Stereo Mic techniques

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STEREO RECORDINGwith DPA Microphones


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ContentsStereo Boom for DPA Microphones 4

Background on two-channel stereo 5

Setups for stereo: AB 6

Setups for stereo: XY 8

Setups for stereo: Near coincident 9

- ORTF 11

- DIN 12

- NOS 13

Service & warranty 14

STEREO RECORDING

with DPA Microphones


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The UA0836 Stereo Boom (g 1) is a precision-craftedmicrophone boom for easy and secure mountingof microphone pairs for stereo recording It can beprecisely adjusted for both spacing and angling ofthe microphones

The boom can be mounted on a stand or suspendedfrom wires It has centimeter graduations on theboom and angle graduations on the microphoneholders for precise, quick and easy conguration ofthe recording setup

The holders supplied with the UA0836 are theUA0961 Microphone Holders (g 2), but can also besupplied without microphone holders as UA0837Apart from that, the UA0897 Shock Mount (g 3)can be used For arrangement of a coincident XYstereo or near coincident (including ORTF or NOS)stereo conguration, the stereo boom can be tted

with two directional microphones and DUA0019Spacer for Stereo Boom (g 15)

Mounting on a stand (g. 4)

Simply use the centered standard microphonethread or connect using the 3/8 NS27 threadadapter supplied

Suspension (g. 5)

Suspension of the boom is easily made by usingthe y eyelets at the ends of the bar Position theholders up-side down to obtain balance

Stereo Boom for DPA Microphones

Fig. 3 UA0897Shock Mount

Fig. 5 Flying theboom on wires

Fig. 2 UA0961Microphone

holder

Fig. 4 Mountingthe boom on a

microphone stand

Fig. 1 UA0836Stereo Boomwith holders

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How to determine spacing and angling

The stereophonic recording techniques are based onthe knowledge of how directional information is per-ceived by the human hearing system: When repro-duced by loudspeakers in a two-channel system, therst arriving, and/or the strongest sound produces thisdirectional information to the listener

Psychoacoustic research [1] has quantied the timeand level differences adequate for directional imagingto any position on the line between left and right loud-speaker in a standard loudspeaker setup (g 6)

The result can be seen from the curves in (g 7)If no time or level differences between left andright are present, the sound source is reproducedat 0 (hard center) To make a sound source appearat 30, the level difference between left and rightchannel should be 15 dB Also the sound appears

at 30 if the time difference between left and rightchannel is 112 ms (milliseconds)

Additionally, a combination of time difference andlevel difference can act together For instance thesound will be reproduced at 30 if the signal in onechannel is delayed by 05 ms and the level is ap-proximately 6 dB below the other channel (see dot-ted lines in g 7)

As mentioned, stereo recording is not just a questionof reproduction at hard left or right Naturally the in-between distribution is important, otherwise angledistortion will occur (g 8)

In g 7 the inter channel differences adequate for 10and 20 reproduction respectively are also found

First quantied, this information can be combinedwith the directional characteristics of the units in a two-microphone setup Then it is possible to determine theoptimum positioning of the microphones for a stereorecording

Background on two-channel stereo

Fig. 6 Setup for stereo listening

Fig. 7Inter channel differences to providea specic directional information

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B

A B C D E

B

DC

C D

Left Speaker Right Speaker

A B C D E

A

A

E

E

Fig. 8Angle distortion 3 different examples,showing irregularities between original soundsource placement and perceived localization


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AB stereo recording uses a spaced pair of omni mi-crophones On the boom, the microphones are nor-mally mounted keeping the housings in parallel

The distance from the centre of the thread to the cen-terline of the microphone can be read on the bar at

the outer side of the two holders respectively, (g 11)

The AB setup provides a nice reproduction of thereverberant sound eld and provides useful spatialinformation The directional information is slightlyless distinctive compared to other setups

AB is generally not suitable for mono as thesummed signal may suffer from comb ltering (Formono, just use one of the channels)

The spacing between two omni microphones canbe chosen from the curves in (g 9)

The scale on the horizontal axis indicates the timedifference between the microphones in millise-conds and the scale on the vertical axis indicatesthe position (width) of the sound source to be re-corded in degrees (g 19)

Procedure

The rst step is to select a distance between thesound source(-s) and the microphone setup Pleasenote that the ideal distance from the microphonepair to the sound source depends not only on the

type and size of the sound source and on the sur-roundings in which the recording is to be made,but also on individual preference

The mix of direct and diffuse sound in a recording isalso of crucial importance Therefore, considerabletime should be used in establishing the optimumpositioning of the microphonesBe aware, that all directional information from theroom will be reproduced in front of you in a 2-chan-nel stereo playback system Placement of the AB set-up closer than expected, will consequently give amore appropriate direct to diffuse sound balance It

is also here the versatility of our AB Stereo Kits canbe considered Using the different acoustical modi-cation devices for the microphones, the amount ofambience and the tonal colour of the recording canbe adjusted without adding any noise The choiceof oor and ceiling mounting of the boom givesyou added exibility when positioning the micro-phones

Omnidirectional microphones and AB Stereo areoften the preferred choice when the distance be-tween the microphone and the sound source islarge The reason is that omnidirectional micro-phones are able to capture the true low frequen-cies of the sound source regardless of the distance,

while directional microphones are inuenced bythe proximity effect Directional microphones willtherefore typically exhibit loss of low frequencies atlarger distances

Now we turn to the diagram, (g 9): Measure theangle under which the sound source(s) can beobserved, normally called the recording angleIf the total angle is say 140 this should be referredto as 70 Now, decide on the reproduction angleand nd the related distance between the micro-phones

Example: The recording angle is 70 This should bereproduced at 30 (time difference approximately11 ms) The crossing point is marked (): Hence thespacing should be 40 cm (16 in)

Setups for stereo: AB

DPA Microphones suited for this setup:

DPA 4003, DPA 4006, DPA 4006-TL, DPA 4004, DPA 4007and DPA 4041*

* Since the 4041 Large Diaphragm Microphone is not com-pletely omnidirectional at higher frequencies and has an on-axis upper midrange frequency lift, the perceived directiona-lity will change compared to most other omni microphonesIt calls for a little deviation from the graphs shown For posi-tioning circumstances, the 4041 can be considered as a widecardioid microphone (g 21)

Fig. 9: Diagram to determine the distance between twoomni microphones for the AB setup

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Left output

Fig. 10: AB setup

Fig. 11:The distance from the center is read on the outer side of the holder

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Setups for stereo: XY

XY stereo recording uses a coincident pair of di-rectional or bidirectional microphones, hence thedirectional information is obtained solely from thelevel difference between signals

In practice, coincident means that the micro-phone capsules must be placed close and slightlyabove each other In order to keep identical ver-tical aiming of the microphones, the DUA0019Spacer for Stereo Boom (g 15) should be used

Please note: Avoid the microphones touching eachother as this might cause mechanical noise

The XY setup provides a stable directional imagebut produces a slightly weaker impression of spaceand reverb compared to the AB setup

Be aware, that directional microphones exhibit low

frequency loss at larger distances and will resultin a lack of richness and energy in sound colourContrary to AB there are no comb ltering effectssumming XY signals to mono

In the most commonly used XY setup, a pair of rstorder cardioid microphones (eg DPA 4011-TL) arearranged in a 90 angle (45) This angular posi-tion is marked on the holders (g 13)

The sliders are marked XY for a 90 angular position

Other angles than 90 can be used for a XY setup,causing a change in the recording angle

Procedure

At rst, decide on the microphone position Dene theangle under which the sound source can be seen fromthe microphone position This is the recording angle(g 19) Then use the set of curves in g 14

The scale on the horizontal axis indicates the re-cording angle and the scale on the vertical axisindicates the level difference

The curves in the diagram express the angle be-tween the microphones

Example: The recording angle is 70 and thisshould be reproduced at 30 These two valuesmeet the curve at the mark This shows that theangle between the microphones should be 120

When recording an acoustic guitar for example,

the width of the image might be reduced in themix, so the desired microphone technique shouldnot produce any artifact like comb lteringThe XY setup provides these qualities Place themicrophones at a distance of approximately 40 cm(16 in) from the sound hole of the guitar and infront of 12th fret

Fig. 15:

DUA0019Spacer forStereo Boom,19 mm (075 in)

Fig. 12:XY setup

Fig. 16: Mounting microphonesclosely, but without any physicalcontact

Fig. 13: Marking for XY

Fig. 14: Set of curves to determine the angle betweentwo cardioid microphones for the XY setup

8DPA Microphones suited for this setup:

DPA 4011, DPA 4011-TL, DPA 4012

Left outputRight output


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Setups for stereo: Near coincident

It is possible to combine the principles of AB andXY in setups normally referred to as near coinci-dent Some successful congurations are namedafter the institutions that used them rst, likeORTF (Ofce de la Radio et de la Tlvision Fran-aise), NOS (Nederlandse Omroep Stichting), DIN(Deutsche Industrie Norm), etc

The advantage of near coincident techniques is thecombination of good ambient reproduction withprecise image positioning

The microphone capsules must point away fromeach other since the left microphone must re-produce left information earlier and louder thanthe right microphone and vice versa The 19 mmspacer (DUA0019) must be used whenever the mi-crophones cross each other (g 17)

When using the UA0897 Shock Mounts it maybe necessary to use the female XLR connector onthe cable in one of the rubber mounts, since theshock mounts take up more space than the nor-mal holders (g 18)

Fig. 18:

XLR connector suspension

Fig. 17:

When the mics are crossed, the 19 mm spacermust be used

Distance/Spacingbetween microphones

Anglebetween

microphones

Recordingangle

e.g. orchestra or choir

Fig. 19:

Difference between recording angle, spacing between micro-phones and angle between microphones

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Fig. 20Near coincident setup using rst order cardioidmicrophones

Fig. 21Near coincident setup using wide cardioidmicrophones

Near coincident setup in general

When dening the position of the stereoimage it is easy to place the outer limits -the edge of the image - and it is easy toplace the center However, in between thecenter and the outer edge there may occura small misplacement, typically 4-10 degrees

This is called angular distortion One of theadvantages of the near coincident setup isthe possibility of minimizing the angulardistortion Figures 20 and 21 show howmicrophone spacing and angling can beselected individually The scale on the hori-zontal axis is related to spacing, and thevertical scale is related to angling On eachcurve a number of circled gures are shownindicating the theoretical angular distortionof the different combinations of distance andangle

Example, cardioid microphones: A recordingangle of 70 can be achieved by spacing thecardioid microphones 20 cm (787 in) and bya 50 angling

Example, wide cardioid microphones: A re-cording of 70 can be achieved by spacingthe cardioid microphones 20 cm and by a90 angling

DPA Microphones suited for this setup:

DPA 4003, DPA 4006, DPA 4006-TL, DPA 4004, DPA4007 and DPA 4041*

* Since the 4041 Large Diaphragm Microphone is notcompletely omnidirectional at higher frequenciesand has an on-axis upper midrange frequency lift,the perceived directiona-lity will change comparedto most other omni microphones It calls for a littledeviation from the graphs shown For positioningcircumstances, the 4041 can be considered as a widecardioid microphone (g 21)

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This setup uses two rst order cardioid microphonesspaced 17 cm (7 in) and angled 110 (Fig 22)(The DUA0019 spacer must be applied)

The idea behind this technique is that it is well suited forreproducing stereo cues that are similar to those that are

used by the human ear to perceive directional informa-tion in the horizontal plane The spacing of the micro-phones emulates the distance between the human ears,and the angle between the two directional microphonesemulates the shadow effect of the human head

The ORTF stereo technique provides the recording witha wider stereo image than XY stereo while still preservinga reasonable amount of mono information Be aware,that directional microphones exhibit low frequency lossat larger distances and will result in a lack of richnessand energy in sound colour

If using the UA0897 Shock Mount, additional XLR exten-sion units must be applied as well, see g 18 The slidersare marked for the ORTF angular position

In recording a grand piano for example, placing the ORTFsetup in the curve of the pianos with the lid on full stickwill usually produce a very direct sound and a good ba-lance between the low key and the high key sound of theinstrument

110

170 mm

Right output Left output

Fig 22:ORTF setup

Fig. 23:

The ORTF setup marked in a general

diagram for cardioid microphones

ORTF

DPA Microphones suited for these setups:

DPA 4011, DPA 4011-TL, DPA 4012

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90

200 mm


Fig. 24:DIN setup

Fig. 25:

The DIN setup marked in a generaldiagram for cardioid microphones

DIN stereo uses two rst-order cardioid microphonesspaced 20 cm (78 in) apart and angled at 90 to createa stereo image (g 24)

The DIN stereo produces a blend of intensity stereo sig-nals and time delay stereo signals, due to the off-axis at-

tenuation of the cardioid microphones together with the20 cm spacing Be aware, that directional microphonesexhibit low frequency loss at larger distances and will re-sult in a lack of richness and energy in sound colour

The DIN stereo technique is more useful at shorter dis-tances, for example on piano, small ensembles or usedfor creating stereo on an instrument section in a classicalorchestra

When recording a choir for example, the perfect balancebetween the direct and the diffuse sound eld, using car-dioid microphones, can be accomplished at a distance

that leaves you with a recording angle of approximately100 The reproduced image of the choir should be evenlydistributed between the left and the right loudspeaker

DIN stereo


DPA 4011, DPA 4011-TL, DPA 4012

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90

300 mm


Fig. 26:NOS setup

Fig. 27:

The DIN setup marked in a general diagram forcardioid microphones


DPA 4011, DPA 4011-TL, DPA 4012

The NOS Stereo Technique uses two rst order cardioidmicrophones spaced 30 cm (118 in) apart and angled at90 to create a stereo image, which means a combina-tion of difference-in-level stereo and difference-in-timestereo

Be aware, that directional microphones exhibit low fre-quency loss at larger distances and will result in a lack ofrichness and energy in sound colour

When making an overhead recording of a drum kit, youmight want to create a widespread image In this casethe NOS setup is a good solution and can be achievedby simply placing the microphones approximately 50cm (20 in) above the cymbals

NOS

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Specications

Holders:UA0961

Shock mount:UA0897

19 mm spacer:DUA0019

Stereo Boom Specications

Length: 54 cm (21 in)Weight: 376 grams (13 oz) (w/o holders)Colour: BlackThread: 3/8 - NS27 (standard microphone thread)

Accessories:

References1 Simonsen, Gert Doctoral thesisTechnical University of Denmark

2 Williams, Michael: The Stereophonic Zoom1991 Published by author

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Products from DPA Microphones are extremely stable and there should not be any signicant changein the specications with time and use If, however, you are not totally satised with the characteristicsexhibited by these products, contact your nearest DPA Microphones representative for further detailsof service and the repair facilities that are available Please contact DPA Microphones for your nearestrepresentative on:

TEL: + 45 48 14 28 28

FAX: + 45 48 14 27 00

You can also get in touch with DPA Microphones at:info@dpamicrophonescomor visit our website at:wwwdpamicrophonescom

Environmental PolicyThis product is comprised by the Waste (WEEE) directive and should not be thrown in the garbage binwhen obsolete Instead, return it to your local DPA representative (or DPA Microphones A/S directly)who will dispose of the product in accordance with the current environmental standards

WEEE directive: 2002/96/EC

RoHS directive: 2002/95/EC

CE-MarkingThe CE-mark guarantees that the product conforms with relevant Directives approved by the EuropeanCommissionEMC Directive: 89/336/EC, amended by 92/31/EC and 93/68/ECLow voltage Directive: 73/23/EC, amended by 93/68/EC

2006 DPA Microphones A/S

product features and specications are subject to change without notice

Service & Repair


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Headquarters:

DPA Microphones A/S

Gydevang 42-44

DK-3450 Alleroed, Denmark

Ph: +45 4814 2828Fax: +45 4814 2700

[email protected]

www.dpamicrophones.com

United States:

DPA Microphones, Inc.

2432 N. Main St., Suite 200

Longmont, CO 80501, USA

Ph: +1 303-485-1025

Fax: +1 303-485-6470

[email protected]

Stereo Mic techniques

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