Transcript Automatic Equalization for Live Venue Sound Systems

Automatic Equalization for
Live Venue Sound Systems
Damien Dooley, Final Year ECE
Initial Presentation, Tuesday 2nd October 2007
Contents
• Background
• Project Description
• Initial Work (Room Acoustic Modeling)
Background
• In live venues it can be quite challenging to get a balanced sound
• Several factors can influence a significant deviation between the
desired output and the actual output of the system.
• Factors include, room dimensions, room structure, number of
people in the room, furniture, sound source and listener location.
The Project
• This project aims to create a tool that will help automate the
process of achieving a balanced sound.
• This will be achieved by developing a DSP system which will
acoustically model the environment in which the PA system is
setup.
• This system will compensate for the specific properties of the
room to ensure that the perfect sound is achieved in each
venue.
The system will consist of a
microphone which will record the
sound at a particular location in
the room.
A pre-determined sound
sequence will be played through
the PA and the DSP system will
record the audio signal received.
The system will then estimate
the impulse response of the
system which will be a
combination of the input signal
and the room acoustics.
The Project
•
•
•
•
Capture audio signals using MATLAB
Develop and implement filters on the audio
Create a simple acoustic model in SIMULINK, (more on this…)
Develop an adaptive filter that can adapt to the acoustic
properties of the room, again thru SIMULINK
• Create an active DSP system which will adjust the
discrepancies in the audio in real time (adaptive filtering)
Initial Work
Room Acoustic Modeling
• In order to properly understand how to implement this design,
one must understand how sound behaves in various rooms.
This is known as room acoustic modeling.
When a sound is generated
in a room the listener will
first hear the sound via the
direct path to the source.
The listener will then hear
the reflections in the sound
and the magnitude will
decrease exponentially after
each echo.
Room Acoustic Modeling
• Sabine’s equation for reverberation time
• RT = 0.161V/A
• This equation yields the time it takes (in seconds) for the sound
of the room to decay by 60dB.
• V = Volume of the room
• A = Absorption Window
(A is calculated by taking the total surface area of the room and
multiplying it by it’s absorption coefficient.)
Room Acoustic Modeling
Some absorption coefficients are laid out as follows
Material
Concrete Block Unpainted
Concrete Block Painted
Glass, Window
Plaster On Lath
Plywood Panelling
Carpet On Pad
Gypsum Board
Drapery, Lightweight
125
0.36
0.1
0.35
0.14
0.28
0.08
0.29
0.03
250
0.44
0.05
0.25
0.1
0.22
0.24
0.1
0.04
Frequency (Hz)
500
1000
0.31
0.29
0.06
0.07
0.18
0.12
0.06
0.05
0.17
0.09
0.57
0.69
0.05
0.04
0.11
0.17
2000
0.39
0.09
0.07
0.04
0.1
0.71
0.07
0.24
4000
0.25
0.08
0.04
0.03
0.11
0.73
0.09
0.35
Example
Taking a concrete room painted, with
no furniture, pip at 500Hz.
2
V = 2 X 5 X 10 = 100m3
A = (Surface Area) x (Absorption
Coefficient)
5
A = {2(50) + 2(20) + 2(10)} X {0.06}
A = 9.6
10
RT = 0.161V/A
RT = 0.161(100)/9.6 = 1.677s
Hence, it takes 1.677 seconds for the pip at 500Hz to drop by 60dB.
Summary
• The project will require a deeper understanding about how
sound behaves in different environments.
• It will greatly increase my knowledge of MATLAB and
SIMULINK, and the general area of DSP.
Questions?