PRO DSP1100P

Users Manual Bedienungsanleitung

Version 1.0 October 1998

FEEDBACKDESTROYER

www.behringer.de

EG-Declaration of Conformity
Spezielle Studiotechnik GmbH
acc. to the Directives 89/336/EWG and 73/23/EWG
We, BEHRINGER INTERNATIONAL GmbH Hanns-Martin-Schleyer-Strae 4 D - 47877 Willich
Name and address of the manufacturer or the introducer of the product on the market who is established in the EC
herewith take the sole responsibility to confirm that the product: FEEDBACKDESTROYERPRO DSP1100P
Type designation and, if applicable, Article-No
which refers to this declaration, is in accordance with the following standards or standardized documents:
x EN 60065 x EN 55020 x EN 55013
x EN 61000-3-2 x EN 61000-3-3 x EN 55022
The following operation conditions and installation arrangements have to be presumed: acc. to Operating Manual

B. Nier, President

Name, address, date and legally binding signature of the person responsible

Willich, 01.10.1998

SAFETY INSTRUCTIONS
CAUTION: To reduce the risk of electrical shock, do not remove the cover (or back). No user serviceable parts inside; refer servicing to qualified personnel.
WARNING: To reduce the risk of fire or electrical shock, do not expose this appliance to rain or moisture. This symbol, wherever it appears, alerts you to the presence of uninsulated dangerous voltage inside the enclosure - voltage that may be sufficient to constitute a risk of shock. This symbol, wherever it appears, alerts you to important operating and maintenance instructions in the accompanying literature. Read the manual.
DETAILED SAFETY INSTRUCTIONS: All the safety and operation instructions should be read before the appliance is operated. Retain Instructions: The safety and operating instructions should be retained for future reference. Heed Warnings: All warnings on the appliance and in the operating instructions should be adhered to. Follow instructions: All operation and user instructions should be followed. Water and Moisture: The appliance should not be used near water (e.g. near a bathtub, washbowl, kitchen sink, laundry tub, in a wet basement, or near a swimming pool etc.). Ventilation: The appliance should be situated so that its location or position does not interfere with its proper ventilation. For example, the appliance should not be situated on a bed, sofa rug, or similar surface that may block the ventilation openings, or placed in a built-in installation, such as a bookcase or cabinet that may impede the flow of air through the ventilation openings. Heat: The appliance should be situated away from heat sources such as radiators, heat registers, stoves, or other appliance (including amplifiers) that produce heat. Power Source: The appliance should be connected to a power supply only of the type described in the operating instructions or as marked on the appliance. Grounding or Polarization: Precautions should be taken so that the grounding or polarization means of an appliance is not defeated. Power-Cord Protection: Power supply cords should be routed so that they are not likely to be walked on or pinched by items placed upon or against them, paying particular attention to cords and plugs, convenience receptacles and the point where they exit from the appliance. Cleaning: The appliance should be cleaned only as recommended by the manufacturer. Non-use Periods: The power cord of the appliance should be unplugged from the outlet when left unused for a long period of time. Object and Liquid Entry: Care should be taken so that objects do not fall and liquids are not spilled into the enclosure through openings. Damage Requiring Service: The appliance should be serviced by qualified service personnel when: - The power supply cord or the plug has been damaged; or - Objects have fallen, or liquid has been spilled into the appliance; or - The appliance has been exposed to rain; or - The appliance does not appear to operate normally or exhibits a marked change in performance; or - The appliance has been dropped, or the enclosure damaged. Servicing: The user should not attempt to service the appliance beyond that is described in the Operating Instructions. All other servicing should be referred to qualified service personnel.

FEEDBACKDESTROYERPRO

Ultra-high performance 2-channel digital Feedback Destroyer / Parametric EQ powered by a 24-bit high-speed DSP
s 20-bit A/D and D/A converters with 64/128 times oversampling for ultra-high headroom and resolution s Automatically and intelligently searches out and destroys up to 12 frequencies per channel s 24 fully programmable Parametric Filters that can be set manually or via MIDI
s Set-and-forget default setting enables immediate and super-easy Feedback Destroyer performance
s Single-Shot mode automatically searches and destroys feedback and locks the filter until you reset them manually s Auto mode continuously monitors the mix, resetting programmed filters automatically
s Manual mode allows for setting up to 2 x 12 fully parametric filters including Frequency, Bandwidth and Gain s Single-Shot, Auto and Manual modes are assignable for each filter
s Free FEEDBACK DESTROYER software allows for total remote control via PC (download at www.behringer.de) s Two software engines give you independent or coupled functions on left and right channels s Internal 24-bit processing with professional 46kHz sampling rate
s Servo-balanced Inputs and Outputs on gold-plated XLR and TRS Jack connectors for high signal integrity s Full MIDI capability and user preset memories to store programs for instant recall
s Accurate eight-segment LED level meters simplify level setting for optimum performance s Future-proof software-upgradeable architecture
s High-quality components and exceptionally rugged construction ensures long life and durability s Internal power supply design for professional applications s Manufactured under the ISO9000 management system 4

DSP1100P

FOREWORD
Dear Customer, Welcome to the team of FEEDBACKDESTROYERPRO users and thank you very much for expressing your confidence in BEHRINGER products by purchasing this unit. It is one of my most pleasant tasks to write this letter to you, because it is the culmination of many months of hard work delivered by our engineering team to reach a very ambitious goal: making an outstanding device better still. The FEEDBACKDESTROYERhas for some time been a standard tool used by numerous studios and P.A. rental companies. The task to improve one of our best-selling products certainly meant a great deal of responsibility, which we assumed by focusing on you, the discerning user and musician. It also meant a lot of work and night shifts to accomplish this goal. But it was fun, too. Developing a product usually brings a lot of people together, and what a great feeling it is when everybody who participated in such a project can be proud of what weve achieved. It is our philosophy to share our joy with you, because you are the most important member of the BEHRINGER family. With your highly competent suggestions for new products youve greatly contributed to shaping our company and making it successful. In return, we guarantee you uncompromising quality (manufactured under ISO9000 certified management system) as well as excellent technical and audio properties at an extremely favorable price. All of this will enable you to fully unfold your creativity without being hampered by budget constraints. We are often asked how we can make it to produce such high-grade devices at such unbelievably low prices. The answer is quite simple: its you, our customers! Many satisfied customers means large sales volumes enabling us to get better conditions of purchase for components, etc. Isnt it only fair to pass this benefit back to you? Because we know that your success is our success, too! I would like to thank all people whose help on Project FEEDBACKDESTROYERPRO has made it all possible. Everybody has made very personal contributions, starting from the designers of the unit via the many staff members in our company to you, the user of BEHRINGER products.

The BEHRINGER FEEDBACKDESTROYERPRO fits into one standard 19" rack unit of space (1 3/4"). Please allow at least an additional 4" depth for the connectors on the back panel. Be sure that there is enough space around the unit for cooling and please do not place the FEEDBACKDESTROYERPRO on high temperature devices such as power amplifiers etc. to avoid overheating.
Before you connect your FEEDBACKDESTROYERPRO to the mains, please make sure that your local voltage matches the voltage required by the unit! (see chapter 5 for details)
The mains connection of the FEEDBACKDESTROYERPRO is made by using a mains cable and a standard IEC receptacle. It meets all of the international safety certification requirements. Please make sure that all units have a proper ground connection. Please ensure that only qualified persons install and operate the FEEDBACKDESTROYERPRO. During installation and operation the user must have sufficient electrical contact to earth. 1. INTRODUCTION 7
Electrostatic charges might affect the operation of the FEEDBACKDESTROYERPRO! For further information on correct installation see chapter 5 Installation. As a standard the audio inputs and outputs on the BEHRINGER FEEDBACKDESTROYERPRO are fully balanced. If possible, connect the unit to other devices in a balanced configuration to allow for maximum interference immunity. The automatic servo function detects unbalanced connections and compensates the level difference automatically (6dB correction). The MIDI links (IN/OUT/THRU) are made over standardized DIN patch cords. The data communication is isolated from ground by opto couplers.

1.3 Hook up & go

We know you are anxious to get to work with your new FEEDBACKDESTROYERPRO, the band is probably setting up now, youre half an hour behind schedule, it is hectic, dark and damp. If you promise to read the whole manual tomorrow, or at least next week, we show you how to get up and go and get through this night alive. If youve used a variety of PA gear, youll have the FEEDBACK DESTROYERPRO up and running after quickly perusing the manual. If youre not so experienced, dont worry, it will come to you. In both cases, still read the manual! The following may then help you get it happening with a minimum of fuss.

1. 2. 3.

In order to use the full potential of your FEEDBACKDESTROYERPRO, please bear in mind the following points: No device will fully compensate for wrong microphone handling! Be aware that there are some actions on stage may still result in feedback. Allow some time for experimentation you may need to get used to the DSP1100P over several gigs. The FEEDBACK DESTROYERPROs single shot filters are well suited to automatically attenuate resonances which are most likely to cause feedbacks.

2.4 Working with programs
In order to store your favorite settings, the FEEDBACK DESTROYER PRO has ten user presets and a default preset. All operating parameters can be stored, i.e. your programs are recalled in full detail. Owing to state-ofthe-art circuitry, no internal battery is needed, hence the memory contents will not be lost. In the default preset (display --), which serves as a basis for creating your own programs, all filters remain in the parametric mode, with bandwidth set to 1 octave, a frequency of 500Hz and 0dB gain. 2.4.1 Recalling programs After power-up, the FEEDBACK DESTROYER PROs display reads the number of the preset last used. The jog wheel allows you to conveniently select the preset of your choice. Turn the rotary control to the left to step through the programs in descending order. Turn it to the right to increment the programs. The default preset is located in front of the first program.
Please note that the FEEDBACK DESTROYER PRO generally activates the newly selected presets 2. OPERATION
only after about one second, which is indicated by a dot in the lower right corner of the display. After loading the data, the FEEDBACK DESTROYER PRO enables the preset and the dot disappears. This brief interruption avoids the direct activation of every preset, as you scroll through the preset list with the jog wheel. Thus, the FEEDBACK DESTROYER PRO makes sure that no "unwanted" programs are loaded unintentionally. Additionally, you can rotate the jog wheel at high speed and still have the time to specifically select the preset of your choice, instead of any of its "neighbors". 2.4.2 Choice of mode Each filter mode has two letters assigned to it, who appears in the display after pressing the FILTER MODE key. The following display messages can be recognized:
Display Mode of operation OF PA AU SI LO Off Parametric EQ Auto Single Shot Locked (S)
Tab. 2.1: FEEDBACK DESTROYER PRO operating modes To change the filter mode, you first have to press the FILTERSELECT key to specify the number of the filter (1 to 12) with the jog wheel. Using the ENGINE keys you can not only select the left or right channel, but also both ones at the same time. Then you can choose the filter mode by simply pressing the FILTER MODE key and turning the jog wheel. The display message L (locked) informs you that a filter from the Single-Shot mode is already suppressing a feedback. You can unlock such a filter by switching it back to single mode. As soon as a new feedback will be found, the FEEDBACK DESTROYER PRO switches the filter from the old frequency to the new one. If you leave the Auto or Single-Shot mode and enter the Parametric mode, the filter keeps all parameter settings. In order to avoid an inadvertent change, the filter mode selection takes place after a period of approximately one second. This is indicated by a dot in the lower right corner of the display. By pressing and keeping the FILTER MODE and the GAIN key for about 2 seconds you can adjust the feedback threshold within a range of -3dB to -9dB. 2.4.3 Editing filter parameters To change filter settings, the filter has to situate in Parametric EQ mode. In this case you can adapt the center frequency by pressing the FREQUENCY key. Depending on the frequency, either the Hz or kHz indicator to the right of the display lights up. If you want to lift the frequency to e.g. 2700Hz turn the jog wheel until the ISO frequency (2.5kHz, see table 6.1 standard ISO frequencies) closest to this value appears in the display and the kHz indicator lights up. The FINE key allows you to fine tune the chosen standard ISO frequency within a tuning range of 1/3 octave (in 1/60-octave steps). The mathematical proportion between the displayed value and the absolute frequency, and an easy guide to quickly find the desired frequency is available in chapter 7 (frequency chart). The bandwidth of the filter can be adjusted by selecting the BANDWIDTH key. The adjustable bandwidth ranges from 2 octaves down to 1/60 octave. By pressing the GAIN key it is possible to set the desired boost or cut of the selected frequency. A + signals that the level is being increased and a - signals a decreasement. In Single-Shot and Auto mode it is not possible to change the filter parameters. In these modes you only are allowed to call up the parameters. However you can convert such a filter into a parametric one with same frequency, and bandwidth, but with a gain of 0dB. You simply have to press and keep the FILTER MODE key for about 2 seconds. To reactivate a locked filter simply choose the Single-Shot or Auto mode.

2.4.4 Storing programs Use the STORE key to store the program. Basically, all parameter changes in Parametric EQ mode can be saved. Filters working in Single-Shot or Auto mode will adjust and store the required parameters automatically. Example: s You recall a program for editing. Then you edit the preset as desired using the function keys and the jog wheel. During this process, the flashing STORE key reminds you that the preset settings have been changed but not saved yet. Press the STORE key once. The display reads the current preset number and starts flashing. To keep the original preset, use the jog wheel to select a different preset that can be overwritten. Press the STORE key again to save the edits to the selected preset. If you wish to overwrite the original preset, simply press the STORE key twice (after editing) to save all changes you have made.
Whenever you have edited a preset and pressed the STORE key twice, all previous settings in this preset are erased and overwritten with the new parameter values. However, if you wish to keep the original preset, use the jog wheel to select another preset before you press the STORE key a second time.

2.5 MIDI control

Use the MIDI key combination to select the MIDI parameters you wish to adjust. For this purpose press and keep the IN/OUT and the STORE keys for about two seconds. All parameters can be edited with the jog wheel and the IN/OUT key. The MIDI menu includes six pages which you can select by pressing the IN/OUT key (forwards) and the STORE key (backwards) several times. On the first page you can select the MIDI channel. The display reads a small c (= channel). The jog wheel adjusts a channel from 1 through 16. To switch off the MIDI function simply select the 0 value (displayed as -). On the second page you can select MIDI Omni mode, i.e. the unit transmits/receives on all 16 MIDI channels. The display reads O (=Omni). Use the jog wheel to activate (1) or deactivate (0) Omni mode. The third page allows for configuring controller commands. On its right-hand side, the display reads a capital C (=Controller). The jog wheel selects one of the following four controller modes:
Displa y 4 Mode No controller data are transmitted Controller data are received but not transmitted Controller data are transmitted but not received Controller data are transmitted and received As 3, with additionally the automatic filter parameters
Tab. 2.2: Controller settings
When you choose value 4 the FEEDBACK DESTROYER PRO will also send the settings of the automatic filters.

The fourth page gives you access to the program change setup. The display reads a capital P (=Program). Here, too, four modes can be selected with the jog wheel, as follows:
Display Mode No program change data are transmitted Program change data are received but not transmitted Program change data are transmitted but not received Program change data are transmitted and received
Tab. 2.3: Program change settings The fifth page of the MIDI menu shows the store enable flag represented by a capital S in the display. The value 0 disables the reception of controller #18, and therefore protects the user presets from being modified 14 2. OPERATION
via MIDI. Accordingly, the value 1 enables MIDI controller #18 so that you can modify or replace presets with a remote MIDI device or a sequencer. In this case the actual settings will be stored directly to the location that corresponds to the controller value.
Attention! Since the store enable mode allows you to access memory locations directly via MIDI, it is possible that stored presets will be replaced or altered if controller #18 messages are sent on the same MIDI channel. The purpose of this mode is to facilitate MIDI backup and restore operations without express confirmation at the FEEDBACK DESTROYER PRO. It is therefore recommended to disable (flag=0) this mode as soon as the intended data transfer has ended. This is done automatically when you switch off the FEEDBACK DESTROYER PRO.
On the sixth, and presently the last, page you can access the System Exclusive functions. This is indicated by a d (for dump) in the display. To the left of this d a number is displayed: - 0 means that no SYSEX data will be sent or accepted. - 1 will enable the FEEDBACKDESTROYERPRO to receive data. When STORE is pressed the unit will wait for data, this is shown by flashing dots (LEDs) in the display. The MIDI button LED flashes signaling that SYSEX data is being received. - 2 will enable the FEEDBACKDESTROYERPRO to send a bulk dump. Start your sequencer and press STORE on the unit to start the transmission. If you press the IN/OUT key again on the fifth page, the FEEDBACKDESTROYERPRO quits MIDI setup mode. To load these settings again, select 1, press STORE and start your sequencer. If you press IN/OUT again, you will leave the MIDI setup. You can at all times press any other key to leave the MIDI setup directly. During a bulk dump all audio functions of the FEEDBACK DESTROYER PRO will be deactivated. The full-featured MIDI implementation of the FEEDBACK DESTROYER PRO allows for easily integrating the FEEDBACK DESTROYER PRO into any MIDI system. s MIDI IN Any MIDI data sent to the FEEDBACK DESTROYER PRO (sequencer, MIDI footswitch, etc.) are received via the MIDI IN jack. For example, if you wish to use the FEEDBACK DESTROYER PRO as an effects device for your guitar rack, you can connect the MIDI IN jack to a MIDI footswitch that allows for selecting program presets. If your rack includes another MIDI effects device (e.g. a multi-effects processor), the data sent from the MIDI footswitch can be routed via the FEEDBACK DESTROYER PROs MIDI THRU jack to your multieffects processor. s MIDI THRU The MIDI THRU jack is used to loop through incoming MIDI data, i.e. any control data received at the MIDI IN of the FEEDBACK DESTROYER PRO will be transmitted via the MIDI THRU jack to other MIDI devices/ instruments. s MIDI OUT The MIDI OUT jack allows for transmitting MIDI data that originate from the FEEDBACK DESTROYER PRO. We are currently developing a software editor which will allow for storing single items of the FEEDBACKDESTROYER PRO`s internal data on an external medium. Thus, it will be possible to archive FEEDBACKDESTROYERPRO settings and presets on a computer, sequencer or MIDI data recorder. Both MIDI Control Change and MIDI Program Change commands will be transmitted when you edit or recall filter settings. Detailed information on this future software editor are available from our BEHRINGER hotline (tel.+49(0)2154-920666), our international distributors and/or our Internet homepage http://www.behringer.de.

situations. Before applying the FEEDBACK DESTROYER PRO, it is therefore advisable to remove the condition causing the feedback problems. For example, try different microphone positions! Use the FEEDBACKDESTROYERPRO in the monitor path and in single channels with critical signals. If there is no other way to eliminate feedback, you can insert the FEEDBACK DESTROYER PRO into the main mix bus. Unless your mixing console has dedicated insert points for the main mix bus, you can simply connect the FEEDBACK DESTROYER PRO between mixing console and power amp. If required, adapt the levels with the Operating Level switch. Wire the unit as shown below:
Fig. 3.2: Using the FEEDBACK DESTROYER PRO in the main mix bus
3.4 Using the FEEDBACK DESTROYER PRO in single channels and sub-groups

Channel Insert

Sub-Group Insert
Fig. 3.3: Inserting the FEEDBACK DESTROYER PRO in single channels and sub-groups If you want to make sure that deliberately produced feedback signals, such as guitar feedback, are not eliminated, you should try inserting one or several FEEDBACK DESTROYER PRO`s into single channels (e.g. vocal mics) which are susceptible to feedback. Or, you could use the sub-groups of your mixing console by routing any channels susceptible to feedback (e.g. all vocal mics) to one or several sub-groups. Thus, all less critical signals (e.g. line signals, lower-level instrumental microphones) can pass through the mixing console unaltered, while only the critical microphone channels are monitored from the FEEDBACKDESTROYERPRO. In this way, you can protect your P.A. system against feedback and still use wanted feedback signals.
3.5 Using the FEEDBACK DESTROYER PRO in a studio environment
With its highly flexible configuration the FEEDBACK DESTROYER PRO also delivers good results in a professional studio or home recording environment, as it provides a maximum of twelve fully parametric equalizers per channel in Parametric EQ mode. Thus, you can realize any application ranging from slight processing to the total manipulation of music signals. For example, you can use the FEEDBACK DESTROYER PRO as an equalizer for your studio monitors or to enhance the EQs in your mixing console, as these are often only semiparametric.

4. TECHNICAL BACKGROUND

The steady development of modern sound reinforcement systems has made it possible to produce almost any level of loudness. Yet, the increase in loudness goes in line with a need for optimized audio quality. Today, audiences expect to hear a powerful and transparent sound. Nothing can spoil a live event more than interference and feedback. High volume levels and the use of ever sophisticated monitor systems with a great number of speaker boxes have increased the potential risk of feedback loops. Up to now sound engineers have used conventional 1/3octave equalizers to suppress unwanted feedback. Now, the BEHRINGER FEEDBACK DESTROYER PRO gives you the option to delegate this task to the FEEDBACK DESTROYER PRO, so that you can pay your music your undivided attention instead of having to suppress feedback with graphic EQs using a trial-and-error approach. To fully understand how the BEHRINGER FEEDBACK DESTROYER PRO works you will need to know the meaning of a few fundamental terms used in signal equalization, such as: s dB, decibel s bandwidth / quality factor (Q) s octave, 1/3-octave With the FEEDBACK DESTROYER PRO, as with any other type of equalizer, the amount of boost/attenuation applied to a specific frequency is expressed in decibels (dB). Whats a decibel? The abbreviationdB is not a unit (although often used as one), but describes a logarithmic proportion. The entire dynamic range of human hearing (from the threshold of audibility to a jet-airplane, see fig. 4.1) starts with about 0.00002 Pa (threshold of audibility) and goes up to 113 Pa (threshold of pain). 4. TECHNICAL BACKGROUND 19
The range of sound pressure levels or the dynamic range of human hearing encompasses a factor of 10,000,000. This enormous range of values is difficult to handle and additionally does not represent the subjective perception of sound, since human hearing tends to use a logarithmic curve. When an increase in loudness by the factor two is perceived as one step, four times the loudness level equals two steps. So, the decibel is a unit of measurement that describes a level in relation to a reference quantity. To make clear which reference quantity is meant, the abbreviation SPL (sound pressure level) is sometimes used together withdB. Starting with a value of 0dB SPL (= 2*10-5 Pa) for the threshold of audibility, anydB values can be calculated by means of the following formula:

L = 20 log

L = e.g. the absolute sound pressure level indB SPL p1 = e.g. a reference sound pressure of 0.00002 Pa p2 = the sound pressure (in Pa) produced by the sound source to be calculated log = decimal logarithm.

Jet Engine

Threshold Of Pain
Sound-Pressure Level (dB SPL)

Power Drill

Machinery Hall "Loud" Office Normal Conversation Quiet Apartment Recording Studio

Falling Leaves

Threshold Of Audibility
Fig. 4.1: Dynamic range of human hearing As can be seen, human hearing has a very wide dynamic range of about 130dB, which surpasses the range of a DAT or CD player with an approximate range of 96dB. From a physical point of view, a 3dB boost corresponds to an increase in power by the factor 2. However, the human ear perceives a signal to be twice as loud as before only if it is boosted by about 10dB. This will give you an idea of the range of boost or attenuation that can be realized with the 24 filters of the FEEDBACK DESTROYER PRO. For each filter, you can apply a boost of +16dB or a cut of -48dB, i.e. you can boost the selected frequency by the subjectively perceived factor 3 (physically 40) or attenuate it by the factor 27 (physically 60,000)! The sound which an EQ produces not only depends on the selected frequency and the amount of gain (expressed indB); the bandwidth of the filters also plays an important role. Here, we generally use the so-called absolute bandwidth of a filter, which is measured from the lower to the upper cutoff frequency. Starting from there, you can divide the absolute bandwidth by the filters center frequency to calculate the relative bandwidth. The quality factor (Q) is simply the reciprocal value of the relative bandwidth.
Filter attenuated by 8 dB at 1kHz 0 dB Bandwidth = 600 Hz -2 dB -3 dB -4 dB

Center frequency = 1 kHz

-10 dB
-12 dB 200 Hz 1 kHz 5 kHz
Fig. 4.2: Typical equalizer filter curve The filter bandwidth can also be expressed in octaves (as on the FEEDBACK DESTROYER PRO). The following table shows a list of decimal Q values vs. octaves:
Octave 1/6 1/4 1/3 1/2 3/3/3
Quality factor (Q) 8.65 5.76 4.32 2.87 1.90 1.41 0.92 0.67 0.40
Tab. 4.1: Octaves vs. Q factors Now the following relationship becomes clear: the higher the Q factor, the narrower the frequency band that can be cut or boosted. On the BEHRINGER FEEDBACK DESTROYER PRO you can adjust the relative bandwidth conveniently with the infinitely variable jog wheel. The filter bandwidth can be tuned from 2 octaves (120/60 octaves) down to 1/60 octave (for fine adjustments).

4.1 Feedback

Almost every concert goer may have experienced the howling and squealing of an improperly set sound reinforcement system. Feedback is one of the main problems encountered during live events. A feedback loop is produced when a microphone signal is reproduced by an amplifier system, to be picked up again (with the same phase) by the microphone. Thus, feedback is built up at all frequencies where the distance between microphone and speaker corresponds to a multiple of the signals wavelength.

Speaker Box

Microphone

Mixing Console

Power Amp
Fig. 4.3: Typical feedback loop Basically, any microphone signal passing through an amplifier is liable to generate feedback. Unfortunately, the feedback frequencies of P.A. systems differ, and even one single system can have varying feedback frequencies, as these depend largely on the room acoustics. Feedback can be caused by the following conditions: s The microphones are too close to the speaker boxes or the speakers are badly positioned (monitor system). s The microphone channels on the mixing console are not set up correctly. s The microphones used are not operated in accordance with their directivity (e.g. cardioid/super-cardioid). s The acoustic properties of the room are unfavorable. Tiled walls and floors heavily reflect the sound. All rooms feature a number of natural resonances sometimes with high quality factor. At such frequencies the potential risk of feedback is increased. In addition to the acoustic properties of the room, the relative position of the microphone with reference to the loudspeaker plays a decisive role for the generation of feedback. In practice, this phenomenon can be observed with microphone held directly in front of a speaker, thus producing feedback. Of course, the first thing to do in such a case is to move the microphone away from the speaker. When doing so, you can hear the feedback frequency change, because a variation in the distance between microphone and loudspeaker results in a variation of feedback frequencies. It is therefore very difficult to anticipate feedback frequencies and avoid their occurrence by means of equalizers with fixed settings.

4.2 Graphic equalizers

Graphic equalizers are part of the audio engineers standard equipment for live applications. In this context, graphic EQs usually perform three main tasks: s Fine tuning the mix to your taste and the style of music. s Fine tuning the mix to the room and speaker acoustics. s To some extent, audio engineers can use graphic EQs to manually suppress annoying feedback. The 1/3-octave design with 31 faders per channel has become the standard among graphic equalizers. Here, the spacing between individual filter frequencies is 1/3 octave. The quality factor (Q) of the filters (usually 1/3 octave) is fixed as are the frequencies controlled with the 31 filters. 1/3-octave equalizers are very popular (e.g. our ULTRA-CURVE PRO DSP8024) because they are so easy to operate. The fader positions clearly show how the signal is being processed, especially since graphic EQs have fixed frequencies based on the so-called ISO standard. So, all graphic equalizers designed to meet the ISO standard feature the same fixed frequencies. Once youve got used to work with a 1/3-octave equalizer, you will find the FEEDBACK DESTROYER PRO a highly convenient tool, as it splits up the audio spectrum into the ISO frequencies (see table 1.2), which enables you to access the most important frequencies quickly. 22 4. TECHNICAL BACKGROUND

Quantization Steps

U (Voltage)
-8 -7 -6 -5 -4 -3 --1 --7 -8 -3 -4 -5 -0101 0110

Continuous Analog Signal

t (Time)
Quantization Errors (Noise)

Digital Words

Conversation Rate
Fig. 4.4: Transfer diagram for an ideal linear ADC (2s complement representation) Digital distortion is quite different, as illustrated by this simplified example. If we take the situation where a 4 bit word has the positive maximum value of 0111, and add to it the smallest possible value of 0001 (in other words, the smallest increase in amplitude possible), the addition of the two results in 1000 - the value of the negative maximum. The value is turned on its head, going instantly from positive max to negative max, resulting in the very noticeable onset of extreme signal distortion.

5. INSTALLATION

5.1 Rack mounting
The BEHRINGER FEEDBACKDESTROYERPRO fits into one standard 19" rack unit of space (1 3/4"). Please allow at least an additional 4" depth for the connectors on the back panel. Be sure that there is enough air space around the unit for cooling and please do not place the FEEDBACKDESTROYERPRO on high temperature devices such as power amplifiers etc. to avoid overheating.

5.2 Mains connection

The mains connection of the FEEDBACKDESTROYERPRO is made by using a mains cable and a standard IEC receptacle. It meets all of the international safety certification requirements.
Please make sure that all units have a proper ground connection. For your own safety, do not remove the ground connection within the units or at the supply, or fail to make this connection at all.
Before you switch on the unit, check that it is configured to match your AC mains voltage requirements. If it
does not comply, then it is necessary to switch the operating voltage to the correct supply requirements BEFORE turning on the unit, otherwise the unit could be severely damaged. You will find this combined fuse holder/voltage selector at the back, adjacent to the IEC receptacle. IMPORTANT: This does not apply for general export models which are built for one operating voltage only. The AC voltage selection is defined by the position of the fuse holder. If you intend to change the operating voltage, remove the fuse holder and twist it by 180 degrees before you reinsert it. Matching the two markers monitors the selected voltage.

MIDI for Musical Instruments Digital Interface.
The MIDI connectors found on the rear panel are of the universally used 5 pin DIN type. You require suitable MIDI cables to connect the FEEDBACKDESTROYERPRO to other MIDI devices. Normally complete cables will be purchased for this use, you can of course make your own, using a high quality cable with two cores and shielding (like microphone cable), with as connectors two good 180 degree DIN plugs. Pin 2 (center) is connected to the cables shield, pins 4 and 5 (left and right next to 2) carry the two cores, pins 1 and 3 are not used. MIDI cables should have a maximum length not exceeding 45 feet.
5.5 Operating level Switch
To adapt the FEEDBACK DESTROYER PRO to the used operating level, the unit can be switched between homerecording level (-10dBV) and professional level (+4dBu). Use the LED bars on the frontpanel to determine the optimal setting. The Level indicators should read somewhere between -10 and -6dB, while the clip LED should not light up at all.

6. APPENDIX

6.1 Frequency chart
In order to maintain a better survey only every second value is registered in the table. The adjustable values do not exactly fit into a 1/60 octave interval, because also the ISO frequencies do not perfectly fit into a physical 1/3 octave interval. Rather a linear approximation is used to specify the values. Background f1,f2,. ISO frequency 1 third = 20/60 octave (idealized ISO interval) increment
+4/26.3 33.+6/60 21.34.+8/27.6 34.+10/60 Display 22.5 28.3 35.57 71.160 Hz Hz Hz Hz Hz Hz Hz Hz Hz Hz
+2/60 20.5 25.7 32.12850 16400
Display Hz Hz Hz Hz Hz Hz Hz Hz Hz Hz
-9/60 22.8 28.6 36.2 45.72.1138 1443

-8/28.9 36.14600 18400

-6/60 23.5 29.6 37.14950 18800

-4/30.2 38.15300 19200

-2/60 24.5 30.9 39.15650 19600

ISO 31.20000

.20 kHz.25 kHz.32 kHz.40 kHz.50 kHz.63 kHz.80 kHz 1.00 kHz 1.25 kHz 1.60 kHz
.20 kHz.25 kHz.32 kHz.40 kHz.50 kHz.63 kHz.80 kHz 1.00 kHz 1.25 kHz 1.60 kHz 2.0 kHz 2.5 kHz 3.2 kHz 4.0 kHz 5.0 kHz 6.3 kHz 8.0 kHz 10.0 kHz 12.5 kHz 16.0 kHz 20 kHz
2.0 kHz 1820 2.5 kHz 2275 3.2 kHz 2858 4.0 kHz 3618 5.0 kHz 4550 6.3 kHz 5715 8.0 kHz 7235 10.0 kHz 9100 12.5 kHz 11375 16.0 kHz kHz 18200
Tab. 6.1: frequency chart

6.2 Preset table

Preset Filter 1 Filter 2 Filter 3 Filter 4 Filter 5 Filter 6 Filter 7 Filter 8 Filter 9 Filter 10 Filter 11 Filter 12

L R SI SI

MONO: 9 single shot filters attenuate room resonances before 3 automatic filters destroy variable feedbacks SI SI SI SI SI SI SI SI SI SI SI SI SI SI SI SI AU AU AU AU AU AU
2 x MONITOR AS FEEDBACK DESTROYER ONLY: 7 single shots / 5 automatic filters for most monitor setups SI SI SI SI SI SI SI SI SI SI SI SI AU AU AU AU AU AU AU AU AU AU

L R AU AU AU AU AU AU

MONO AUTO PILOT: 12 Filters per channel constantly chase and destroy feedbacks. AU AU AU AU AU AU AU AU AU AU AU AU AU AU AU AU AU AU

Couple 125 Hz 160 Hz

STEREO PARAMETRIC EQ: Preset with 12 ISO frequencies, all set to 1/3 Oct., Gain + 0 dB 200 Hz 250 Hz 315 Hz 400 Hz 500 Hz 630 Hz 800 Hz 1k 1.25 k 1.6 k

Couple 40 Hz 63 Hz

STEREO PARAMETRIC EQ: Preset with 12 ISO frequencies, all set to 2/3 Oct., Gain + 0 dB 100 Hz 160 Hz 250 Hz 400 Hz 630 Hz 1k 1.6 k 2.5 k 4k 6.3 k

L R SI SI SI SI

2 x MONO: Sample monitoring, left for handheld (lead) microphone(s), right for fixed (backing) ones SI SI AU SI AU SI AU AU AU AU AU AU PA def PA def PA def PA def PA def PA def PA def PA def

L R SI SI SI SI SI SI

MONO PARAMETRIC AND SINGLE SHOT FILTERS: A good start for a monitor equalization SI SI SI SI SI SI SI SI SI SI PA def PA def PA def PA def PA def PA def PA def PA def
Couple PA 40 Hz 1 Oct. -8 dB PA 80 Hz 1 Oct. -4 dB
STEREO FOH EQ, providing 4 parametric EQs (low roll off in filter 1 and 2), plus 8 single shot filters PA d. PA d. SI SI SI SI SI SI SI SI
Channels coupled, changes on one channel are valid for both
L, R SI SI SI SI SI SI SI SI SI SI SI SI SI SI AU AU AU AU PA PA

MONO FREE PA PA PA PA

Couple SI SI SI SI SI SI SI AU AU PA

STEREO FREE PA PA

Tab. 6.2: Factory presets

6.3 MIDI implementation

Parameter Name Display Range Midi Control Number Control Value Range Couple Filter Select 1.12 Filter Mode OF, PA, AU, SI Engine Frequency 20 (Hz).20 (kHz) Fine (1/60 Oct) -9.+10 Bandwidth 1.120 Gain -48.+16 Feedback Threshold -3.-9 Store 1.10 In/Out 0.11 0.3 0,1,2 0.30 0.19 0.119 0.64 0.6 0.9 0.2 Left

LEDs Right IN on

IN off

IN flashing

Tab. 6.3: Controller functions with MIDI

Function

Basic Channel Mode Note Number Velocity After Touch Default Changed Default Messages Altered True Voice Note ON Note OFF Keys Chs

Transmitted Recognized

FEEDBACKDESTROYER PRO DSP1100P

Technical Specifications

Version 1.1 May 2000

www.behringer.com

ENGLISH

FEEDBACKDESTROYERPRO

Ultra-high performance 2-channel digital Feedback Destroyer / Parametric EQ powered by a 24-bit high-speed DSP
s 20-bit A/D and D/A converters with 64/128 times oversampling for ultra-high headroom and resolution s Automatically and intelligently searches out and destroys up to 12 frequencies per channel s 24 fully programmable Parametric Filters that can be set manually or via MIDI
s Set-and-forget default setting enables immediate and super-easy Feedback Destroyer performance
s Single-Shot mode automatically searches and destroys feedback and locks the filter until you reset them manually s Auto mode continuously monitors the mix, resetting programmed filters automatically
s Manual mode allows for setting up to 2 x 12 fully parametric filters including Frequency, Bandwidth and Gain s Single-Shot, Auto and Manual modes are assignable for each filter
s Free FEEDBACK DESTROYER software allows for total remote control via PC (download at www.behringer.com) s Two software engines give you independent or coupled functions on left and right channels s Internal 24-bit processing with professional 46 kHz sampling rate
s Servo-balanced Inputs and Outputs on gold-plated XLR and TRS Jack connectors for high signal integrity s Full MIDI capability and user preset memories to store programs for instant recall
s Accurate eight-segment LED level meters simplify level setting for optimum performance s Future-proof software-upgradeable architecture
s High-quality components and exceptionally rugged construction ensures long life and durability s Internal power supply design for professional applications s Manufactured under ISO9000 certified management system 2

DSP1100P

SPECIFICATIONS
Analog Inputs Connectors Type Impedance Nominal Operating Level Max. Input Level Analog Outputs Connectors Type Impedance Max. Output Level System specifications Bandwidth Noise THD Crosstalk MIDI Interface Type Digital Processing Converters Sampling Rate Display Type Power Supply Mains Voltages
XLR and 1/4" jack RF filtered, servo balanced input 60 kOhms balanced, 30 kOhms unbalanced -10 dBV to +4 dBu +16 dBu at +4 dB nominal level, +2 dBV at -10 dBV nominal level XLR and 1/4" jack electronically servo-balanced output stage 60 Ohms balanced, 30 Ohms unbalanced +16 dBu at +4 dB nominal level, +2 dBV at -10 dBV nominal level 20 Hz to 20 kHz, -3 dB > 94 dB, unweighted, 20 Hz to 20 kHz 0.0075 % typ. @ +4 dBu, 1 kHz, Gain 1 < -76 dB 5-Pin-DIN-Socket IN / OUT / THRU 20-bit Sigma-Delta, 64/128-times oversampling 46.875 kHz 2 -digit numeric LED-Display USA/Canada 120 V ~, 60 Hz U.K./Australia 240 V ~, 50 Hz Europe 230 V ~, 50 Hz General export model 100 - 120 V ~, 200 - 240 V ~, 50 - 60 Hz 100 - 120 V ~: T 125 mA H 200 - 240 V ~: T 63 mA H max. 15 Watts Standard IEC receptacle app. 1 3/4" (44.5 mm) * 19" (482.6 mm) * 7 1/2" (190.5 mm) app. 2 kg app. 3 kg
Fuse Power Consumption Mains Connection Physical Dimensions (H * W * D) Net Weight Shipping Weight
BEHRINGER is constantly striving to maintain the highest professional standards. As a result of these efforts, modifications may be made from time to time to existing products without prior notice. Specifications and appearance may differ from those listed or illustrated.
The information contained in this sheet is subject to change without notice. No part of this sheet may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying and recording of any kind, for any purpose, without the express written permission of BEHRINGER Spezielle Studiotechnik GmbH. BEHRINGER and FEEDBACK DESTROYER are registered trademarks. ALL RIGHTS RESERVED. 2000 BEHRINGER Spezielle Studiotechnik GmbH. BEHRINGER Spezielle Studiotechnik GmbH, Hanns-Martin-Schleyer-Str. 36-38, 47877 Willich-Mnchheide II, Germany Tel. +49 (0) / 92 06-0, Fax +49 (0) / 92 06-30