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The Ins & Outs ofInserts .........................2

Tale of theAux Return.................. 3

Physics: Simple, Phun,Usephul Phacts...........4

Humor: TransientResponse..................... 5

Feedback and thecommon mic ...............8

M AC K I E D E S I G N S Q UA R T E R LY G U I D E T O B L E S S E D M I X I N G S

INSIDE:

Summer

1997

Cure yourself ofknob-phobia

o those who have not spent their livesattached at the finger tips to a mixing

console, the sight of all those knobs andbuttons can be daunting. Dont be intimi-dated nuclear physics or brain surgerycan seem a little complicated too, at first

glance. But armed with an understandingof a few basic principles, and with a littlepractice well, getting around on the mix-

ing console need not be a problem.Getting over being intimidated by all

those knobs and buttons is fairly easy.

Divide controls into functionalsections.

The first step is to realize that the consolecan usually be divided into just a few basic

sections. Most mixer controls can be identi-fied as belonging to either aninput section known at Mackie as channel strips oramaster section.

Input Section (Channel Strip) ControlsA channel strip is generally comprised of

the following features:Trim.Here you adjust the level of the in-

coming signal to that which is optimum formixing. By proper trim adjustment you can

prevent the addition of noticeable noiseand avoid overload distortion.

Aux Sends (Monitor or Effects).Think ofthe aux (auxilliary) sends as level controlsfor additional mixes of your audio sources. Ifyou mix on a Mackie SR244, for example,

you can perform six auxilliary mixes in addi-tion to your main mix. These aux sends maybe routed to an outboard effect (such as re-

verb, delay, etc.), and returned to be addedto the main mix, or they may be used toperform a monitor, recording, assistive lis-tening, or broadcast mix.

EQ.Ahhh, the great equalizer. EQ comesin many forms, but basically is a way of in-creasing or decreasing the amplitude of acertain frequency range within a signal.The bass and treble knobs on your homestereo are essentially EQs. Some mixers, in-cluding most Mackie models, have Low CutFilters that cut all signal below a certainfrequency. These tend to be used on chan-nels with mics because they can helpeliminate mic thumps, wind noise, etc.

Signal Routing.These controls include: Pan,used for placing a source to the left, center, or

T

continued on page 6

Gobs of knobs on the CR1604-VLZ. Dont let em scare you!

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2Mackie Church Sound Notebook

OThe ins and outs of Inserts

ne of the features often found onthe rear panel of a mixing con-

sole is the Channel Insert. The insertserves simultaneously as both an in-put and an output for either a single

channel or for some other signal path,such as a submix or main output bus.It is a point in the signal path atwhich the signal can be detoured

sent out of the mixer and then re-turned to its normally scheduled pro-gramming, creating what is called aneffects loop. In other words, it allowsyou to insert an outboard deviceinto the signal path. (Like a 10HPEvinrude. Or, more likely, a reverb.)

On the Mackie SR408large-for-mat mixing console, each insert pointincludes a separate output and inputjack. On most mixers, however, asingleWthree-conductor jack pro-vides connections for both an inputand an output.

What would you do with such astrange jack?

Apply effects to a channel orsubmix.Because an insert is both aninput and an output, you can routethe signal from the channel out to areverb, compressor, limiter, etc., andthen back into the channel. You mightsend the signal to a noise gate unit inorder to automatically turn off a micwhen its not in use. Reducing thenumber of mics that are on, or open,reduces the risk of feedback and im-proves your signal-to-noise ratio.

Use it as a direct out(post micpreamp, but pre low cut filter, mute,EQ, fader, etc.). Just because youresending something out doesnt meanyou have to bring it back. You can use

each insert to send a direct out sig-nal to a line-level input of a tape re-corder, or to another mixer for abroadcast or recording feed. At the

mixer end of your direct out cable,youll want a standardWmono (orTS, tip/sleeve) phone plug. Push thephone plugpart wayinto the insertjack, just to thefirst click. This willroute the direct out signal via thecable, without interrupting the signalflow in the mixer. If you insert theplug all the way to the second click,you will still get a direct out signal,but the signal in the channel will beinterrupted at that point removedfrom the mix.1

Send a signal through a Y us-ing the insert as both a direct out andan effects loop.As an alternate ap-proach, create your effects loop as de-scribed earlier, then insert a Y

adapter afterthe processor to affect(compress, for example) both the di-rect out and the individual channel inthe mix. A good application for this

might be to compress apastors lav mic or a pulpitmic, in both the house mixand a recording or broadcast.

Whether you use them asa part of your normal setupevery week, or just to solvean occasional routing prob-lem, inserts add tremen-

dously to the versatility ofyour mixing console.

1 As an alternative to insertinga two-conductor plug half-way,you may choose to make a cus-tom cable which can be insertedall the way, but will still maintainsignal flow in the mixer channel.

To do this, use a three-conductorWTRS (ortip/ring/sleeve) phone plug instead of a two-conductor TS plug. Wire the TRS plug so thatthe tip and ring are bothwired to the center(positive) conductor of your shielded audiocable.

NOTE: Be sure to mark this cable in someobvious way to show it is for this special pur-pose only. It cannot be used with a balancedTRS jack without shorting the signal.

OUTPUT

INPUT andOUTPUT

INPUT

For use as an effects loop(TIP = SEND, RING = RETURN)

Ring inputfrom effects

Tip outputto effects

1/4"TRSPlug

1/4"TSPlug

MONOEFFECTS UNIT

1/4"TSPlug

MACKIE MIXERCHANNEL INSERT

RECORDEROR OTHERMIXER

OUT

OUT

OUT

IN

IN

IN

IN &OUT

OUT

1/4"TRS1/4"TS

EFFECTSDEVICE

(compressor,etc.)

1/4"TS

1/4"TS

MACKIEMIXER

CHANNELINSERT

Above: Standard Y cable with TRS to 2TS.Below: Two Y cables hooked together toallow effects to be fed to two separateplaces. Note that one Y is a TRS to 2TS,while the other has 3TS connectors.

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3 Mackie Church Sound Notebook

The Tale of the Aux Returno, this is not the story of the re-turn of the prodigal ox, this is

the story of the Aux Return. An aux(auxiliary) return is a line-level inputthat differs from the line inputs on

each of the channel strips in a coupleof ways. First, the aux return normallylacks a lot of the control features things like trim and EQ, for example.Second, aux returns are commonlyrouted directly to the main outputbus, where they are mixed with indi-vidual channel signals. Thus the ex-tent of control for an aux return ismost often a rotary level control. Letslook briefly at a couple of applicationsfor the aux returns.

The principle use of the aux return

is to bring a mix from an effects send(aka aux send) back into the consoleafter it has been enhanced (orabused) by an outboard signal pro-cessor, such as a reverb system. Theaux returns level control provides themeans of adjusting howmuch of that processed(wet) signal will be mixedtogether with the dry (orunprocessed) original signal.

OK, lets say youre doing asound reinforcement mix ofa couple of vocalists on aMackie MS1202-VLZ orMS1402-VLZ. Youre usingAux Send 1to provide amonitor mix for the singerswhile creating an effects mixon Aux Send 2. Fairly simpleso far. But now lets say thesingers discover how nicethe reverb sounds in the main mixand decide they could go for some ofthat in their monitors as well. Whats

a sound technician to do? Fortunately,theres an easy solution. Remember,however, you should never let on justhow simple such a feat might be;youll only spoil the musicians andtheyll keep on wanting more.

Adding reverb (or other effects)Heres how you can add reverb to

both the house and monitor mixes,with level control over the reverb con-tent of each.

1. Patch the Aux Send2output (ef-fects send) into the input of your reverb.2. Bring the reverb output (typically

two-channel) back into Aux Return 1,Left and Right. Do not plug anything

into Aux Return 2.

3. Depress the button marked EFXto Monitor, adjacent to the Aux Re-

turn 2level control. This routes thesignal at Aux Return2into the moni-tor mix, andinto the main mix.

Because Aux Return 1isnormalled1

to Aux Return 2, the reverb signalcoming into Aux Return 1will also be

present at Aux Return 2. You can noweasily control the amount of reverbcontent in your main mix with the

Aux Return 1level control, and theamount of reverb in the monitor mixwith the Aux Return 2level control.

Aux return as extra set of inputsAux returns can serve another

valuable function. One of the moreobvious considerations in selecting amixer is the required number of in-puts. People seldom buy a mixingconsole with the belief that it will not

handle all the audio sources in theirsystem. Still, it is hard to find a churchsound technician that hasnt occa-sionally wished for more inputs.

The aux returns on your mixer

might be just what you need at somepoint to easily add another stereo ormono line-level source to your mainmix. Here are some examples ofsources you might like to routethrough the aux returns:

Tape deck or CD player An ancillary mixer (submix of key

boards, other instruments, praiseteam, choir, etc.)

Audio tracks from a VCR Line-level output of a wireless mic

receiver

If youre bringing a monoline-levelsource into an aux return of yourMackie mixer, note that the Left AuxReturn 1input is also marked MONO.This means that the left channel isnormalled to the right channel. So

plugging your monosource into the Left in-put will give you thesame results as plug-ging it into both the Leftand Right. The ability touse the left channel of astereo input for routinga mono signal to bothchannels is common toall Mackie mixers.

So now you knowAux returns are more

than justWholes andfinely sculptured knobs.In fact, they may be just

the topic you need to enliven the con-versation at your next potluck dinner.Its almost guaranteed to provide youwith job security as the church soundoperator.

1Normalled means that, under normalconditions, spring-loaded contacts inter-connect these jacks so that the signal com-ing into Aux Return 1is shared with AuxReturn 2. When you insert phone plugsinto the Aux Return 2jacks, these connec-tions are broken, and Aux Returns 1and 2become independent.

N

The aux controls on the MS1402-VLZprovide great versatility.

:

AUX RET 1

Aux Return 1normalledto Aux Return 2

(i.e. receives same signal)

IN

L

R

AUX RET 2

L

R

OUT

OUT1/4"TS

REVERB UNIT

1/4"TS

OUT 1/4"TS

MACKIE MIXER

AUX SEND 2

1/4"TS

1/4"TS

1/4"TS

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Physics: Simple, phun, usephul phactshroughout history, man has writ-ten laws in an attempt to ex-

plain those forces within creationthat we are sort of, well, stuck with.Of particular interest to those of us

who mix audio should be certain lawsof physics having to do with the be-havior of sound. We shouldnt have topoint out that the laws of physics area little different than some of thoseother laws we encounter every day.You can choose to honor or violate adog-leash law, for example. Violationmay result in no more than a ticketand a lawn to clean. The laws of phys-ics, on the other hand, can only bebroken in Saturday morning cartoonsand in the sales literature of some lu-natic-fringe hi-fi equipment manu-facturers.

Inverse Square LawOne of the greatest tools in your

sound system operation arsenal is arule which describes a behavioral char-acteristic of sound. Known as InverseSquare Law, this tool costs nothing,takes up zero rack space, and requiresno regular maintenance. But under-standing Inverse Square Law can helpyou make intelligent microphone

placement decisions which can lead toreduced risk of feedback and dramati-cally improved recordings.

Inverse Square Law refers to theway sound levels decrease as youmove away from their point of origin.1

It should come as no major revelationthat the sound of a person speaking toyou from two feet away will be louderthan what you hear from a distance ofsix feet. But how much louder? Howgreat a change takes place?

Fortunately, there is a term to de-scribe the amount of change be-tween two such sound levels, or tocompare their strength. While theiractual amplitude is measured indynes/cm, a more practical way ofdiscussing sound is to refer to soundpressure levelor SPL. The unit used tocompare these levels is the decibel(abbreviated dB). A decibel is onetenth of a Bel.2When we hear a

sound that we perceive to be twicethe level of another, that difference isabout 10dB.

When we say that the SPL from aspeaker system is 80dB at the third

row back in the auditorium, we arealso comparing two levels.80dB SPL(or any SPL) is referenced or comparedto 0dB SPL, which is the theoreticalthreshold of hearing the softestsound level that can be heard by sen-sitive, young ears not yet subjected torock and roll. Note that 0dB does notindicate the absence of sound, justthat there is zero difference from thereference level.

Back to Inverse Square Law. Accord-ing to the law, the intensity of soundvaries inversely according to the

square of the distance. Simply stated,measured sound level will drop 6dBfor each doubling of the distancefrom the source.

Indoors, this drop in level from the

sound source will occur only to apoint referred to as Critical Distance(DC), at which the level becomesequal to that of the reflected soundfrom walls, ceiling and floor. This dis-tance varies with the acoustics of theroom and the directional characteris-tics of the sound source. The more re-verberant or live the room acoustics,the shorter will be the path to criticaldistance. As the sound source is made

more directional, critical distance ismoved farther out.

Beyond critical distance, the clarityof speech becomes adversely affected with intelligibility severely limited

for the listener seated too far back inthe reverberant field. One way ofdealing with this situation is to locatethe system speaker or speakers closerto the listeners. Care should be takenin using speakers in multiple loca-tions within the room, though; add-ing speakers can actually decreasein-telligibility by presenting the listenerwith multiple sound arrival times.

No doubt you have been in a highlyreverberant space, such as a gymna-sium, in which it was difficult to con-verse over a distance of only a few

yards. You probably noticed that youcould be understood better if youwould cup your hands to your mouth,making your voice more directional bycreating a small horn. Critical distance

can be increased by using highly direc-tional loudspeakers, adding absorptivematerial to room surfaces, or by re-moving the walls and ceiling. (The lat-ter being a last resort.)

Using the law to annihilatefeedback

Lets look at how a knowledge ofthe inverse square law can help you

T

wide coverage

Direct Sound Field

Direct Sound Field

Reverberant Sound Field

Reverberant Sound Field

narrow coverage

DC

= CRITICAL DISTANCEDC

DC

continued on page 5

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eliminate feedback. To do that, weneed to know what conditions bringabout feedback.

Feedback occurs when sound from asystems loudspeaker re-enters the mi-crophone at a level that is equal to or

greater than the level of the sound ar-riving from the original sound source.

So, if we can speak or sing louderinto a microphone than the level ofour amplified voice arriving back atthe mic, we win right?

Lets say we have a soft-spokenmissionary standing two feet fromthe microphone. Her voice producesan average SPL of 59dB at the mic,and our sound technician knows hemust amplify that to 75dB SPL at hismixing position in order for everyonein the auditorium to hear.

Well further assume that once thislevel has been achieved, themissionarys amplified voice arrivesback at the mic at 60dB SPL. Oursound technician will try in vain to re-inforce her voice without feedback.The technician inches the fader gentlyupward, the system begins to howl,and the missionary (who last saw asound system while on furlow in 1951)reacts by backing away from the mic,

making matters worse. Now there areonly two choices for the technician:3

throw the system into terminal oscilla-tion and run out the door, hands overears, screaming I cant take it any-more! or back off on the fader and ad-mit defeat. (If youre grading the tech-nician, choice B is the correct one.)

What are the possible solutions?First we can move the mic or the mis-sionary to bring them closer together.If we divide the distance in half, to onefoot, the level of the unamplified voice

at the microphone will be 65dB SPL a 6dB increase. Of course this will in-crease the system output level by 6dBas well. But when the operator de-creases the channel gain to the desiredlevel, the SPL from the loudspeaker atthe mic will once again be60dB, or5dBbelow the level of the voice. If the mis-sionary can be urged to step evencloser to the mic, say to a distance ofsix inches, the mixer gain may again

be lowered by 6dB. Now the voice willbe 11dB above the level of the ampli-fied sound at the microphone. It isgenerally considered good practice toalways operate your system at least6dB below the feedback point.

Feedback is a signal-to-noise ratioproblem. The greater the ratio be-

tween the levels of the desired signal(in this case, the amplified versionof the sound) and the unwanted sig-nal, the better. By simply decreasingthe distance between the soundsource and microphone, you can dra-matically improve your signal-to-noise ratio. This same principle, ofcourse, applies to controlling the pick-up of anyambient noise. If you are re-cording or broadcasting using a micthat is not connected to a speakersystem in the same room, feedback isnot a problem. But youll diminish thesounds of coughs, sneezes, babies, re-verberation, and snoring in your re-cording if you move the mic closer tothe sound source.

Other tools have you, which arenot of this article.

Keep in mind that there are othertools which can help you eliminatefeedback. Some of these include: a lin-ear microphone and loudspeaker fre-quency response, reduced system

bandwidth, directional microphonesand loudspeakers, and maintaining aminimal number of open microphones.Well be addressing each of these sub-jects inMCSN, as space permits.

The intelligent use of Inverse SquareLaw is often the tool you need to elimi-nate feedback or improve a recording.And, hey you cant beat the price.

continued from page 4 FOOTNOTES11111 Well try to keep this simple for the sakeof discussion, so we must warn the acous-ticians, physicists, and child prodigies thatwere taking the grenade approach to thistopic well get close enough to be veryuseful, while not losing most of our read-ers with confusing details. Inverse SquareLaw actually assumes that the soundsource radiates in all directions equally andthat there are no reflective surfaces for thesound to encounter.22222The Bel is named for Alexander GrahamBell. Not as well known is that Bell discoveredsound as he sat with his friend Isaac beneathan apple tree. A passing breeze loosened anapple which dropped onto Sir Isaac Newtonshead. Klunk! Sir Isaac was struck with theconcept of gravity, which he failed to patent,and Alex, sensing the gravity of the situation,realized the percussive potential of the KlunkHe soon invented the bell, an early percus-sion instrument in the church, and went on

to start the audio industry. (Early church bellswere called klunks, which was German forbonk. Refinements to the clarity of theirsound led someone to note that the klunknow sounded clear as a bell. After that, itjust seemed natural to refer to them as bells.Besides, the name had a nice ring to it. Thereis no connection between this old saying andAlexanders old spinster cousin Clarissa Bell.

Of course the lyrics of numerous songshave had to change over the years. Some ofthese included: Thud the Klunks, Thud theKlunks, Let the Whole World Know, I Heardthe Klunks on Christmas Day, and Thud

the Klunks of Heaven, There is Joy Today.33333 The suggestion has been made that theenterprising sound tech might find a thirdoption. Noting the distress of the congre-gation, as evidenced by the gloweringfaces rotated in the direction of the controbooth, the imaginative tech might use thisopportunity to take up an offering for newsound equipment on the pretense that italone can eliminate the feedback. :

TRANSIENT RESPONSE*

Wow! Lookslike the cockpitof a747!

*The unsolicited commentsof congregation members

as they pass by the mixer.

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right in the stereo horizon; Channel As-signment switches, which allow you toassign a channel to specific submixes;Mute, which turns off the channel;and Solo (or Cue or Monitor), which al-lows you to monitor the channel onheadphones or control room monitors,without affecting the mix.

Fader (level control).The fader is theslide control that allows you to adjustthe amount of signal that appears inthe main mix. While the trim control isused to adjust incoming signal levelsto be nearly the same to establish astarting point for the mix thefader allows you to adjust the relativelevels of all channels being mixed. (If

your mixer has a rotary, rather thanslide control, it may be referred to as again or simply level control.)

Other fun thingies:Some channelstrips include a Polarity switch, used toreverse the polarity of the incoming sig-nal. Each channel may also have itsown phantom power switch, which al-lows phantom power to be used onlywith those condenser mics that need it.

Learn one channel strip andya got em all

A mixer may have12

,14

,24

or even56channel strips. Thats a lotta knobs.But keep this in mind: most channelstrips are exactly the same. Asidefrom stereo channel/aux returnstrips, which tend to have a few lessknobs, and aside from some very ex-otic consoles, once you know onechannel strip you know them all.Youre halfway there already!

Master SectionSubmix Sends.You can usually as-

sign channels to specific submixes. Allof your backing vocals may be sent toone submix, and the rhythm sectionmay be sent to another. This is some-times called group mixing, as youcan control the relative levels ofgroups of microphones with just onefader per group.

EQ.Some mixers have a broadbandgraphic EQ section in the master area these are essentially system tonecontrols. This is most commonly seen in

combination mixer/amplifiers, where theadvantages of beingable to select a particu-lar external equalizer

may be offset by thedemand for portability.

Aux Returns.Usedto control the amountof signal being re-turned to the mixerfrom an outboard sig-nal processor or othersource. See The Tale ofthe Aux Return, page3.

Monitoring.Look inthe master section for

selector switches withwhich you determinewhat you hear in yourheadphones or studiomonitor speakers, andlevel controls that al-low you to adjusttheir volume.

Master Fader(s).Just as the name im-plies, this is your mas-ter level control, nor-mally used to adjust

the main mix Leftand Right signals thatgo to the amps and onto your PA speakers, orto a 2-track recordersuch as a DAT or cas-sette deck.

Practice and listen.One of the best

ways to become com-fortable with the con-sole is to spend a little

time with it in private.Just the two of you. Itneed not be an expen-sive night out; its qual-ity time that counts.

The purpose of thisexercise is to learncause and effect atsome more appropri-

ate time than during a worship service.Heres a good way to begin. First, youllneed a sound source, or a selection ofsound sources. There are two types ofsources you could use: one is an acous-tic source picked up by a microphone;the other is a direct source, such as tapeor CD. We suggest you begin by using atape or CD player, connected to a lineinput of your mixer.

Youll also need decent head-phones or some good quality studiomonitors connected to the controlroom or main mixer outputs. Bymonitoring the console output as di-rectly as possible, you will be able tohear qualitative changes as you make

them including subtle differencesthat would otherwise be obscured byroom acoustics or ambient noise.

The idea is to send your programsource through an input channel, playwith the various channel controls (EQ,pan, etc.), and monitor the results.You may want to connect your sourceto a stereo channel to do some ofyour tests and then connect to amono input to discover the differ-ences. The stereo and mono inputsmay differ, for example, in the EQ con-

trol available. Also, listen to how thepan (or balance) control differs on astereo channel from the pan on amono channel.

The area youll want to spend themost time with is the EQ. Listen to avariety of program material to deter-mine how your mixers channel EQ af-fects the sound of the signal. Some ofthe best recordings to use include:male speaking voice and solo record-ings of piano, violin and guitar. Thehigher the recording quality the better,

but almost any recording will give yousome idea of what your EQ will do.

Using recorded sound as yoursource, rather than a miked voice orinstrument, provides exact repeatabil-ity for comparison of different controlsettings. It also allows you to hear onlywhat the mixer settings are doing,without the confusion of hearing di-

Cure yourself of knob-phobiacontinued from page 1

continued on page 7A channel strip ofMackies CR1604-VLZ.

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MACKIE CHURCHSOUND NOTEBOOK

Volume 1, Number2

Summer 1997

Editor:GREG SILSBYLayout/Writing:MARSH GOOCH

Tech Patrol:DAVE FRANZWA, PAULLARSON, MACKIE TECH SUPPORT

Address all Letters to the Editor, subscrip-tion requests, and changes of address to:MCSN, 16220Wood-Red Rd. NE, Wood-inville, WA 98072 Subscriptions areFREE, so call or write us and let us knowyou want one. MCSN is a publication ofMackie Designs Inc. The following areregistered trademarks or trademarks ofMackie Designs Inc.: MACKIE., the Run-ning Man figure, VLZ Copyright 1997Mackie Designs Inc. All rights reserved.Printed in the USA.

continued from page 6

(relative to an omni) if the mic wereplaced in a diffuse sound field. This isreferred to as the Distance Factor, orDF. For example, lets say we have anomni positioned 10from our pastors

mouth, and that the sound we do notwant to pick up (sound from the

loudspeaker) is arriving from all direc-tions equally. Assuming that thepastors voice is louder at the micthan is the sound from the speakersystem, the difference between thetwo is the signal-to-noise ratio. Ofcourse if the loudspeaker wins, wehave a noise-to-signal ratio wealso have feedback.

Omnidirectional microphones aregiven an REE of 1.0 as a reference pointfor comparing other polar patterns.The cardioids REE,0.333, indicates that

it picks up just 1/3the energy that theomni picks up within a diffuse field.Because this reduced sensitivity is atthe sides and the rear of the cardioid,it is ambient noise, not signal, that islowered in level. The result is that thecardioid can achieve the same signal-to-ambient noise ratio as the omni ata distance 1.7times that of the omni,or 17in our example.

While the REE of a mic is good toknow, it should be understood thatthe figures on the chart are for math-ematically perfectmicrophones(micus nonexistus) in a totally diffusefield(environmentus acousticusnonexistus). While they are a good ba-sis for understanding, your mileagemay vary.

Proximity EffectDirectional microphones also differ

from omnis in another respect. As adirectional mic is brought close to a

small sound source (a human mouth,for example) the mics response be-comes non-linear, with lower fre-quencies emphasized. The frequen-cies affected, how much they areboosted, and the distance withinwhich proximity effect will occur, willvary with the design of individual

models. Because there is no boost ofsignals arrivingfrom a distance(such as thosereturning fromthe loudspeaker)proximity effectcan greatly re-duce feedbackpotential when amic is used closeto a soundsource.

Much of the boosted output resulting from proximity effect occurs inthe voice range, making male vocal-ists sound more grown up, or femalevoices more full. The boost in mic out-put may be 20dB or more in the loweportion of the spectrum, meaningcare must be taken to insure that thegain control at the top of your mixerschannel strip is properly set to com-pensate for the higher microphonelevel. Because the increased output is

predominantly low frequencies, youmay still suffer some intelligibilityloss, or may end up with a muddysound, even after you have adjustedthe gain control. If so, turn down thelow-frequency control on the channelEQ to restore a natural quality. Micro-phones designed specifically for closevocal use are often designed to havea rolled-off low frequency response,measured at a distance. When themic is used up close, as intended,proximity effect restores the low end.

Such mics may sound a bit anemic, ofcourse, when used at a distance.

continued from back page

:

Feedback

:

POLAR DISTANCE NULL ANGLEPATTERN REE FACTOR (DF) (DEGREES)

Omni 1.0 1.0 N/A

Cardioid .333 1.7 180

Supercardioid .268 1.9 126

Hypercardioid .25 2.0 110

Bi-directional .333 1.7 90

rect, unamplified sound, as you wouldexpect when mixing in an auditorium.

Focus on the controls youreactually using, or using the most.

One factor that should make thesea of knobs in front of you a littleless imposing is the fact that during atypical church service, relatively fewcontrols need to be touched. Many ofthe controls on your console are usedto pre-adjust levels or determine thedestinations to which signals will berouted. It is not unusual for an opera-tor to use only the mute buttons andfaders during a service. Trim controlsshould be set in advance and need tobe adjusted only if conditions changedramatically. Likewise, channel as-

signments to sub sends or main out-puts are normally set and left alone.Once channel EQ adjustments havebeen made for particular microphoneapplications, it is quite common forthere to be no need to adjust EQ fur-ther during the service.

The tip of the iceberg.Of course, theres a lot more to

mixing sound than we can get to inthis article. Thats what MCSNis for.Throughout this issue and future edi-tions, well further explore what ittakes to provide the best sound pos-sible for your congregation.

FOR OFFICIAL USE ONLY!

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Want to see our products in color? Want to see more hookups? Why not call us and ask for a copy of IN YOUR FACE?Tell em MCSN sent you.

Lavalier mic tips Whats in a NOM? RFI: What it is and what to do

about it

Answers to readers questions

16220 Wood-Red Rd. NEWoodinville, WA98072Toll-Free800-898-3211Fax 425-487-4337E-mail: [email protected]

Feedback and thecommon microphone

oure probably quite aware thatcertain microphones tend to con-

tribute less to feedback problemsthan do others. And you may have

wondered why one microphoneworks well two feet from a soundsource, while it is nearly impossible touse another at more than a fewinches without the system going intofeedback. Whats the difference be-tween the mics? Lets look at the rolemicrophone selection can play in ourattempts to reduce the potential forfeedback. To do this we need to learna little bit about the performancecharacteristics of different micro-phone types.

LinearityA microphone converts acoustic

energy (sound) to electrical energy. Ifit were able to do so with absolutelyequal sensitivity to all frequencies, wewould say it had a flat or linearfrequency response. A peak in amicrophones response curve indi-cates that the microphone is more

sensitive to some frequencies than toothers. This peak may cause feedbackto occur at those frequencies beforethe required system gain can be

achieved. A linear response is particu-larly desirable as the distance is in-creased between the microphone andthe sound source. Typical distant ap-plications include miking choirs, dra-mas, and childrens programs.

BandwidthThis has no connection to the girth

statistics of your praise band. It refersto how extended the response of themicrophone is. While we usuallyequate morewith better, a frequency

response of DC to purple is not neces-sarily a great thing. Low frequencyfeedback problems can often be elimi-nated by using a mic with a less ex-tended low-frequency response; somemics offer a bass roll-off switch to limittheir response. The Low Cut filter oneach channel of many Mackie mixerswill give you this control where youneed it, when you need it.

Polar patternsThe microphone polar pattern chart

(see page 7) reveals several thingsabout the ability of each microphone

type to reduce feedback. First, it tellsus the Random Energy Efficiency (REE)of the mic. REE is a measurement ofhow much energy a microphone picksup (relative to an omnidirectional mic)when subjected to all frequencies ofsound arriving with equal intensityfrom all directions. This is not an indi-cation of the mics sensitivityrating.

The REE dictates what the relativeworking distance of the mic would be

Y

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;www.mackie.com

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