time):
Introductory session | 04.11 | 18h-20h
Hands-on session | 11.11 | 18h-20h
Showing works | 18.11 | 18h-20h
Thank you for participating in this workshop.
We will use this forum post as our main communication system, in this way the whole workshop will be documented in “real-time”. I will be informing you about all aspects through here by editing the post.
The spirit of this small series of workshops is to share our knowledge, so if you have any previous experience using DAWs or working with spatial sound please share here (with comments) and don’t be afraid to speak actively through our 2 sessions, it will be very appreciated.
The link for the sessions will be shared through here too, and will be open to more people if they want to listen.
We will start by installing Reaper and 3 plug-ins packages that can be used to work with ambisonics and spatialization. (Don’t worry right now about what ambisonics is, we will get into it.)
Please install all things before our session, and if you have any issue just send me a DM and I will help you out. But the installs are pretty straightforward, so don’t be scared and do it as soon as possible
Extra: (only if you have time for)
What is Ambisonics?
is a method of codifying a sound field taking into account its directional
Ambisonics is a perturbative theory where each channel has information
about certain physical properties of the acoustic field, such as the pressure or
the acoustic velocity.
Ambisonics is a Perturbative Theory
At zeroth order, Ambisonics has information about the pressure field at the
origin (recording of an omnidirectional microphone at the origin). The channel
for the pressure field is conventionally called W.
At first order (FOA), Ambisonics adds information about the acoustic velocity
at the origin (recording of three figure-8 microphones at the origin, along each
one of the axis). These channels are called X,Y,Z. Following the Euler equation,
the velocity vector is proportional (up to some equalization) to the gradient of
the pressure field along each one of the axis.
At second and higher orders (HOA), Ambisonics adds information about
higher order derivatives of the pressure field.
Ambisonics 3D polar patterns
Features of Ambisonics
• Based on physical principles of the acoustic field.
• Not restricted to single plane waves, but it can account for any general sound field.
• Completely layout-independent, in the sense that the Ambisonics production and postproduction workflow does not depend on the exhibition layout. Stereo and traditional multichannel approaches (5.1, 7.1, etc) assume that there are loudspeakers in fixed positions, and all the recording, production and exhibition methods are based on this assumption. In contrast, Ambisonics does not depend on a fixed distribution of loudspeakers.
• Not necessarily object-based, even if it is layout independent. First order Ambisonics has 4 fixed channels. This is in contrast to other techniques such as VBAP or Wave Field Synthesis, which depend on an object-based method: every audio object is characterized by a mono track and a set of metadata indicating the location and other properties. While Ambisonics can be adapted to an object-based representation, this is not necessary. The fact that Ambisonics has a fixed number of channels it is important to save memory and processing requirements with hundreds or thousands of audio objects, as it is the case in complicated movie productions.
Ambisonics Flow Scheme
As a first step in the Ambisonics chain, a sound field needs to be encoded (ie, created synthetically from a mono recording) or recorded (using a special microphone).
X(t) = s(t) cos 𝟇 cos 𝞭
Y(t) = s(t) sin 𝟇 cos 𝞭
Z(t) = s(t) sin 𝞭
s(t) : arbitrary plain wave
𝟇 : azimuth
𝞭 : elevation
Recall that Ambisonics amounts to:
• An omnidirectional microphone for W(t).
• Three bidirectional (figure-8) microphones for X(t), Y(t) and Z(t).
All three microphones should be ideally coincident in one point of space. In practice, it is
difficult or impossible to set all three microphones in a single point. Instead, the ambisonic
microphone places four cardioid or subcardioid capsules in the vertices of a tetrahedron.
Taking in consideration that cardioid mic = (omni mic + figure-8 mic)/2, we can say:
W = FLU + FRD + BLD + BRU
X = FLU + FRD − BLD − BRU
Y = FLU − FRD + BLD − BRU
Z = FLU − FRD − BLD + BRU
• Linear transformations that do not depend on the spatial properties (for example, filtering and equalization): they can be done as usual, as long as they are applied equally to all channels
• Other spatial deformations, such as warping. For instance, one can create the effect of focusing on one direction of the sound field (dominance effect)
• Non-linear transformations, such as dynamic range control, are more difficult to handle and are currently a topic of research
The objective of the reproduction of Ambisonics is to be able to decode Ambisonics in a set of several loudspeakers distributed around the listener.
To infer these parameters two basic strategies can be adopted: basic reconstruction of the sound field, or psychoacoustic reconstruction.
We won’t get into details, now let’s try some practical exercises
Arteaga, Daniel. (2015). Introduction to Ambisonics.
presentation#1.pdf (130.0 KB)
#3 zoom link
#4 examples for ambisonics workflow
#5 For Next Session
Hey people, The idea would be for you to start putting some materials into a reaper session, as a first step to produce a spatial sound piece. You will share your own ideas and we will discuss as a group how to approach them. You don’t need to prepare a presentation, just try to have an idea of what would you like to do, and if for some reason you already have some sounds happening we could together.
Here you can find a video recording of our last session, is not edited, and we basically made a review of the 3 ambisonics packages showing some basic features with some pro and cons.
All this material is shared in the example link above.
unedited video first session
Here you can find a youtube channel with a lot of reaper tutorials.
You can send me a message trough here or telegram if you want to talk about your ideas.