dbx Pro AFS 224 User Manual

User Manual

Dual Channel Advanced Feedback Suppression Processor

®

AFS

™

224

WARNING FOR YOUR PROTECTION

READ THESE INSTRUCTIONS:

KEEP THESE INSTRUCTIONS

HEED ALL WARNINGS

FOLLOW ALL INSTRUCTIONS

DO NOT USE THIS APPARATUS NEAR WATER

CLEAN ONLY WITH A DRY CLOTH.

DO NOT BLOCK ANY OF THE VENTILATION OPENINGS. INSTALL IN ACCORDANCE WITH
THE MANUFACTURER’S INSTRUCTIONS.

DO NOT INSTALL NEAR ANY HEAT SOURCES SUCH AS RADIATORS, HEAT REGISTERS,
STOVES, OR OTHER APPARATUS (INCLUDING AMPLIFIERS) THAT PRODUCE HEA

T.

ONLY USE ATTACHMENTS/ACCESSORIES SPECIFIED BY THE MANUFACTURER.

UNPLUG THIS APPARATUS DURING LIGHTNING STORMS OR WHEN UNUSED FOR LONG
PERIODS OF TIME.

Do not defeat the safety purpose of the polarized or grounding-type plug. A polar­ized plug has two blades with one wider than the other. A grounding type plug has
two blades and a third grounding prong. The wide blade or third prong are pro­vided for your safety. If the provided plug does not fit your outlet, consult an elec­trician for replacement of the obsolete outlet.

Protect the power cord from being walked on or pinched particularly at plugs, con­venience receptacles, and the point where they exit from the apparatus.

Use only with the cart stand, tripod bracket, or table specified by the manufacture,
or sold with the apparatus. When a cart is used, use caution when moving the
cart/apparatus combination to avoid injury from tip-over.

Refer all servicing to to qualified service personnel. Servicing is required when
the apparatus has been damaged in any way, such as power-supply cord or plug is
damaged, liquid has been spilled or objects have fallen into the apparatus, the appa­ratus has been exposed to rain or moisture, does not operate normally, or has been
dropped.

POWER ON/OFF SWITCH: For products provided with a power switch, the power
switch DOES NOT break the connection from the mains.

MAINS DISCONNECT: The plug shall remain readily operable. For rack-mount or
installation where plug is not accessible, an all-pole mains switch with a contact
separation of at least 3 mm in each pole shall be incorporated into the electrical
installation of the rack or building.

FOR UNITS EQUIPPED WITH EXTERNALLY ACCESSIBLE FUSE RECEPTACLE: Replace fuse
with same type and rating only.

MULTIPLE-INPUT VOLTAGE: This equipment may require the use of a different line
cord, attachment plug, or both, depending on the available power source at instal­lation. Connect this equipment only to the power source indicated on the equipment
rear panel. To reduce the risk of fire or electric shock, refer servicing to qualified
service personnel or equivalent.

This Equipment is intended for rack mount use only.

SAFETY INSTRUCTIONS

NOTICE FOR CUSTOMERS IF YOUR UNIT IS EQUIPPED
WITH A POWER CORD.

WARNING: THIS APPLIANCE MUST BE EARTHED.

The cores in the mains lead are coloured in accordance with
the following code:

GREEN and YELLOW - Earth BLUE - Neutral BROWN - Live

As colours of the cores in the mains lead of this appliance may
not correspond with the coloured markings identifying the ter­minals in your plug, proceed as follows:

• The core which is coloured green and yellow must
be connected to the terminal in the plug marked
with the letter E, or with the earth symbol, or
coloured green, or green and yellow.

• The core which is coloured blue must be connect­ed to the terminal marked N or coloured black.

• The core which is coloured brown must be con­nected to the terminal marked L or coloured red.

This equipment may require the use of a different line cord,
attachment plug, or both, depending on the available power
source at installation. If the attachment plug needs to be
changed, refer servicing to qualified service personnel who
should refer to the table below. The green/yellow wire shall be
connected directly to the units chassis.

WARNING:If the ground is defeated, certain fault conditions in
the unit or in the system to which it is connected can result in
full line voltage between chassis and earth ground. Severe injury
or death can then result if the chassis and earth ground are
touched simultaneously.

The symbols shown above are internationally accepted
symbols that warn of potential hazards with electrical
products. The lightning flash with arrowpoint in an equi­lateral triangle means that there are dangerous voltages
present within the unit. The exclamation point in an equi­lateral triangle indicates that it is necessary for the user to
refer to the owner’s manual.

These symbols warn that there are no user serviceable
parts inside the unit. Do not open the unit. Do not
attempt to service the unit yourself. Refer all servicing to
qualified personnel. Opening the chassis for any reason
will void the manufacturer’s warranty. Do not get the unit
wet. If liquid is spilled on the unit, shut it off immediately
and take it to a dealer for service. Disconnect the unit
during storms to prevent damage.

IMPORTANT SAFETY INSTRUCTIONS

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

ATTENTION:
WARNING:

SHOCK DO NOT EXPOSE THIS EQUIPMENT TO RAIN OR MOISTURE

RISQUE DE CHOC ELECTRIQUE - NE PAS OUVRIR

TO REDUCE THE RISK OF FIRE OR ELECTRIC

CONDUCTOR

LIVE

L

NEUTRAL

N

E

EARTH GND

WIRE COLOR

Normal Alt

BROWN

BLUE

GREEN/YEL

BLACK

WHITE

GREEN

U.K. MAINS PLUG WARNING

A molded mains plug that has been cut off from the cord is unsafe.
Discard the mains plug at a suitable disposal facility. NEVER UNDER

ANY CIRCUMSTANCES SHOULD YOU INSERT A DAMAGED OR CUT
MAINS PLUG INTO A 13 AMP POWER SOCKET. Do not use the

mains plug without the fuse cover in place. Replacement fuse covers
can be obtained from your local retailer. Replacement fuses are 13
amps and MUST be ASTA approved

to BS1362.

IMPORTANT SAFETY INSTRUCTIONS

ELECTROMAGNETIC

COMPATIBILITY

This unit conforms to the Product
Specifications noted on the Declaration
of Conformity. Operation is subject to

the following two conditions:

• this device may not cause harmful

interference, and

• this device must accept any interfer-

ence received, including interference

that may cause undesired operation.

Operation of this unit within significant

electromagnetic fields should be avoided.

• use only shielded interconnecting

cables.

DECLARATION OF

CONFORMITY

Manufacturer’s Name: dbx Professional Products
Manufacturer’s Address: 8760 S. Sandy Parkway

Sandy, Utah 84070, USA

declares that the product:

Product name: dbx AFS 224
Note: Product name may be suffixed by the

letters-EU.

Product option: None

conforms to the following Product Specifications:

Safety: IEC 60065 (1998)

EMC: EN 55013 (1990)

EN 55020 (1991)

Supplementary Information:

The product herewith complies with the requirements of the Low
Voltage Directive 72/23/EEC and the EMC Directive 89/336/EEC as
amended by Directive 93/68/EEC.

Vice-President of Engineering
8760 S. Sandy Parkway
Sandy, Utah 84070, USA
Date: June 9, 2003

European Contact: Your local dbx Sales and Service Office or

Harman Music Group
8760 South Sandy Parkway
Sandy, Utah
84070 USA
Ph: [phone]
Fax: [phone]

Ta b le of Contents

AFS 224

Ta b le of Contents

Defining the AFS 224 ..............................................i

Service Contact Info ...............................................ii

Warranty..................................................................ii

Installation Recommendations...............................1

Basic Connections ..................................................1

Rear Panel Connections .........................................2

Front Panel Connections........................................2

User Setup...............................................................3

Applications ............................................................7

Block Diagram......................................................10

Specifications ........................................................11

AFS 224 User Manual

Table of Contents

®

AFS 224 Operation

AFS 224

®

Introduction

AFS 224 User Manual

i

AFS 224

Congratulations on your purchase of the dbx Professional Products AFS 224. The AFS 224
Advanced Feedback Suppression processor was designed to provide state-of-the-art feedback
elimination processing, while maintaining a simple and intuitive control interface. From the
powerful DSP module to the no-nonsense user interface, the AFS 224 provides all the process­ing and control necessary for both installation and live use. The AFS 224 is an absolute must
for any live sound application.

Ten and twelve filter feedback elimination processors have become the de facto standard, but
the engineering staff at dbx have never been content residing in the neighborhood of the sta­tus quo. So, to raise the bar once again, they went out and developed a dedicated feedback
suppression processor that offers up to 24 filters per channel with widths as narrow as 1/80 of
an octave. To achieve these staggering numbers dbx utilized their patent-pending AFS tech­nology that had previously only been available in the upper echelon line of products and made
it available in this stand-alone processor. In addition to the plethora of feedback suppression
filters available, the AFS 224 also offers selectable modes, live filter lift, and types of filtration,
which are all readily available via the intuitive user interface front panel. This manual will be
your guide to understanding the full functionality of the powerful AFS 224 series.

The dbx AFS 224 provide the user with the following features:

• dbx’s patent-pending Advanced Feedback Suppression (AFS™)

technology

• 24 Programmable Filters per Channel

• Stereo or Dual Independent Channel Processing

• Live and Fixed Filter Modes

• Selectable Filter Lift Times

• Application-specific filter types include:Speech; Music Low, Med and High

• Input Channel Metering

• 24 Segment Filter Metering per Channel

• XLR and TRS Electronically Balanced Input and Outputs

The AFS 224 Advantage

Key features that make the AFS 224 are its Fixed and Live modes of operation, as well as the
units Filter Lift capabilities. The Live Mode of operation continuously updates filter placement
which provides flexibility during a performance. The Filter Lift feature automatically removes
filter assignments that are no longer necessary, which in turn, maximizes sonic integrity.

The AFS 224 allows the user to optimize the elimination of feedback. In the past, graphic equal­izers were used to eliminate feedback from a system. This was an acceptable method for elim­inating feedback, but when this method was precision tested, the result clearly showed that a
single 1/3 octave EQ slider was removing approximately half of the signal power. With the AFS,
the unit removes the feedback automatically and the proprietary, precision AFS filters remove
only a fraction of the frequency spectrum. The diagram on the following page shows AFS as
opposed to competitive feedback eliminators and conventional graphic EQs:

Defining the AFS 224

INTRODUCTION

®

Introduction

AFS 224

AFS 224 User Manual

For more information regarding dbx Advanced Feedback Suppression (AFS™) technology,
please refer to the white paper section online at: www.dbxpro.com.

If you require technical support, contact dbx Customer Service. Be prepared to accurately
describe the problem. Know the serial number of your unit - this is printed on a sticker attached
to the rear or side of the unit. If you have not already taken the time to fill out your warranty
registration card and send it in, please do so now.

Before you return a product to the factory for service, we recommend you refer to the manu­al. Make sure you have correctly followed installation steps and operation procedures. If you
are still unable to solve a problem, contact our Customer Service Department at [phone]
for consultation. If you need to return a product to the factory for service, you MUST contact
Customer Service to obtain a Return Authorization Number.

No returned products will be accepted at the factory without a Return Authorization Number.

Please refer to the Warranty information on the following page, which extends to the first end­user. After expiration of the warranty, a reasonable charge will be made for parts, labor, and
packing if you choose to use the factory service facility. In all cases, you are responsible for
transportation charges to the factory. dbx will pay return shipping if the unit is still under war­ranty.

Use the original packing material if it is available. Mark the package with the name of the ship­per and with these words in red: DELICATE INSTRUMENT, FRAGILE! Insure the package prop­erly. Ship prepaid, not collect. Do not ship parcel post.

This warranty is valid only for the original purchaser and only in the United States.

1. The warranty registration card that accompanies this product must be mailed within 30 days
after purchase date to validate this warranty. Proof-of-purchase is considered to be the bur­den of the consumer.

2. dbx warrants this product, when bought and used solely within the U.S., to be free from
defects in materials and workmanship under normal use and service.

3. dbx liability under this warranty is limited to repairing or, at our discretion, replacing defec­tive materials that show evidence of defect, provided the product is returned to dbx WITH
RETURN AUTHORIZATION from the factory, where all parts and labor will be covered up to

Warranty

Service Contact Info

ii

Competitor’s
Feedback
Elimination

1/3 Octave EQ

dbx AFS™

®

Installation / Connections

AFS 224 User Manual

1

AFS 224

a period of two years. A Return Authorization number must be obtained from dbx by telephone.
The company shall not be liable for any consequential damage as a result of the product's use
in any circuit or assembly.

4. dbx reserves the right to make changes in design or make additions to or improvements upon
this product without incurring any obligation to install the same additions or improvements
on products previously manufactured.

5. The foregoing is in lieu of all other warranties, expressed or implied, and dbx neither assumes

nor authorizes any person to assume on its behalf any obligation or liability in connection
with the sale of this product. In no event shall dbx or its dealers be liable for special or con­sequential damages or from any delay in the performance of this warranty due to causes
beyond their control.

FOR RACK MOUNT USE ONLY - Install the AFS 224 in your rack with the provided rack
screws. When installed in a rack, the unit should be positioned with enough room (at least one
1U above the and 1U below the unit) to allow proper ventilation. The AFS 224 should not be
mounted above or below anything that generates excessive heat. Ambient temperatures should
not exceed 113

0

F (450C) when equipment is in use. Although the unit is shielded against radio
frequency and electromagnetic interference, extremely high fields of RF and EMI should be
avoided where possible.

The AFS 224 has balanced inputs and outputs that can be used with any balanced or unbal­anced line-level device.

To connect the AFS 224 to your sound system refer to the following steps:

• Turn off all equipment before making connections.

• Mount AFS 224 in a standard-width rack.

Install the AFS 224 in a rack with the rack screws provided. It can be mounted above or
below anything that does not generate excessive heat. Ambient temperatures should not
exceed 113° F (45°C) when equipment is in use. Although the unit’s chassis is shielded
against radio frequency and electromagnetic interference, extremely high fields of RF and
EMI should be avoided.

• Make audio connections via XLR, or 1/4” TRS jacks connectors according to application

needs. Both types of connectors for the inputs and outputs can be used for balanced or
unbalanced connections. The use of more than one connector at a time for the inputs could
unbalance balanced lines, cause phase cancellation, short a conductor to ground, or cause
damage to other equipment connected to the AFS 224. More than one output may be used
simultaneously as long as the combined parallel load is greater than 600Ω.

• Apply power to the AFS 224. Connect the AC power cord to the AC power receptacle on the

back of the AFS 224. Route the AC power cord to a convenient power outlet away from audio
lines. The unit may be turned on and off from a master equipment power switch. Since the
AFS 224 consumes a relatively small amount of power, the units may be left on continuously.

Basic Connection of the AFS 224

Installation Recommendations

Operation

®

Rear and Front Panels

Operation

AFS 224

AFS 224 User Manual

2

AFS 224 Rear

Power Cord Receptacle: Connects AC power to the AFS 224.

Input Connectors: Two types of input connectors are provided for input connections:

female locking XLR type connectors, and 1/4” tip-ring-sleeve phone jack connectors. The
maximum input level that the processor can accept is +20dBu (ref: 0.775Vrms).

Operating Level Switch: This button allows you to select between either +4dBu or

-10dBV nominal operating level.

Output Connectors: Two types of output connectors are provided for output connec­tions: male XLR type connectors, and 1/4” tip-ring-sleeve phone jack connectors.

AFS 224 Front

Input Level Bar Graph: These four LEDs indicate input level of the AFS 224. Input level

LEDs range from -10 to +18dBu.

I

MPORTANT - For maximum performance and proper operation, the average input sig-

nal should consistently light the 0 dBu LED, with the +10 dBu LED occasionally lighting.

Clip LED: This LED indicates that there is signal clipping at the input.

Bypass: This button bypasses the notch filters in the signal path by pressing once. Pressing

and holding the Bypass button is used to reset the filters. For more information regarding
filter reset, please see the Clearing Filters in the User Setup Section.

Type: This button is used to select the AFS type and to link Channel A and Channel B.
The AFS 224 offers several feedback suppression types, which are Speech, Music Low,
Music Medium and Music High. Each selected Type controls the width of the notch
filter used to remove the feedback. MUSIC HIGH

uses very narrow notch filters minimiz­ing the effect on the music, whereas the SPEECH type uses much wider notch filters allow­ing the AFS 224 to work faster. The Type, LED color and Frequency Q are listed below
and a representative filter Q graph is shown on the next page.

T

ype LED Q

Music High: Red 1/80th Octave
Music Med: Yellow 1/20th Octave
Music Low: Green 1/10th Octave
Speech: Not Lit 1/5th Octave

Front Panel

Rear Panel

®

User Setup

AFS 224 User Manual

3

Operation

AFS 224

Live Filter Lift: Live Filter Lift provides maximum sonic integrity by removing unnecessary
feedback filters. This button is used to select the live filter lift times and are indicated as follows:

LED

Lift Time

Not Lit - Lift Off
Green - 10 Seconds
Yellow - 10 Minutes
Red - 60 Minutes

Mode: This button is used to select FIXED (button is green) or LIVE (button is red). The Mode
button is also used to set the number of filters. For more information please see Section B Set
Up

AFS Filter LEDs: The AFS 224 offers 24 filter LEDs per channel, which are used to indicate the
number of fixed and set filters within each channel.

This section of the manual is provided to give the user step-by-step instructions for setting up
and optimizing the performance of the AFS 224.

A - Setting Gain Structure

The four basic ways to hookup the AFS 224 to your system are as follows:

1) Connected to the insert jack(s) on a microphone channel of a mixer.

2) Connected to the insert jack(s) on the main outputs of a mixer.

3) Connected to the subgroup insert jack(s) of a mixer.

4) Connected inline w/outputs of a mixer (output of mixer to input of 224, output of 224 to amplifiers).

For maximum performance and proper operation, the average input signal should consistently
light the 0 dBu LED, with the +10 dBu LED occasionally lighting. Hookup methods 1, 2 & 3
above are the preferred way to connect the AFS 224 since the insert points on most mixers are
pre output fader. This allows the proper signal level to be fed to the AFS 224 without the chan­nel or output fader affecting the level as the fader is moved up or down. Be sure to check the
mixer’s manual for the nominal operating point for the insert jacks, and then select the +4dBu
or -10dBV switch on the back of the AFS 224 accordingly.

User Setup

+3

+2

+1

-0

-1

-2

d

-3

B
u

-4

-5

-6

-7

-8

-9
700 1.2k750 820 850 900 .95k 1k

AFS 224 Filter Q's

Music High - 1/80th Octave

Mus ic Med - 1/20th Octave

Music Low - 1/10th Octave

Speech - 1/5th Octave

Hz

+3

+2

+1

-0

-1

-2
d

-3

B
u

-4

-5

-6

-7

-8

-9

®

If no insert points are available, then method 4 would be utilized. In this situation, be sure
that the AFS 224 input level allows the 0 and +10 dBu LEDS to light as indicated above. The
input level to the amplifiers may have to be reduced in this situation so that they are not over­driven by the signal from the AFS 224.

B – Setup Mode

The AFS 224 setup mode is used to set the Total Number of Filters and the Number of Fixed Filters
in each channel. The number of Live filters is the difference between the Total Number of Filters
and the Number of Fixed filters (Live filters = Total Filters-Fixed filters). Note: If channels are
linked (See F-2 Linking Channels) the setup will assign the same number of filters to channel 1
and 2.

B-1 Entering Setup Mode

Press and hold the channel 1 <MODE> button until the Filter LED's light from left to right
and repeat. Release the channel 1 <MODE> button to enter the Setup Mode. This is indi­cated by the <MODE> button lighting yellow. You are now in the Set Total Number of Filters
mode.

B-2 Selecting the Total Number of Filters

The Set Total Number of Filters mode is indicated by the channel <MODE> button lighting
yellow when in the Setup mode. The current setting for the Total Number of Filters is indi­cated by the number of Filter LED's lit for that channel. To change the Total Number of Filters
use the channel <LIVE FILTER LIFT> button to increment and the <TYPE> button to decre-
ment the number of filters. Each press of the button will increment or decrement the Total
Number of Filters. Press and hold each button to slowly increment or decrement the num­ber.

W

arning: Changing the Total Number of Filters may remove feedback filters already set.

B-3 Selecting the Number of Fixed Filters

Use the selected channel <MODE> button to toggle to the Set Number of Fixed Filters mode
indicated by the selected channel’s <MODE> button, which will light green. The current set­ting for the Number of Fixed Filters is indicated by the number of Filter LED's lit for that chan­nel. To change the number of Fixed Filters, use the selected channel’s <LIVE FILTER LIFT>
button to increment and the <TYPE> button to decrement the number of filters. Each press
of the button will increment or decrement the Total Number of Fixed Filters. Press and hold
each button to slowly increment or decrement the number. Pressing the selected channel ‘s
<MODE> button will toggle between the Set Total Number of Filters and the Set Number of
Fixed Filters mode for each channel. If the channels of the AFS 224 are linked (see F-2
Linking Channels) the above procedure will set the same number of filters for both channels.

W

arning: Changing the Number of Fixed Filters may remove feedback filters already set.

B-4 Exit Setup Mode

To exit the setup mode and return to operation mode press and hold the channel 1 <MODE>
button until the Filter LED's light from left to right and repeat (same as entering Setup mode).

C - Using Fixed mode

The AFS 224 offers two main modes of operation, Fixed and Live. Fixed mode is used to detect
and remove feedback problems in the system due to microphone placement, room modes etc.
Once set these filters are not removed until reset or cleared. Live mode detects and removes
feedback during a performance or event.

User Setup

Operation

AFS 224

AFS 224 User Manual

4

®

User Setup

3AFS 224 User Manual

5

Operation

AFS 224

C-1 Ringing out a system

Fixed mode filters are set before a performance in a process called "ringing out a system".
This is done after all other system EQ'ing has been done. First, bring down the main mix,
turn off all music sources and open all the mics. Place the AFS 224 into fixed mode by
pressing the <MODE> button for the channel. A <MODE> button lighting green indicates
Fixed mode for that channel. Select the channel’s filter type by pressing the channel’s
<TYPE> button. See Using Types in Fixed mode below. Slowly turn up the main mix,
raising the gain of the system, until feedback occurs. The AFS 224 will detect and remove
feedback by placing notch filters at the feedback frequency. Continue to slowly raise the
gain until all feedback has been eliminated or all fixed filters have been used, this will be
indicated by the flashing <MODE> button.

C-2 Using Types in Fixed mode

The AFS 224 offers several feedback suppression types. These are Speech, Music Low,
Music Medium and Music High. The selected type controls the width of the notch filter
used to remove the feedback. Music High uses very narrow notch filters minimizing the
effect on the music. The Speech type uses much wider notch filters allowing the AFS 224
to work faster. See Type in Front Panel section for descriptions and indicators.

During the filter setting process the filter type can be changed by pressing the channels
<TYPE> button. This will change the filter type for the next filter and will not change exist­ing filters. When all fixed filters have been used new feedback occurrences will not be
removed. Pressing the <MODE> button will place the AFS 224 into Live mode (indicated
by the <MODE> button lit Red) and feedback will continue to be removed. If more fixed
filters are needed, reallocate more filters by following the steps in Setup Mode or clear the
filters (See section E-Clearing Filters) by pressing and holding the <BYPASS> button until
all the Filter LED's blink and repeat the procedure above with a wider filter type.

D - Using Live Mode

Live Mode allows feedback filters to be set and removed based on changes in the environment
and is designed to be used during a performance. The AFS 224 can be put into Live Mode by
pressing the <MODE> button until it lights red. Once in Live Mode, if feedback occurs a fil­ter will be set at the feedback frequency. If there are additional occurrences of feedback, addi­tional notch filters will be set until all the Live Filters are used. If new frequencies begin to fee
back and no more Live Filters are available, the AFS algorithm will take the first Live Filter set,
and move it to the new feedback frequency. The AFS 224 will continue to “round robin”
through the Live Filters as new feedback is detected.

AFS 224 Filter Q's

+3

+2

+1

-0

-1

-2

d

-3

B
u

-4

-5

-6

-7

-8

-9
700 1.2k750 820 850 900 .95k 1k

Music High - 1/80th Octave

Mus ic Med - 1/20th Octave

Music Low - 1/10th Octave

Speech - 1/5th Octave

Hz

+3

+2

+1

-0

-1

-2
d

-3

B
u

-4

-5

-6

-7

-8

-9

®

User Setup

Operation

AFS 224

AFS 224 User Manual

6

D-1 Using Live Filter Lift

Live Filter Lift provides maximum sonic integrity by removing unnecessary feedback filters.
The Live Filter Lift function provides a timer for each of the Live Filters. This timer length can
be adjusted by pressing the <LIVE FILTER LIFT> button, and can be switched between off,
1 minute, 10 minutes or 60 minutes. The filter lift default time is 10 minutes from the facto­ry. If Live Filter Lift is on, once a filter’s time period has expired, the AFS algorithm will check
to see if the feedback filter is still necessary. If no longer needed, the notch filter will then
slowly lift. If the filter is still required to eliminate feedback, the timer will be reset. If the
Live Filter Lift is off, the notch filters will remain in place until they are cleared, or until need­ed for other frequencies.

D-2 Using Types in Live Mode

As in Fixed Mode, the AFS 224 offers several feedback suppression types. These types con­trol the width of the notch filter used to remove the feedback. The Speech type uses wider
notch filters allowing the AFS 224 to work faster. The Music types provide sharper notch fil­ters than the Speech type, with up to 1/80th of an octave in the Music High type (see AFS fil­ter Q graph on the previous page). Pressing the <TYPE> button switches between the dif-
ferent types. You can select different types for both Live and Fixed Mode.

E - Clearing Filters (Fixed and Live)

To clear the Live filters, press and hold the <BYPASS> button on the selected channel for approx-
imately two seconds. The currently assigned live filter LEDs will flash. If you wish to clear only
the Live filters, release <BYPASS> button at this time. If you wish to reset all filters, continue to
hold the <BYPASS> button an additional two seconds until all filter LEDs are flashing. At this
point, release the <BYPASS> button and all filters will be cleared.

F - Other Functions

The AFS 224 also offers the security feature of front panel lockout and the ability to link channels.
The following information provides instruction for both procedures.

F- 1 Front Panel Lockout
To lockout all access to the front panel of the AFS 224, press and hold the channel 1 <LIVE
FILTER LIFT> button until all of the filter LEDs light from outside to inside. To unlock the

front panel lockout, press and hold the channel 1 <LIVE FILTER LIFT> button until the LEDs
light from the inside to the outside.

F-2 Linking Channels

To link both channels, press and hold the Channel 1 <TYPE> button until all button LED’s
blink will set the unit into LINKED mode. As feedback in either channel occurs, notch filters
will be placed in both channels to remove feedback. To unlink channels, press and hold the
channel 1 <TYPE> button. After the unit is unlinked, both channels will behave indepen­dently.

®

Application Guide

Application 1 - Insert On the Microphone Channel

This application is ideal for dedicated feedback suppression on microphone channels of a mix­ing console. This application provides the user with individual channels of 24 filter of feed­back suppression per microphone.

1. Connect the channel insert output from the mixer to the input of the AFS 224.

2. Connect the output of the AFS 224 to the insert return of the mixer.

For maximum performance and proper operation, the input signal to the dbx 224 must cause
the “0” dBu LED to light fairly consistently and the “+10” dBu LED to light occasionally. Be
sure to check the mixer’s manual of the nominal operating point for the insert jacks, and then
select the +4dBu or -10dBV switch on the back of the 224 accordingly.

Applications

7

Operation

AFS 224

AFS 224 User Manual

Microphone In

Input
Channel 1
AFS 224

2468

2468

2468

0

46

2

0

-10+1

-2

-3

-4

-5

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

Aux 1

Aux 2

Pan

0

0

10

10

Aux 1

46

2

2

8

8

0

0

10

10

Aux 2

-10+1

-2

-2

+2

+2

+3

-3

+3

-3

+4

-4

+4

-4

-5

-5

+5

+5

Pan

Mute

Mute

L / R

L / R

+10

+10

+5

+5

0

0

-5

-5

-10

-10

-20

-20

-30

-30

-∞

-∞

1234

Aux 1

46

Aux 2

-10+1

Pan

10

8

10

+2

+3

+4

+5

2468

0

Aux 1

46

2

0

Aux 2

-10+1

-2

-3

-4

-5

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

10

8

10

+2

+3

+4

+5

2468

0

Aux 1

46

2

0

Aux 2

-10+1

-2

-3

-4

-5

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

10

10

+5

5

Channel 2

AFS 224

2468

0

Aux 1

46

2

8

0

Aux 2

-10+1

-2

+2

+3

-3

+4

-4

-5

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

6

Input

2468

10

2

8

10

+2

+3

-3

+4

-4

+5

+10

+5

0

-5

-10

-20

-30

-∞

0

0

-10+1

-2

-5

Mute

L / R

Aux 1

46

Aux 2

Pan

7

10

8

10

+2

+3

+4

+5

2468

0

Aux 1

46

2

0

Aux 2

-10+1

-2

-3

-4

-5

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

8

2468

10

0

Aux 1

46

2

8

10

0

Aux 2

-10+1

-2

+2

+3

-3

+4

-4

-5

+5

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

Output A Output B

10

8

10

+2

+3

+4

+5

+10

+5

-10

-20

-30

-∞

2468

0

Aux 1

46

2

0

Aux 2

-10+1

-2

-3

-4

-5

Pan

Mute

L / R

0

-5

Microphone In

10

8

10

+2

+3

+4

+5

®

Application 2 - Insert On the Main Stereo Outputs of a Mixing Console

This application is ideal for dedicated feedback suppression on the outputs of a mixing con­sole. This application provides the user with dual channels of 24 filters of feedback suppres­sion per channel.

1. Connect the stereo output inserts of the mixer to the inputs of the AFS 224.

2. Connect the outputs of the AFS 224 to the insert returns of the console.

3. Apply power to the mixer and amplifiers.

For maximum performance and proper operation, the input signal to the dbx 224 must cause
the “0” dBu LED to light fairly consistently and the “+10” dBu LED to light occasionally. Hookup
at the insertion point since the insert points on most mixers are pre output fader. This allows
the proper signal level to be fed to the 224 without the channel or output fader affecting the
level as the fader is moved up or down. Be sure to check the mixer’s manual for the nominal
operating point for the insert jacks, and then select the +4dBu or -10dBV switch on the back of
the 224 accordingly.

Application Guide

Operation

AFS 224

8

AFS 224 User Manual

2468

0

2468

0

-2

-3

-4

-5

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

-10+1

Aux 1

Aux 2

0

0

10

10

Aux 1

2468

2468

0

0

10

10

Aux 2

-10+1

+2

-2

+2

-2

+3

-3

+3

-3

-4

-4

+4

+4

+5

-5

+5

-5

Pan

Pan

Mute

Mute

L / R

L / R

+10

+10

+5

+5

0

0

-5

-5

-10

-10

-20

-20

-30

-30

-∞

-∞

1234

2468

2468

-10+1

Output to SpeakerOutput to Speaker

-10+1

10

Aux 1

10

Aux 2

+2

+3

+4

+5

Pan

8

Mixer Output to Input
Channel 2
AFS 224

2468

2468

0

10

0

10

Aux 1

Aux 1

2468

2468

0

10

0

10

Aux 2

Aux 2

-10+1

-10+1

-2

+2

-2

+2

-3

+3

-3

-4

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

Output A Output B

+3

-4

+4

+4

-5

+5

-5

+5

Pan

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

To Pow er Amp

Insert

Returns

Mixer Output to Input

Channel 1

AFS 224

2468

2468

2468

2468

2468

0

10

Aux 1

Aux 1

2468

0

10

Aux 2

Aux 2

-10+1

+2

-2

+3

-3

-4

+4

+5

-5

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

0

0

10

10

Aux 1

Aux 1

2468

2468

0

0

10

10

Aux 2

Aux 2

-10+1

-10+1

+2

-2

+2

-2

+3

-3

+3

-3

-4

-4

+4

+4

+5

-5

+5

-5

Pan

Pan

Pan

Mute

Mute

L / R

L / R

+10

+10

+5

+5

0

0

-5

-5

-10

-10

-20

-20

-30

-30

-∞

-∞

5

0

0

10

10

Aux 1

2468

2468

0

0

10

10

Aux 2

-10+1

+2

-2

+2

-2

+3

-3

+3

-3

-4

-4

+4

+4

+5

-5

+5

-5

Pan

Mute

Mute

L / R

L / R

+10

+10

+5

+5

0

0

-5

-5

-10

-10

-20

-20

-30

-30

-∞

-∞

6

7

®

Applications Guide

386 User Manual

9

Operation

AFS 224

Application 3 - Insert on the Subgroups of a Mixer

This setup is ideal for applications that require feedback suppression on certain instruments
such as microphones, while keeping instrument that desire feedback (such as guitars) separat­ed. This application provides the user with dual channels of 24 filter suppression per stereo
channel of the mixing console subgroup.

1. Connect the stereo output inserts of the mixer to the inputs of the AFS 224.

2. Connect the outputs of the AFS 224 to the insert returns of the console.

3. Making sure that all outputs are muted, apply power to the mixer and amplifiers.

For maximum performance and proper operation, the input signal to the dbx 224 must cause
the “0” dBu LED to light fairly consistently and the “+10” dBu LED to light occasionally. Be sure
to check the mixer’s manual for the nominal operating point for the insert jacks, and then select
the +4dBu or -10dBV switch on the back of the 224 accordingly.

AFS 224 User Manual

Microphone In

2468

0

Aux 1

2468

0

Aux 2

-10+1

-2

-3

-4

-5

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

1234

10

10

+2

+3

+4

+5

+10

+5

-10

-20

-30

-∞

2468

0

2468

0

-10+1

-2

-3

-4

-5

Mute

L / R

0

-5

Microphone In

2468

0

10

Aux 1

Aux 1

2468

0

10

Aux 2

Aux 2

-10+1

+2

-2

+3

-3

-4

+4

+5

-5

Pan

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

10

10

+2

+3

+4

+5

2468

0

2468

0

-10+1

-2

-3

-4

-5

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

10

10

+2

+3

+4

+5

Pan

+10

8

Subgroup Input
Channel 2
AFS 224

2468

2468

0

-10+1

10

10

Aux 1

Aux 1

2468

0

10

10

Aux 2

Aux 2

-10+1

+2

-2

+2

+3

-3

+3

-4

+4

+4

+5

-5

+5

Pan

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

0

2468

0

-2

-3

-4

-5

Mute

L / R

+5

0

-5

-10

-20

-30

-∞

Output A Output B

Insert

Returns

Subgroup Input

Channel 1

AFS 224

2468

2468

2468

2468

0

0

10

10

Aux 1

Aux 1

Aux 1

Aux 2

Pan

10

+2

+3

+4

+5

+10

2468

0

Aux 2

-10+1

-2

-3

-4

-5

Pan

Mute

L / R

+5

0

-5

-10

-20

-30

-∞

5

10

+2

+3

+4

+5

2468

0

Aux 2

-10+1

-2

-3

-4

-5

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

Pan

6

10

10

+2

+3

+4

+5

+10

0

Aux 1

2468

0

Aux 2

-10+1

-2

-3

-4

-5

Pan

Mute

L / R

+5

0

-5

-10

-20

-30

-∞

7

10

10

+2

+3

+4

+5

0

Aux 1

2468

0

Aux 2

-10+1

-2

-3

-4

-5

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

®

Application 4- Connected Inline with the Outputs of a Mixer

This application is ideal for dedicated feedback suppression on the outputs of a mixing con­sole. This application provides the user with dual channels of 24 filters of feedback suppres­sion per output channel of the mixing console.

1. Connect the outputs from the mixer to the inputs of the AFS 224.

2. Connect the outputs of the AFS 224 to the power amps.

3. Apply power to the mixer and amplifiers.

For maximum performance and proper operation, the input signal to the dbx 224 must cause
the “0” dBu LED to light fairly consistently and the “+10” dBu LED to light occasionally.

The input level to the amplifiers may have to be reduced in this situation so that they are not
overdriven by the signal from the 224.

Applications Guide

Operation

AFS 224

10

AFS 224 User Manual

Output to Speaker

Output to Power Amp Output to Power Amp

Mixer Output to Input

46

46

46

2

0

Aux 1

46

2

0

Aux 2

-10+1

-2

-3

-4

-5

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

1234

2

2

8

8

0

0

10

10

Aux 1

46

46

2

2

8

8

0

0

10

10

Aux 2

-10+1

-10+1

+2

-2

+2

-2

+3

-3

+3

-3

-4

-4

+4

+4

+5

-5

+5

-5

Pan

Mute

Mute

L / R

L / R

+10

+10

+5

+5

0

0

-5

-5

-10

-10

-20

-20

-30

-30

-∞

-∞

10

Aux 1

10

Aux 2

+2

+3

+4

+5

Pan

Channel 1

AFS 224

46

2

8

8

0

10

Aux 1

46

2

8

8

0

10

Aux 2

-10+1

-2

+2

-3

+3

-4

+4

-5

+5

Pan

Mute

L / R

+10

+10

+5

+5

0

-5

-10

-10

-20

-20

-30

-30

-∞

-∞

2

0

2

0

-2

-3

-4

-5

Mute

L / R

0

-5

46

Aux 1

46

Aux 2

-10+1

Pan

5

Output to Speaker

Mixer Output to Input
Channel 2
AFS 224

46

46

46

2

8

0

10

Aux 1

46

2

8

0

10

Aux 2

-10+1

+2

-2

+3

-3

-4

+4

+5

-5

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

6

2

2

8

0

10

Aux 1

46

2

8

0

10

Aux 2

-10+1

+2

-2

+3

-3

-4

+4

+5

-5

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

8

8

0

10

10

Aux 1

46

2

8

8

0

10

10

Aux 2

-10+1

+2

-2

+2

+3

-3

+3

-4

+4

+4

+5

-5

+5

Pan

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

7

8

46

46

2

2

2

-3

-4

Mute

+10

+5

0

-5

-10

-20

-30

-∞

0

Aux 1

46

0

Aux 2

-10+1

-2

-5

L / R

8

8

0

10

10

Aux 1

46

2

8

8

0

10

10

Aux 2

-10+1

+2

-2

+2

+3

-3

+3

-4

+4

+4

+5

-5

+5

Pan

Pan

Mute

L / R

+10

+5

0

-5

-10

-20

-30

-∞

Output A Output B

®

Block Diagram

386 User Manual

11

Operation

AFS 224

Block diagram

AFS 224 User Manual

OutputsInputs

AFS 224

RF

Filter

Block Diagram

D/A

Filter meter LEDs

Bypass

Type

Mode

Live Filter Lift

Input meter

Input

DSP

A/D

TYPE IV™

RF Filter

Micro

Processor

CLIP Detect

Bypass

Logic

Programmable

Type

Mode

Live Filter Lift

®

Analog Inputs:

Number of Inputs: 2

Connectors: Female XLR and 1/4” TRS

Type: Electronically balanced/unbalanced, RF filtered

Impedance: Balanced 50kΩ, Unbalanced 25kΩ

Max input line level: +20dBu

CMRR: >40dB, typically >55dB @ 1kHz

Analog Outputs:

Number of Outputs: 2

Connectors: Male XLR and 1/4” TRS

Type: Electronically balanced/unbalanced, RF filtered

Impedance: Balanced >120Ω, unbalanced >60Ω

Max Output Level: +20dBu

A/D Performance:

Type: dbx Type IV™ conversion system

Dynamic Range: >113 dB A-weighted, >110 dB unweighted, 22kHz BW

Type IV™ dynamic range: >119 dB, A-weighted, 22kHz BW

>117 dB, unweighted, 22kHz BW

A/D Conversion: 24 bit

D/A Performance:

Dynamic Range: 112 dB A-weighted, 109dB unweighted

D/A Conversion: 24 bit

System Performance:

Sample Rate: 48kHz

Dynamic Range: >109dB A-weighted, >106 dB unweighted, 22kHz BW

THD+N: 0.003% typical at +4dBu, 1kHz

Frequency Response: 20Hz – 20kHz, +/- 0.5dB

Interchannel Crosstalk: >80dB typical

Crosstalk input to output: >80dB typical

Operating Voltage: 100VAC 50/60Hz, 120VAC 60Hz and 230VAC 50/60Hz

Power Consumption: 9 Watts

Safety Agency Approvals: UL 6500, IEC 60065, EN 55013, E 60065

Specifications

Specifications

Operation

AFS 224

12

AFS 224 User Manual

®

®

8760 South Sandy Pkwy.

Sandy, Utah 84070

Phone: [phone]

Fax: [phone]

Questions or comments

E•mail us at: [e-mail]

or visit our World Wide Web home page at:

www.dbxpro.com

18-6398-A

A Harman International Company