This presentation is based on the Audio and Video subjectm, and in this presentation explained in brief of Public Address System.

1. Public Address
System
PREPARED BY:
MAULIK SANCHELA (14EC38)
E. C. DEPT.
RAJKOT
Subject: Audio & Video System

2. ALWAYS TURN DOWN VOLUME BEFORE CONNECTING AUDIO EQUIPMENT.
FAILURE TO DO SO MAY RESULT IN PAINFUL FEEDBACK WHICH MAY DAMAGE
HEARING AND EQUIPMENT
THERE ARE MANY ELECTRONIC FACTORS THAT MAY AFFECT HOW
WORKS. NOT ALL EQUIPMENT IS COMPATIBLE. MISUSE MAY LEAD TO
EQUIPMENT AND/OR HEARING DAMAGE.
AUDIO EQUIPMENT CAN BE DELICATE AND EXPENSIVE. PLEASE HANDLE
CARE, AND IF YOU ARE NOT SURE OF SOMETHING, ASK.
CAUTION

3. BASIC TERMS (grossly simplified)
Signal - The electrical current produced by a device.
Input - 1: The place where a signal enters a piece of equipment; 2: The signal entering
a piece of equipment.
Output - 1: The place where a signal exits a piece of equipment; 2: The signal exiting a
piece of equipment.
Trim/Gain - Typically the amount a signal is amplified relative to its original intensity
expressed in Decibels (dB). The Mackie uses the term “trim,” but many companies and
texts use the term “gain.” They are interchangeable for our purposes. I will use trim in
this manual since that is what is printed on our console.
Fader - A slider that adjusts the signal intensity (volume).
Unity - A setting where the input voltage or intensity equals the output voltage or
intensity.
FOH - Front-of-house; areas in front of the stage, including the control booth,
catwalks, audience seating area, lobby, etc.
Snake - An audio cable consisting of multiple individual lines.

4. SIGNAL CHAIN: HOW DO WE MAKE IT WORK?
In sound reinforcement, the signal chain is made up of the parts of the
sound system a signal must go through in order to be heard clearly by an
audience. In it’s simplest form it is made up of 4 basic steps:

5. The origin of the signal. This could be a microphone, CD player,
computer, iPod, electric guitar, record player (what’s that?), cassette
deck, electronic keyboard, etc.
There are typically 2 types of signal sources categorized by the
strength of their output signals.
Mic level, as its name suggests, is typical for microphones. It is very
low voltage, around 2 millivolts (mV), or thousandths of a volt.
Line level, typically from most other sources, is a stronger, though
widely variable signal, typically from 77.5 mV to 24.5 volts
SOURCE

6. Where the source signal is received, modified, and directed to the
desired output(s). The mixer is the primary tool here. This step may also
include effects processors, equalization, and a variety of other signal
modifications.
Distribution & Control:

7. Amplification
The boosting of the signal to a speaker level strength, 24.5 volts or higher,
that can drive a speaker.
Output
In a word, speakers. Output could also end up on tape, CD, or other medium,
but our context, speakers is the most relevant.
Happily, for the purposes of this manual, the final 2 steps
are not anything you will have to work with.

8. The process of setting up an audio system is
merely connecting the links in the chain.

9. Power Phantom
Power for
condenser
mics
Channel Inputs 1
through 20 Your
source devices plug
in here. (mics, CDs,
FOH snake, etc.)
Only 16 and 17 are
pictured. Inputs 21-
24 are stereo inputs
that will be covered
in book 2 – Line
Level Devices.
WHAT’S IMPORTANT ON THE BACK OF THE CONSOLE?
Mono Main Out to
amplifiers. Must be
connected to work!
DO NOT ADJUST
OUTPUT LEVEL!

10. Trim/Gain
control —
adjusts
incoming signal
strength
WHAT’S IMPORTANT ON THE FRONT OF THE CONSOLE?
Power Light
Signal Meters
Main (L/R)
Fader —acts as
master volume
control for all
faders
Mute — turns off the
channel input signal
(on/off switch).
Output assignment
— directs the signal
to an output (in this
case the Main (L-R)
fader ).
Channel fader —
adjusts output level
(volume) of channel
signal.

11. ON THE MAIN SOUND RACK IN THE CONTROL BOOTH
TURN THE SYSTEM ON
Push “SYSTEM
POWER” switch should be
lit on main audio rack in
control booth.
Main sound rack – control booth

12. Push “System Mode” switch
so “Manual” indicator light is
lit.
Main sound rack – control booth
System Mode switch
Manual mode indicator
SET THE SYSTEM MODE TO
“MANUAL”

13. IF YOU ARE USING THE MAIN SEATING AREA ONLY, NOT
THE TURNTABLES:
Push “TURNTABLE CONTROL”
buttons so the “LOCAL” indicator
lights are lit.

14. Make sure all faders and Trim
settings are all the way down!!
(see pictures)
If something is accidentally turned
up the following step can create
horrendous noise and potentially
damage equipment.
TURN ON POWER (SEE PG. 6
FOR SWITCH LOCATION)
MAKING IT WORK
STEP 1: POWER ON & PRESET

15. Plug input device (source) into
desired channel on the back of the
mixer.
MAKING IT WORK
STEP 2: PATCH
Note: If you have several devices, it
pays to plan out the channels ahead
of time to make operation logical.
Line level inputs here. (CD, DVD, PC,
MP3, etc.)
Line level devices generally have 1/4
inch phone plugs on them (example to
right).
Mic level inputs here. (microphones,
wireless receivers, etc.) Mic level
devices generally have XLR connectors
on them.
XLR cable
FOH snake

16. MAKING IT WORK
STEP 3: OUTPUT ASSIGNMENT
Assign channel to desired output by
pushing in the appropriate button (in
most cases this will be “L-R”)

17. MAKING IT WORK
STEP 4: SET FOR UNITY
Set MAIN FADER to “U” (unity gain)
IF you are setting a mic level input-
set channel fader at “U”
IF you are setting a line level input
(for example, a CD player) - play device and
fade up to “U”; less if it gets too loud before
Unity.

18. MAKING IT WORK
STEP 5: SET TRIM LEVELS
IF you are setting a mic level input –
As someone is speaking into the mic,
GRADUALY turn up the trim until you hear a
ringing from the speakers. This is the
beginning of “feedback”. Back off the trim so
that a loud noise into the mic (cough, clap, or
“Pow!”) will not cause painful feedback.
IF you are setting a line level input
(for example, a CD player) –
Turn up the trim until you reach the desired
volume.
You may not need any trim boost at all. For
some recordings or devices you may not
even get to set the fader as high as Unity. For
other recordings, such as a poorly recorded
cassette or a computer with the audio output
turned low, you may need to set the trim
quite high.
Note: The gain on the right is
extraordinarily high for our theatre.

19. IT ISN’T WORKING! NOW
WHAT?
DON’T PANIC; TROUBLESHOOT!

20.  The following suggestions include the problems you are most likely to
encounter, and the questions you should ask when trying to isolate a
problem.
 If you think you have done all of the previous steps correctly, your first step
should be to CHECK AGAIN! Most of the time it is operator error. Don’t
worry, it happens to everyone...frequently
TROUBLESHOOTING
CAUTION
TAKE THE CHANNEL FADER DOWN BEFORE PLUGGING,
UNPLUGGING, UNMUTING, OR SWITCHING ASSIGNMENTS ON
AND OFF. YOU MAY SUDDENLY FIX THE PROBLEM ONLY TO
DEAFEN EVERYONE AROUND WITH FEEDBACK.

21. IF YOU ARE WORKING AT THE MIXER
ASK THE FOLLOWING QUESTIONS
IS THERE SIGNAL
GETTING TO THE
CONSOLE FROM
THE SOURCE?
Check the input signal light with the trim
up.
The green light above the “Mute” button
should blink if there is reasonable signal
level coming in. Turn up the trim gradually
to check.
If YES (the light is
blinking), the
problem is in the
booth. Check the
easy stuff first
Are your outputs assigned to L-R?
Is the main fader up?
Are you bringing up the correct channel
fader?
Is the channel muted?

22. IF YOU ANSWERED “YES” TO THE PREVIOUS
QUESTIONS, YOU’LL HAVE TO CHECK THE
MORE BASIC STUFF
IS THE SYSTEM TURNED ON AT THE MAIN RACK?
IS THE SYSTEM SET TO “MANUAL” MODE?
IS THE “MAIN OUT” ON THE SNAKE PLUGGED INTO THE
“MONO OUT” ON THE CONSOLE?
DID THE CONSOLE OUTPUT LEVEL GET TURNED DOWN?

23. IF YOU ARE NOT GETTING SIGNAL TO THE
CONSOLE, (THE GREEN LIGHT WON’T BLINK)…
ARE YOU ADJUSTING THE TRIM ON THE CORRECT
CHANNEL?
DID YOU PATCH THE CORRECT SNAKE INPUT?
DID YOU PATCH INTO THE CORRECT CHANNEL?
IF YOU ARE USING A CONDENSER MIC, IS PHANTOM
POWER ON?

24. IF THINGS ARE STILL NOT WORKING, THE
PROBLEM IS MOST LIKELY BETWEEN THE
SOURCE AND THE CONSOLE
IS THE SOURCE
PLUGGED INTO THE
CORRECT INPUT?
Confirm the input # the source is plugged
into matches the input # going into the
channel. For example, you were told to plug
the mic into input 1, but plugged into input
2 by accident.
IS THE CABLE BAD? Try the device with a different cable
IS THE INPUT BAD?
Try the device and original cable in a
different input (making the necessary
change at the console, of course!)