beat bender

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As We proceed

• Beat Bender• Subsumption architecture• Prior Work• System Descriptions• Agents• Rules and Layers• Emergence • Aesthetics

Indian Institute of Information Technology

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About Beat Bender• BeatBender uses a behavior-based model to elicit emergent

rhythmic output from six autonomous agents

• From an artistic perspective, the rules used to define the agent behavior provide a simple but original composition language.

• From these simple rules emerge unexpected behavioral interactions that direct the formation of complex rhythmic output.


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Subsumption Architecture• The use of the subsumption architecture as a means of eliciting

emergent behavior was introduced by “Rodney Brooks “ in his seminal paper “Intelligence without Representation”.

• Avoids explicitly programmed procedural algorithms

• Subsumption architecture systems focus on developing sets of behaviors;

• These behaviors are implemented as layers, with some layers given priority over others


Layer 3

Layer 2

Layer 1

Layers Subsuming

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Applicability of SA• It was primarily used in the field of Robotics.

• Applicable to all the fields where an emergent behavior is expected.

• Bryson was first to propose the applicability of SA in the development of a musical component.


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Meta-creation and ALS started• Haile an anthromorphic Robotic Percussionist was

first artificial musical meta-creation.

• Kinetic Engine by Eigenfelt used network agent architecture to emulate percussive ensemble.

• Brown explored the rhythm generating potential of cellular automata (CA).

• Tokui and Iba demonstrate the use of interactive evolutionary computation as a means of producing rhythms in their CONGA system .


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Why Subsumption Architecture• CA as well as GA can also be applied.

• CA cells are processed in parallel

• Rules are hardcoded inhibiting responsive behavior.

• SA implicitly encode system behavior.

• It nullifies the complexity of GA.


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Basic Outline • Autonomous rhythmic sequencer utilizing a scalable multi-agent system.

• We shall proceed using six agents

• Each agent is responsible for the generation of one bit.

• Each Agent can be in two states, ON and OFF. Initially all of them are OFF.

• As the system starts each agent is activated using a set of rules.

• THESE RULES SUBSUME EACH OTHER


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Design Considerations• Beat bender project has got two distinct Phases.

• Building the architecture:-

Implementation of a robust tool that allows exploration of various layer rules

This becomes the behavioral basis for the agents.

It provides a flexible architecture for enabling and disabling the rules


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Design Considerations contd.

• Explore subsumption rules:-

Exploit subsumption layers and rules in order to elicit emergent behaviors.

This behaviors are evaluated based on the characteristics of the rythmic output.


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Beat Bender Agents

• They are capable of triggering ON and OFF audio events.

• The states are computed in parallel.

• SA determines which behavior to be performed based on the current.

• Once the new state has been set the system updates the Environment variables.

• If a particular agent’s state is set to ON then an audio event is triggered and one of three drum sounds plays.


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Pictorial representation


The state of all six agents over three time steps

The Layer Rules Interface tool

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Analysis Tools

• The BeatBender interface also consists of a graphical representation of the last six patterns played by the system

• The interface also captures each rhythm as a text file.


Particular agent state over time

One cycle of the systems state

ON

OFF

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Analysis Tools Continued

• The analysis tools were also essential for evaluating the output produced by the system.

• Each layer of the architecture must be implemented, tested, and modified in order to identify configurations that produce complex agent interactions, and consequently, interesting rhythmic output.

• For BeatBender layer tool allows for the exploration of the various permutations by providing a method for quickly reordering layer rules.


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System Components

• Agents

• System Goals

• Behaviors

• Perceptions

• Layers and rules


BUILDING BLOCKS

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Agents

• The agent Module acts as a container for the other components.

• Layer Module implements the whole SA.

• Sound Module implements the Audio playback system.

• Timing system is responsible for sequential activition of each agent.


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System Goals

• Rhythms produced should not be radically different from one time stamp to another.

• It should slowly evolve while maintaining some regularity.

• The rhythmic output must be aesthetic.

• Quality Criterion to evaluate musicality of each rhythm and its complexity.


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System Behaviors


• Firstly an Agent can change their state i.e. from ON to OFF or FLIP its state.

• Secondly the after processing, an agent is set to the ON state then it also must select a drum sound to use for playback.

• The current implementation of BeatBender provides three sound options, each one a different variation of a tabla drum: a long hit, a solid hit, and a low hit.

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Agent Perceptions


• Agent is continually updated with specific perceptions which are used to determine which behaviors are enacted under which conditions.

• Perceptions include the agent’s state, the previous agent’s state, the next agent’s state and the number of currently active agents in the system.

• Each one of these perceptions is used to determine which behavior should be enacted by the system.

• These conditional statements and the behaviors they enact are the basis for the subsumption layers that determine agent behavior.

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Layers and Rules• Layers are made up of rules . Each rule has an antecedent and a

consequence.

• Each layer is also given a rank rule.

• If the preconditions are met simultaneously only the rules associated with the highest ranked layer will have its behavior enacted.

• The rules in the beat bender can be divided into four categoris. Directed,Temporal,Collectiveand Undirected.


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Layers and Rules Contd.• Collective: If there are more than 3 active agents then turn this agent on IF TOTALAGENTS > 3 THEN ON• Directed: If the previous agent is on then flip this agent’s state. IF P = ON THEN FLIP• Temporal: If the agent has been on for the last four cycles then turn it off. IF CONSECUTIVE > 4 THEN OFF• Undirected: Rules are based on information about an agent and its

neighbors but without reference to a specific agent’s state.


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Evaluation• Beat bender is evaluated using two criteria :-

• Emergence: The emergence criterion was assessed using simple objective measures.

• Aesthetic: Assessed using subjective measures.


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Emergence• The application of individual rules does not produce interesting emergent

behavior

• Only though the interaction of two or more local elements is the process of convergence made visible.

• Individual rules do, however, produce rhythms that reveal two distinct types of behavior :-

Consistent behavior if each agent maintains the same state in every cycle.

Cyclical behavior if the agents’ states alternate on two or more subsequent cycles


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Individual RulesRule Applied Pattern Generated Behavior

IF P=OFF then ON X _ X _ X _ ConsistentIF N = OFF then ON X X X X X _ ConsistentIF P=N then FLIP X _ X _ X X

X X X X _ X_ X _ _ _ __ _ X _ X _X X _ _ _ _X X _ X _ _X X X X _ _

Cyclical

IF P = OFF then FLIP X _ X _ X _ _ X X_ _ X _ _ _ X _ _X _ X X _ X X _ __ X X X _ X _ _ __ X X _ X _ X X X_ _ X X X X _ X XX X X _ _ _ _ _ _

Cyclical


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Evaluation Example• An example of a pattern exhibiting this type of emergent behavior is generated

using the following set of rules.

• Rule 1: TURN ON AGENT• Rule 2: IF P = N then FLIP• Rule 3: 0 IGNORE, 1 ON, 2 IGNORE, 3 REST• Rule 4: IF STRIKES > 4 then OFF• Rule 5: IF ACTIVEAGENTS > 3 then FLIP

An audio sample of this rhythm can be heard at ww.aaronlevisohn.com/beatbender


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Rule Combinations• Using rules in combination with each other facilitates emergent agent

behaviors and the resulting complex rhythmic output.


#1:IF P = OFF thenON#2:IF N = OFF thenON

X X X X X _ Consistent

#1:IF P = OFF thenFLIP#2:IF N = OFF thenON

X X X _ _ _ X X X X X_ _ _ _ _ X X X X X _

Cyclical

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References• Aaron Levisohn and Philippe Pasquier,”BeatBender Subsumption Architecture

for Autonomous Rhythm Generation”.

• G. Weinberg and S. Driscoll, “Robot-human interaction with an anthropomorphic percussionist,”.

• A.R. Brown, “Exploring Rhythmic Automata,”Applications of Evolutionary Computing.

• http://www.aaronlevisohn.com/beatbender.html.


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Thanks for your patient hearing


beat bender

Documents

subsumption rules

agent behavior

simple rules

parallel rules

set of rules

system behavior

network agent architecture

emergent behaviors