THE EFFECTS OF INTERAURAL CROSSTALK 2420-B (B4 0)

ON STEREO REPRODUCTION (See also: Part 1,

AND Preprint 1/2420'A)MINIMIZING INTERAURAL CROSSTALK IN NEARFIELDMONITORING BY THE USE OF A PHYSICAL BARRIER:

Part 2 APPENDICES 1-10

Timothy M. BockCrown International, Inc.

Elkhart, Indiana

D. (Don) B. Keele, Jr.

Techron, Division of Crown International, Inc.

Elkhart, Indiana

Presented at A U D IO

the 81st Convention1986November 12-16Los Angeles, California ®

Thispreprinthasbeenreproducedfromtheauthor'sadvancemanuscript,withoutediting,correctionsorconsiderationbytheReviewBoard.TheAES takesnoresponsibilityforthecontents.

Additionalpreprintsmaybe obtainedby sendingrequestandremittanceto theAudioEngineeringSociety,60 East42ndStreet,New York,New York10165USA.

Ail rightsreserved.Reproductionof thispreprint,oranyportionthereof,isnotpermittedwithoutdirectpermissionfromtheJournalof theAudioEngineeringSociety.

AN AUDIO ENGINEERING SOCIETY PREPRINT

The Effects of Interaural Crosstalk on Stereo Reproduction

and

Minimizing Interaural Crosstalk in Nearfield Monitoring bythe Use of a Physical Barrier: PART 2

Timothy M. BockCrown International, Inc.Elkhart, Indiana 46517

D. (Don) B. Keele, Jr.Techron, Div. of Crown International, Inc.

Elkhart, Indiana 46517

APPENDIX 1: List of Recordings That Image Well .... 75

APPENDIX 2: Geometric and Timing Relationships forStereo Listening ................... 78

APPENDIX 3: Theoretical Sound Field at Listener'sEars for Amplitude Panned Signals in a NormalSpaced-Speaker Stereo Listening Setup ........ 83

APPENDIX 4: Theoretical Sound Field at Listener's

Ears for Delay Panned Signals in a NormalSpaced-Speaker Stereo Listening Setup ........ 88

APPENDIX 5: Theoretical Sound Field at Listener's

Ears for a Centered Signal in a NormalSpaced-Speaker Stereo Listening Setup with LateralShifts in Listener Head Position ........... 94

APPENDIX 6: Theoretical Sound Field at Listener's

Ears for a Spaced-Speaker Stereo Listening Setupwith Central Reflective Barrier ........... 99

APPENDIX 7: Theoretical Sound Field at Listener's

Ears for a Close Spaced-Speaker Stereo ListeningSetup with Central Reflective Barrier ........ 105

APPENDIX 8: Measurement Results for Standard Stereo

Setup in Lab ..................... 109

APPENDIX 9: Measurement Results for RecordingStudio Control Room ............. .... 114

APPENDIX l_: Measurement Results for

Recommended Barrier Listening Setup ......... 117

APPENDIX 1: List of Recordings that Image Well

The following list of recordings have been found to imagewell on the barrier setup. The list is in no waycomprehensive, and represents only those recordings that theauthors have in their own collection or have had personalcontact with.

For reasons of compactness, the listing is of compact discsonly. In most cases, the equivalent can be found on eitherLP or cassette.

............................................................

Performer(s): ZZ TopRecording Title: Eliminator

Company: WarnerCatalog Number: 9 23774-2

Best Track Selections: Tracks 4, 7Music Style: Rock

............................................................

Performer(s): Donald FagenRecording Title: The Nightfly

Company: WarnerCatalog Number: 23696-2

Best Track Selections: Ail, especially Tracks 2, 4, 8Music Type: Rock

Comments: Track 8 is topsl

............................................................

Performer(s): James MoorerRecording Title: Digital Domain

Company: ElectraCatalog Number: 9 60303-2

Best Track Selections: Most

Comments: Tracks 1, 3 (Lions are Growing) areextremely good!

Music Type: Computer synthesized soundsand Sound Effects

............................................................

Performer(s): Papa Doo Run RunComposer(s): Beach Boys

Recording Title: Good VibrationsCompany: Telerc

Catalog Number: CD-70501

Best Track Selections: Ail, especially tracks 5, 7Music Type: Rock

Comments: Track 7 is Tops!Performer(s): Herbie Hancock

Recording Title: Future Shock

75

Company: ColumbiaCatalog Number: CK 38814

Best Track Selections: Tracks 4, 6

Music Type: RockComments: Track 6 is topsl

Performer(s): Berlin Or. SuitnerComposer(s): Beethoven

Recording Title: Symphony No. 9 (Complete)Company: Denon

Catalog Number: 38C37-7021Best Track Selections: All

Music Type: Classical

............................. . ..............................

Performer(s): Pink FloydRecording Title: Dark Side of the Moon

Company: EMICatalog Number: CDP 7460012

Best Track Selections: Tracks 2 & 3 are knockoutslThe alarm clock going off in 3will knock your socks offl

Music Type: Rock

............................................................

Performer(s): Pepe Romero; Amsterdam Cone.Composer(s): Tarrega; Saint-Saens

Recording Title: Hear The LightCompany: Phillips

Catalog Number: ?Best Track Selections: Tracks 7, 8

Music Type: ClassicalComments: Track 7 has noticeable reverb effect

Performer(s): Philadelphia Orchestra;Cleveland Orchestra

Composer(s): Saint-Saens; Tchalkovsky;Beethoven, Gerswin; Stravinsky

Recording Title: Sampler Vol. IICompany: Telarc

Catalog Number: CD-80102Best Track Selections: Tracks 14-18

Music Type: Classical

76

Performer: Dave Grusin

Composer(s): Stewart; Grusin; RitenourRecording Title: Jazz Sampler Vol. I

Company: GRPCatalog Number: GRP-D-9509

Best Track Selections: Tracks 2, 3, 4Music Type: Jazz

Comments: Tracks 3, 4 are Tops!

............................................................

Performer(s): Thelma Houston & Pressure CookerRecording Title: I've Got The Music In Me

Company: Sheffield LabCatalog Number: CD-2

Best Track Selections: All goodMusic Type: Rock

............................................................

Performer(s): The Alan Parsons ProjectRecording Title: I. Robot

Company: Mobile Fidelity Sound LabCatalog Number: MFCD 804

Best Track Selections: MostMusic Type: Rock

......................... . ..................................

Performer(s): Ron Tutt; Jim KeltnerRecording Title: The Sheffield Track Record/

The Sheffield Drum RecordCompany: Sheffield Lab

Catalog Number: CD-14/20Best Track Selections: Tracks 5, 6

Music Type: InstrumentaiComments: Drum Solos!

............................................................

Performer(s): VariedRecording Title: Creme De La Creme

Company: Sheffield LabCatalog Number: CD-CRM

Best Track Selections: MostMusic Type: Rock

............................................................

Performer(s): Don DorseyRecording Title: Bachbusters

Company: TelarcCatalog Number: CD-80123

Best Track Selections: Most

Music Type: Synthesized Bach seleotions

77

APPENDIX 2: Geometric and Timing Relationships for StereoListening

Interaural Distance-Time Relationships for a Spaced-SpeakerListening Setup

Interaural distance-time relationships for a spaced-speakerlistening setup can be derived quite easily, as we willshow. Fig. 41 illustrates a normal spaced-speaker setup wlththe five basic dimensions we will use for this derivation.

As can be seen, H is the distance between a listener's ear;D is the distance between the loudspeakers; aD is theperpendicular distance from the listener's ears to the

loudspeakers; and d 1 and d 2 are the direct and interauralsignals, respectively, from the listener's ear to theloudspeaker. Pythagoras tells us that:

D H)2d I = aD)2 + ( _-

which, after mulLiplying, b_comes:

DV_4a2+ ') /. 2H + H2

dl = 2 _/ _ D (4a 2+ !) D2(4a 2+ !)

and, after de].eting the last term in .the square root may beapproximated bV:

D %_ 4a'2+ i ) HdI = (I )

2 D (4a2+ I)

For d 2 ,

_/_ D H )2= aD)2 + ( +d 2

which becomes the approximation:

D/V'(4a2+ !) Hd2 = (1+ )

2 D(4a2+I)

78

Therefore,

Hd2-d!=

_t_4a 2+ I)

For O= 60 ° , a = Vr_ .and d2- dl = H

2 _4a 2+ !)

H H

\/4(3) 2y_+ i

which is one-half the width of the head!

The approximation:

H

_/_4a 2+ I)

is valid only if:

H 2<< ! or H2<<D2(4a2+ I)

D2 (4a2+ !)

AS a check, assume H to be 6.75 inches, (approximatedistance between the human ears), D to be 120 inches(typical studio monitoring setup), and the angle between theloudspeakers to be 60 °.

H2 (6'75)2 45.565- = = 0.00 I

57,600.00D2(4a2+ I) (120)214(___) +!]

0.001 << I !

79

Allowable Listener Head Movement for the Barrier ListeningSetup

Theoretically, the maximum distance that the listener canmove from the barrier and still perceive a 180 ° sound stage

is intimately tied in with the size of the barrier andthe distance between the loudspeakers, as can be seen in

Fig. _2. Although we have not yet formally measured this totest-against the theoretical, we estimated during testingthe distance to be about that which was theorized.

Looking at fig. 42, one readily notices the existence ofthree similar triangles which meet at a point that theinteraural crosstalk intersects. Side adjacents of thetriangles represent the maximum distance that the listenercan move from the barrier (z + Y), and the width of the

barrier (x - y). T is the thickness of the barrier; H isthe distance between the human ears; and D is the distancebetween the loudspeakers. Because the triangles aresimilar:

._/__H_Tz_y er Z=-_ and Y--TX

· Thus, the maximum distance that the listener can move fromthe barrier is

TX X(H+T)maximum distance = _ + D O

Analysis of this equation shows that an increase in themaximum distance can be effected by either an increase in Xor T, or a decrease in D (H is a constant). In other words,

increasing the width or thickness of the barrier, and/ordecreasing the distance between the loudspeakers, increasesthe distance that the listener's ears can be from the

barrier.

8O

Geometric and Timin.qRelationships for Spaced-Speaker Listening Setup

Left I D _1 RightSpeaker Speaker

aD

Listener d I I

F,G. 41

81

Allowable Listener HeadMovement for the, Barrier

Listening Setup

-Left RightSpeakerSpeaker

TX

TZ

F_G.42_

82

APPENDIX 3

Theoretical Sound Field at Listener's Ears for AmplitudePanned Signals in a Normal Spaced-Speaker Stereo ListeningSetup

Data is shown for the theoretical effects of interauralcrosstalk, on the sound field that exists at the listenersear positions, for an amplitude panned signal. A centerlocated head is assumed. Both time and frequency responsedata is shown.

The data was generated using an Excel spreadsheet modelrunning on an Apple Macintosh computer. Model variablesentered included: speaker spacing, speaker level, speakerpolarity, speaker delay, head to speaker distance, and headlateral location. All levels are referenced to the

loudspeakers one-meter level. The standard stereo setup ofFig. 7 is assumed in every simulation.

Several values of level imbalance were modeled. These

values are noted on each figure. Note the reduction in comb

filtering peak-to-peak amplitude, in both ears frequencyresponse, as the signal is panned farther and farther to theside. Also note that the frequencies of the comb filterpeaks and notches do not change when the signal is amplitudepanned.

83

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APPENDIX 4

Theoretical Sound Field at Listenerms Ears for Delay PannedSignals in a Normal Spaced-Speaker Stereo Listening Setup

Data is shown for the theoretical effects of interaural

crosstalk, on the sound field that exists at the listeners

ear positions, for a delay panned signal. A center located

head is assumed. Both time and frequency response data isshown.

The data was generated using an Excel spreadsheet modelrunning on an Apple Macintosh computer. Model variables

entered included: speaker spacing, speaker level, speaker

polarity, speaker delay, head to speaker distance, and headlateral location. All levels are referenced to the

loudspeakers one-meter level, The standard stereo setup of

Fig. 7 is assumed in every simulation.

Several values of differential delay were modeled. These

values are noted on each figure. Note that the frequenciesof the comb filter peaks and notches changes heavily underthe effects of delay panning. Note also that the peak-to-

peak amplitude of the comb filtering does not change as aresult of delay panning (see following comment).

Be aware that the visual changes in notch level are a result

of the graphing process and not the modeled process. The

levels of the notches change b_cause their frequencies do

not correspond exactly with the sampled data points.

88

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APPENDIX 5

Theoretical Sound Field at Listener's Ears for a Centered

Signal in a Normal Spaced-Speaker Stereo Listening Setupwith Lateral Shifts in Listener Head Position

Data is shown for the theoretical effects of interaural

crosstalk, on the sound field that exists at the listeners

ear positions, for lateral shifts in the position of thelistener's head. Both time and frequency response data iashown.

The data was generated using an Excel spreadsheet model

running on an Apple Macintosh computer. Model variablesentered included: speaker spacing, speaker level, speaker

polarity, speaker delay, head to speaker distance, and headlateral location. All levels are referenced to the

loudspeakers one-meter level. The standard stereo setup of

Fig. 7 is assumed in every simulation.

Several values of head shift were modeled. These values are

noted on each figure. Note that lateral head shifts changeboth the amplitude and frequency characteristics of the comb

filtering at both ears.

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Theoretical Sound Field at Listener's Ears for a Spaced-Speaker Stereo Listening Setup wit_ Central ReflectiveBarrier

Data is shown for the theoretical effects of interaural

crosstalk, on the sound field that exists at the listeners

ear positions, for the standard stereo setu p of Fig. 7, butwith a reflective barrier added along the center line. Both

time and frequency response data is shown.

The data was generated using an Excel spreadsheet model

running on an Apple Macintosh computer. Model variablesentered included: speaker spacing, speaker level, speaker

polarity, speaker delay, head to speaker distance, and headlateral location. All levels are referenced to the

loudspeakers one-meter level.

Three situations were modeled: amplitude panning, delay

panning, and lateral head shift. Note that with the barrierpresent, the signal time arrivals change in lockstep. The

barrier uncouples the crosstalk (and replaces it with a

reflection) and thus makes the delayed signal much more wellbehaved. Compare these responses with the corresponding

responses in Appendices 3, 4, and 5.

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APPENDIX 7

Theoretical Sound Field at Listener's Eats fez a Close

Spaced-Speaker Stereo Listening Setup with CentralReflective Barrier

Data is shown for the theoretical effects of interaural

crosstalk, on the sound field that exists at the listenersear positions, for the standard stereo setup of Fig. 7, but

with a reflective barrier added along the center line, and

the speakers spaced closer together. Both time andfrequency response data is shown.

The data was generated using an Excel spreadsheet model

running on an Apple Macintosh computer. Model variablesentered included: speaker spacing, speaker level, speaker

polarity, speaker delay, head to speaker distance, and headlateral location. All levels are referenced to the

loudspeakers one-meter level.

Two speaker spacings were modeled: 15" apart, and 6" apart

(side by side). At the close spacing, _mplitude panning and

delay panning were modeled. Note thait the frequencies ofthe dips and peaks of the comb filtering go up as thespacing of the speakers is decreased. With the 6" spacing,

the frequency of the first dip in the frequency response is

above the range of human hearing. Spacing the speakersclose together allows the use of a reflective barrier, which

increases the apparent sensitivity and maximum acoustic

output of the loudspeakers by 6 dB.

105

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APPBNDIX 8

Measurement Results for Standard Stereo Setup in Lab

This appendix contains the results of measurements taken on

a standard stereo listening setup, using small loudspeakers.The Radio Shack Realistic Minimus-7 loudspeaker was used forall the measurements. All measurements were taken in a lab

environment with no special treatment to reduce reflections.

Sound Field at Listener's Ears for Normal Spaced-Speaker

Stereo Listening Setup

The loudspeakers were set up in a standard equilateral

triangle with 4 ft (1.22 m) spacing between the speakers andlistener location.

Measurements were made of the sound field that exists at the

listener's location (listener assumed centered). Data was

gathered primarily at the right ear and center head

locations. Both time (0 to 13 msecs) and frequency response(100 to 20 kHz) data was gathered. Three combinations of

speaker on-off configurations were analyzed: 1) left speaker

on only (crosstalk signal), 2) right speaker on only (direct

signal), 3) both speakers on (direct plus crosstalk signals).

Sound Field Measurements with the Use of Wig Head

A wig head was used, in the above setup, to model theeffects of the human head on the interaural crosstalk.

109

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Fig. 84. Frequency response curves taken at the center headand right ear positions (shifted to right 3.375"). Bothmagnitude and phase curves are shown for each condition.(a) Left speaker on only, center of head. (b) Right speakeron only, center of head. (c) Both speakers on, center ofhead. (d) Both speakers on, but out of phase, center ofhead. (e) Left on only, right ear. (f) Right on only,right ear. (g) Left on only, right ear, linear scale. (f)Right on only, right ear, linear scale.

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Fig. 85. Frequency response curves taken at the right earlocation, with both speakers om (direct plus crosstalk

signals). Note the severe comb filtering. The crosstalksignal arrives at 250 usec after the direct sound. Thiscauses comb filtering with dips at 2 kHz, 6 kHz, 10 kHz,etc. (a) Magnitude and phase curves, log scale. (b) Linearscale. (d) Response curve showing the direct effects of thecrosstalk. The curve is a result of taking the dB magnitudedifference between the both-speakers-on condition and theright-on-only condition. Log scale. (d) Linear scale.

!11

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Fig. 86. Time response curves (ETC's) taken at the centerhead and right ear locations for the three possible speakeron-off combinations. (a) Left speaker only, center of head.(b) Right on only, center head. (c) Both on, center head.(d) Right on only, right ear. (e) Left on only, right ear.[f) Both on, right ear.

112

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Fig. 87. Measurements taken, at right ear location, withstyrofoam wig head to simulate presence of human head. Dualsets of magnitude and phase frequency response data wastaken. Log scale on left and linear scale on right. (a)Left speaker on only, log scale. (b) Left on only, linearscale. (c) Right on only, log scale. (d) Right on only,linear scale. (e) Both on, log scale. (f) Both on, linearscale. Even with the wig head present, the comb filteringis still evident, although at a lower amplitude (e), (f).

113

APPENDIX 9

Measurement Results for Recording Studio Control Room

This appendix contains the results of measurements taken inthe control room of a recording studio (Chicago TraxRecording, Chicago, IL). See additional comments in section6.2 (some of which are repeated here).

Measurements of the effects of interaural crosstalk were

made on the loudspeaker monitors in a recently constructedrecording studio control room. Sound field measurementswere made both with and without the presence of a live humanmodel. A sub-minature Knowles microphone was inserted inthe entrance of the ear canal for the live modelmeasurements.

As before, sets of measurements were taken with each monitorspeaker on individually and then both operating. Themeasurements were taken at typical mixing-listening pointsto the rear of the mixing console. Two sets of measurementswere taken: 1) the sound fields at the mixer's ears andcenter head position without the mixer being present and 2)the sound pressure at the mixer's right ear with the mixerpresent at five different locations behind the console. Thesound pressure was measured at the entrance of the mixer'sright ear canal including the effects of head diffraction,head shadowing and pinna transformations [19].

EDITORIAL NOTE AT PRESS TIME (Oct. 21, 1986)

This preprint is getting too largel We are going to includeonly two of the most interesting figures from the completeAppendix 9 measurement set (8 pages of figures removed).Included here, are pinna measurements at the center consoleposition, and console left, which is 20" to the left ofconsole center.

Interested readers desiring the complete set of measurementsshould write or call me at:

Don KeeleTechron, Div. Crown International1718 W. Mishawaka Rd.Elkhart, In 46517

(219) 294-8300

114

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Fig. 88. Measurements of the response at the entrance to theright ea_ canal, for a listener centered behind the console.Both time (ETC, 7 to 27 msecs) and frequency (EFC, 50 Hz to20 kHz) response measurements are shown. (a) ETC, leftspeaker on only (crosstalk signal). {b) EFC, left on only(crosstalk). (c) ETC, both speakers on (direct +crosstalk signals). (d) EFC, both on (direct + crosstalk).(e) ETC, right on only (direct signal). (f) EFC, right ononly (direct). Slight comb filtering is evident in (d) whenboth monitors are on. Refer to Fig. 36 for differencemeasurements for all positions.

115

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Fig. 89. Measurements of the response at the entrance to theright ear canal, for a listener shifted to the left 20" fromconsole center. Both time (ETC, 7 to 27 msecs) andfrequency (EFC, 50 Hz to 20 kHz) response measurements areshown. (a) ETC, left speaker on only (crosstalk signal).(b) EFC, left on only (crosstalk). (c) ETC, both speakerson (direct + crosstalk signals). (d) EFC, both on (direct +crosstalk). (e) ETC, right on only (direct signal). (f)EFC, right on only (direct). Severe comb filtering isevident in {c) and (d) when both speakers are on. Refer toFig. 36 for difference measurements for all positions.

116

APPENDIX lg

Measurement Results for Recommended Barrier Listening Setup

This appendix contains the results of measurements taken onthe split speaker-stand style barrier listening setup. Seeadditional comments in section 6.3 (some of which arerepeated here).

Measurements were made on the split speaker-stand barriersetup to access the following parameters: the amount ofcrosstalk rejection (channel separation), frequencyresponse, energy-time _esponse, and reduction of roomreflections. The Techron TEF System 10/12 was used for allthe measurements. All the raw measurements are displayed inAppendix 10.

In every case the sound field at the listener's ear wasmeasured but with the listener absent. The microphone wasoriented parallel to the barrier and aimed towards thetweeter of the loudspeaker. The microphone was located sothat its diaphragm was 3" (76.2 mm) shifted laterally fromthe barrier and 5" (127.0 mm) to the rear of the barrier.This is the approximate location of a listener's ear ifhe/she were there.

The barrier consisted of a 72" (H) x 30" (D) x 0.75" plywoodboard. The speakers (Minimus-7's) were placed on eitherside of the barrier, with their tweeters against the board.The mic to speaker distance was 30". The speakers were 40"above the floor.

EDITORIAL NOTE AT PRESS TIME (Oct. 21, 1986)

This preprint is getting too large! We are going to includeonly two of the most interesting figures from the completeAppendix 10 measurement set (4 pages of figures removed).Included here the frequency and time curves for the barriersetup.

Interested readers desiring the complete set of measurementsshould write or call me at:

Don Keele

Techron, Div. Crown International1718 W. Mishawaka Rd.

Elkhart, In 46517

(219) 294-8300

117

_lI ._ , . .i-__:,I! i I#1NC I_111I I ! Ill I Ifil I c 1 iiiii I I

1 Ill I IIIIUINIyI. HI IIIII I I

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_!t " ilt

t _1e .Eou[.c N lllll I I _ I I _ Inll I t

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Fig. 90. Frequency responses (both magnitude and phase from100 Hz to 20 kHz) taken on the barrier listening setup. (a)Mic on left, left speaker on only. (b) Mic left, right ononly. (c) Mic left, both on. (d) mic left, both on, out ofphase. (e) Mic right, left on only. (f) Mie right, right ononly. (g) Mic right, both on. (h) Mic right, both on, outof phase. Note the very mild effects of the crosstalk withboth speakers on (c), (g).

118

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tim TIll nih d _ H_6 _ tern TIN[_Nit i .r£c,_5_

(c),i ',[::.:;.;: : ' :lit

. ;,:,;;'.;,,,;, ,;,[;+r, i; i i'

................i -.i!:iii: :i ., . } (

Fig. 91. Time responses (ETC's from 0 to 27 msecs generatedfrom a 200 Hz to 15 kHz sweep) taken on the barrierlistening setup. Note that the vertical top-of-scale SPLvalue changes due to TEF autoscaling. (a) Mic on left, leftspeaker on only. (b) Mic left, right on only. (c) Mic left,both on. (d) mlc left, both on, out of phase. (e) Mic right,left on only. (f) Mic right, right on only. (g) Mic right,both on. (h) Mic right, both on, out of phase. These ETCcurves indicate a crosstalk rejection of about 15 dB (from68 dB down to 53 dB SPL, compare (a) with (b)).

119