Trends and Activities in the Development of Multichannel Sound Systems

GQnther Theile

Institut fiir Rundfunktechnik D-8000 Munich,Germany

The new 3/2-stereo sound format is recommended by specialist groups of CCIR, SMPTE, and EBU. It provides an additional center channel and two surround channels, completing the left and right stereo channels, thereby offering an enlarged listening area and, at the same time, enhanced quality of the stereophonic presentation. This article looks at a number of aspects related to practical applications with and without accompanying picture, and to a final detailed speci- fication of a universal multichannel sound system. Current international discussions and investigations as well as new experiences of the program makers have produced actual results concerning multichannel monitoring in the studio (and home), application of the subwoofer concept and the low-frequency effect channel, downward compatibility, compati- bility with film material, etc. Some of these results may be considered for improvements of the CCIR Recommendation 775, "Multichannel stereophonic sound system with and without accompanying picture," and for the specification of a corresponding universal multichannel Ixansmissionsystem.

1, Introduction to digital sound broadcasting (e.g. DAB) of a classical music concert,without accompanying picture. But also Since many years it has already been widely recognized during the television transmission of the concert the that the conventional two-channel stereophonic loud- viewer/listener will expect the optimum stereophonic speaker technique has serious limitations and that further quality, not the least because when listening to music at developments of loudspeaker stereophony are desirable home there may be frequently a strong desire to close with regard to providing an improved stereophonic image one's eyes and concentrate on the auditory event, thereby for a number of listeners who are not positioned at the avoiding the distraction of a more or less appropriate ideal reference point.of the loudspeaker arrangement (e.g. picture. /1/.../7/). During thc last years a great deal of investiga- tive and development work has taken place throughout Considering this basic compatibility requirement, CCIR the world initially addressing the standardization of a TG 10/I and specialist groups of SMPTE and EBU/22/, suitable multi-channel stereophonic system to accompany /23/, /24/ recently have recommended one additional high-definition television (e. g./8/.../20/). However, it center channel C and two side/rear surround channels Ls, has become clear very soon that the improved presenta- Rs, completing the conventional left/right stereo tion performance is desirable not only for applications channels L, R. This new reference format is refered to as with accompanying picture but also in case of audio-only "3/2-stereo" (3 front / 2 surround channels). It is specified applications/5/,/9/,/13/,/14/,/20/,/21/, in CCIR Recommendation 775 /22/ "Multi-channel stereophonic sound system with and without accom- We may envisage that in a few years the television set panying picture", within a hierarchy of sound formats will be replaced by a "home movie" system which will providing lower numbers of channels and reduced include a relatively expensive multi-channel sound stereophonic presentation performance. Possible alter- reproduction system in addition to the picture display. It native lower level sound formats are 3/1, 3/0, 2/2, 2/1, will be able to overcome some of the weakness of 2/0, 1/0 which may be used in circumstances where conventional two-channel stereophonic systems. Further- economical or channel capacity constraints apply in the more, in the domestic environment there will unlikely be transmission link or where only a lower number of acceptance of, or space for, both the special loudspeaker reproduction channels is desired. arrangement for audio-only reproduction and the special loudspeaker arrangement for television sound, side-by-side In principal, the 3/2- or 3/4-loudspeaker arrangement in the home. offersenhanceddirectionalstabilityand clarity of the frontal sound image and improved realism of auditory CCIR Task Group 10/1 (multi-channel sound systems) ambience. Basic characteristics and considerations of the was therefore faced with the problem of defining a new five-channel stereophonic format have already been universal loudspeaker repro-duction standard which is able discussed in previous papers (e.g. / 17/, / 18/, / 19/).Those to satisfy the requirements of HDTV sound whilst also aspects related to the specification of a corresponding providing optimum stereophonic quality to satisfy the universal multi-channel transmission system are "purist" music-lover when, for example, he is listening presented elsewhere (e.g./26/,/27/).

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This article looks at a number of aspects related to location of the listener and important for let's say 90 % practical applications with and without accompanying of the dialogue. It is also well-known that the perceived picture, and to a final detailed specification of a universal quality of a centre phantom image (e.g. speaker) is multi-channel sound system. Current international unfavourable with respect to sound colour, "clarity" and discussions and investigations as well as new experiences spatial sharpness when compared with a corresponding of the programme makers have produced actual results centre loudspeaker image /17/,/28/. concerning multi-channel monitoring in the studio (and home), application of the subwoofer concept and the low frequency effect channel, microphone and sound mixing Compatibility with film sound techniques, downward mixing, compatibility matrixing, compatibility with film sound material etc. Some of Another important advantage is related to the compati- these results may be considered for improvements of bility with film sound material. Looking at the common CCIR Recommendation 775, and for the specification of practice in the cinema (resulting from developments for a corresponding universal multi-channel transmission several decades), adequate directional coincidence of system, auditoryand visualeventsis achievedhere by three screen-related loudspeakers (Fig. l, top). L C R 2. Three front channels J=K nj=,,, jml,

It has been shown in previous papers/13/,/14/that the directional stability of the frontal image increases W _ _ disproportionatelyOirectiowith nathelstaincreasebility in the number of the ILCI-"' NEMASCREEN ] front loudspeakers. The listening area ensuring suffi- ciently small directional imaging distortion is about three C times wider and deeper when four front loudspeakers are L yn, R used instead of three. Thus, if absolute image location is important, a four-front-loudspeaker arrangement is better HDTV SCREEN [.a_ than a three-front loudspeaker arrangement which is itself better than conventional 2/0-stereo. W

However, the three-front-loudspeaker arrangement has I-" B _ i been identified to be the optimum compromise, due to B ' W = 1,2 several considerations presented below: Fig. l: Comparison of three-front-loudspeaker As regards audio-with-picture reproduction, it is reaso- arrangementsfor sound accompanying nable to consider not the listener's perceptibility threshold cinema and domestic HDTVpresoztations to directional imaging distortions (i. e. to directional discongrnity of auditory and visual events as investigated This cinema situation will not differ significantly from e.g. in/10/), but rather his tolerance threshold (i.e. the the future domestic HDTV situation, when we consider acceptable directional imaging distortion). The acceptable further developments of television displays: It is expected extent of angular displacement between visual and audi- that future displays (e.g. home projection systems) will tory images has been investigated using normal pro- lead to large screens (1.5...3 meters wide) and to corres- gramme material. Account was therefore taken of ponding viewing angles much greater than 33°, because distractions caused by the spectator's interest in the the high picture quality of HDTV allows "telepresence", programme content, the association of the visual and similar to that enjoyed in the cinema, as shown in Fig.1 auditory images ("perceptual fusion" phenomenon), the (below). It seems realistic and advantageous to consider width of the sound source and, last not least, the type of simply almost congruity of the listening angle and the programme material. It was concluded from the results of viewing angle for the specification of the reference HDTV corresponding experiments published in /11/ that the sound/picturedisplay arrangement. directional displacement should be less than 15° (tolerance threshold). This means that the directional stability For the production standard and domestic HDTV presen- provided by three loudspeakers is tolerable. Practical tations it is proposed to specify the relation listening experience of several recording teams in different studios angle / viewing angle ("congruity index" ci = B .W). The and with widely differing types of programme confirms this conclusion, congruityindex should be approximatelyci _ 1.2. For instance, a listening angle of 60 ° would imply a viewing Particularly in the case of andio-with-picture presentation angle of about 50°. the most dominant benefit from the center loudspeaker is obviously the "stable middle", which is ensured at any

AES12thINTERNATIONALCONFERENCE 181 THEILE ' :=

It is clear that a congruity index ci = 1.2 is not benefifial DEr rY.3 when a large screen is undesired or a relatively small I . :- .{ HDTV monitor display must be used instead of the larger [_ so 'i !..?.:51..i.;:""_:_':i. flat HDTV (projection) display. However, these cases should be considered as non-conform with the HDTV ,D } .i.:z::_:';. reference arrangement, although they represent the normal _0 situation of today. The proposed specification ci _ 1.2 ....i.i.ii...... 5':ii?'"'i"': ".iZ.i.Z;.... i.Z...... ;:':

picture combined with adequate high-quality sound ¢ J0' : ?..._;'Z'ii'i'i'i .. ' reflects the basic intention of a large high-definition 2o }i : }i' i'!i"!i':':iI":"Z:ii'i: today, and which will be used in the home tomorrow. ;"_i '5 Iii 'rl!i'"-..-[ -t0t'' _' _ £_- · .._i ! aL [eiB] presentation, which should be the standard in the studio _ i_t3.___ _it_: i _ i {'_I .....i ...i t}t..'

fight loudspeaker beside the screen. Furthermore, it would 'i..?'i'::!.I.' Specificati°n °f ci_ 1'2 w°uld °ffera practical reali- _ :::_:iiI:z'II.;?:: i( I_ :'" respeensurect tosatisfyingthe sound/cinemapicture-congruity./HDTV compatibilityThe sound/picturewith .." ' congruity performance is nearly as high as in the cinema. Ri This is by the factor of about two higher when compared with the initial situation (viewing distance 3H, viewing angle 33°), because three screen-related loudspeakers are available/14/. Fig. 2: Perceived directions lm in front of the referencepoint of the three-front-loudspeaker arrange-ment Limited depth of the listening area (B = 3m) as a function of panpot level differences/29/.

When we look at audio-only applications, or for example This will necessitate the introduction of an additional the television transmission of a classical music concert, delay for the center loudspeaker, as illustrated in Fig. 3. directional mismatch of picture and sound sources is not It is easy to see that the compensation delay At depends morethe problem.annoyingRather,than fordirectionalthe film distortionsound: In maythis cabeseeventhe on the width B of the loudspeaker basis. In the case where stereophonic quality is the dominant evaluation factor. In B = 3m, At equals about 1.2ms. If, this compensation particular, directional stability is particularly desirable, in delay is not introduced the phantom sound sources will order to avoid direc-tional concentration and displacements displaced towards the centre, even more than plotted in of, for example, the music instruments of an orchestra. Fig. 2.

However, for these pure stereophony applications a /

characteristic of the three-front-loudspeaker arrangement is t C particularlylistener fromd isthead vreferencean te geous:pointDis placementsin the center-lineof the L '__"_"_:-_ R produces imaging distortion, in contrast to the two- loudspeaker arrangement, due to the symmetrical situa- tion. If the listener moves forward along the centre-line, e.g. lm, he will receive the direct sound from the centre loudspeaker about 600 _usearlier than that from the left or right loudspeaker.The phantomsoundsourceoriginally x / sharply localizable under -15 ° or +15 ° is displaced close /it = B[m] · 0,39 ms to the center, while involving together a decrease of sound quality. Fig. 3: Delay Atfor the centre signal if the In Fig. 2 the corresponding localization curve is plotted loudspeakers are arranged in a straight line. (details are presented in/29/). The source is panned across

ltheocalizatithreeonfrontcurveloudsispeakerslinear L,at Cthe, R inreferencea way thatpoint.the On the other hand, looking at the three-front-loudspeaker Obviously the same effect oecurs if the front loudspeakers arrangement for cinemas (Fig. I, top)., the compen- sating delay would principally result in incompatibility alareongsettheupwallnot oinf thea cirlisteningcle, butroom.rather in a straight line with this respect. However, this concern has no practical relevance because in most cases film sound material is uncritical regarding directional stability (phantom sound sources are avoided in the sound mix).

182 AES12thINTERNATIONALCONFERENCE TRENDSANDACTIVITIESINTHEDEVELOPMENTOFMULTICHANNELSOUNDSYSTEMS

Center loudspeaker behind the screen It is concluded that the location CO of the center loud- speaker should be recommended for the reference loud- A further consideration is related to the height of the front speaker arrangement, implying further development of loudspeakers, in particular of the center loudspeaker in suitable HDTV picture display as for example the cases where the HDTV-display is provided as illustrated projection technique in combination with acoustcally in Fig. 4. transparent projection screens. HDTV should ensure an optimum balanced presentation quality of both, picture and sound ! L R

fl C°_ '_E_ - 3 Side/rear surround channels The addition of two side/rear surround channels to the

C--/ ambience. The sound mixing staff can add an acoustic =_j/_ thenvironmentree front channelsto the frontalallows stereophonicimproved realismpresentationof auditoandry tailore for a variety of purposes, for example, to achieve Fig.4: Proposed location Co of the center loudspeaker, natural three-dimensional spatial impression, to generate behind the screen a new artificial room, or to create realistic ambience (applause, rain-, wind-, traffic-noise) or special side/rear Experience with both arrangements, center loudspeaker directional effects. located either beneath (location C1) or behind (location CO) the (acoustically transparent) screen has shown that However, the addition of side/rear surround loudspeakers there results a surprisingly high benefit from the pro- does not enlarge the listening angle (by delivering vision of height congruity. The discrepancies perceived in genuine surround localization of phantom sources). Thus, location C1 for picture related sound sources can be in contrast to Quadrophony, the locations of the side/rear annoying, particularly if small sized center sources are surround loudspeakers are largely noncritical with respect displayed, which may even be located in the upper region to both direction and distance, and they can be placed to of thescreen, fit intoan existingliving-roomenvironment.

In practical large-screen-situations, where we expect Optionally, the two surround signals may be reproduced viewing distances 2...2,5 times of the picture height, the via an even number of more than two rear/side surround directional displacement in the median plane is about - loudspeakers. It is a well-known technique for cinema 20°...- 25°. This is more than in the horizontal plane and sound to provide delocalization for the surround sound is not tolerated in many occasions of normal programme since there is no supporting picture, and since many material, although the listener is less critical in the surround effects are meant to be enveloping and thus not median plane than in the horizontal plane, localizable by definition / 16/. This is achieved by en- hancing the number of surround loudspeakers, by using When we consider sound presentation which is mainly loudspeakers which minimize the direct sound, and by non-picture-related such as music or which is not introducing suitabledecorrelation of thesurround signals accompanying a picture, the "negative elevation" (e.g. delay). Experience with HDTV sound presentations produced by the arrangement L / C! / R is perceived as a has shown that one additional pair of side/rear.surround deformation of the horizontal imaging plane, more loudspeakers and the provision of appropriate delay annoying than the ("positive") slight elevation arising in ensures a significant enlargement of the optimum conventional two-channel stereophony/31/, listening area and greater envelopment.

There seems to be no other solution than using the Therefore, a3/4-1oudspeakerarrangement is recommended arrangement L / CO / R if optimum presentation by CCIR and EBU /22/, /24/, particularly for collective performance is desired. Compensation techniques listening situations (auditorium about 5...25 persons). applicable to the arrangement L / C1 / R which do realy work without reducing the sound quality are not known. It is clear that the number of surround loudspeakers must Neither the exploitation of the "directional bands"/31/ not necessarily equal the number of surround signals. One nor any kind of phantom sound source (e.g. between or two surround signals may feed two or four (or more in center loudspeakers above and beneath the screen) will the cinema) side/rear loudspeakers. However, as regards ensure the desired performance regarding sound colour, the number of surround channels, the reference production "clarity", and spatial sharpness, and transmission format will be limited to 3/2-stereo, for a number of important practical and economical reasons. This is in accordance with the digital film sound format where a larger number of side/rear loudspeakers is fed with only two surround signals.

AES12_hINTERNATIONACOLNFERENCE 183 THEILE

Universal 312-stereo transmission format 'applause' Accordingly. it is proposed to delete the general provision 2-Channel-Surround 4-Channel-Surround of four surround signals in CCIR Recommendation 775 1-Channel-Surr0und 2-Channel-Surr0und /22/. and to recommend only a 3/4-stereo reproduction 1-Channel-Surround 4-Channel-Surround system, thereby excluding storaging and transmission of 'atm0' 3/4-stereo signals, but including the possibility to use 2-Channel-Surround : 4-Channet-Surr0und upwards-conversion techniques for 3/4-monitoring of 3/2- 1-Channel-Surr0und _ -, 2-Channel-Surround stereo programme material. This restriction is suggested 1-Channel-Surr0und 4-Channel-Surr0und to be a reasonable compromise, due to a number of .- 'music' significant aspects: 2-Chanrlel-Surround 4-Channel-Surround 1-Channel-Surround 2-Channel-Surround - Economical constraints in the production studios (broadcasting houses, recording industry, film 1-Channel-Surr0und 4-Channel-Surr0und industry) do not allow the maximumpefformance -3 -2 -' 0 +1 +2 +3 level.

- It has been recognized that the specification of Fig. 5: Preference between 1-, 2-, and 4-channel down-conversion equations (from 3/4-stereo into surroundsound. Plotted are median value the 3/2- or 3/0-stereo format) is particular and interquartilerange. problematic.

- For different reasons the capacity of future trans- It should be considered that the slight superiority of the mission systems and recording media, in particular four-channel surround sound over two-channel surround DAB®, DTTB, HD-MAC, PALplus, ATV, CD-I sound would be further reduced by using suitable decorre- is too small, lation techniques /7/, /13/, /17/. Experience of pro- gramme makers in different situations and primary results In order to allow applications as universal as of running investigations on the evaluation of decorre- possible, the future ISO multi-channel sound lation techniques confirm that for imaging of spatial coding standard will provide only five main service impression ("music", Fig. 5) the superiority can be channels/27/, compensated almost completely by means of appropriate delay. The superiority of the 3/4-stereo format according to/22/is remarkable only in some occasions, It is clear that a variable delay time is benefitial in order when compared with the 3/4-presentation of 3/2- to match the recorded room situation. As proposed earlier signals/14/,/19/,/30/ . fl3/, it may be worthwhile to develope and specify a studio controlled decorrelator / room simulator, which The last point shall be explained more detailed. A could generate satisfying secondary surround signals in relevant experiment on this subject has been reported in the receiver from the received signals at negligible cost. /30/. A 2/4-loudspeaker arrangement was used for any On the other hand, reverberation and also delay will presentation, however, the format of the surround signals obviously be less helpful when we consider presentation was either mono, two-channel stereo, or four-channel of the auditory environment ("applause", "atmo", stereo. The four-channel stereo surround signal was Fig.5). In that case there is the need of additional direct derived from room microphones.The stereo and mono sound contributing to the ambient floor of non- surround signals were generated by downward conversion localizable sources. The situation is even aggravated in /14/,/29/and allocated to the four side/rear loudspeakers cases where additional localizable sources in the area without introducing any kind of decorrelation technique, behind the listener (directional off-effects) are desired. Listeners were asked to indicate their preference regarding Further developments may improve the possibilities of "realism of concert hall atmosphere" by means of the proces-sing satisfying secondary surround signals even for CCIRseven-gradescale, thesetypesof surroundsound.

Considering this, we may conclude that the standard- Results of A-B-A-B comparative tests are shown in ization of a 3/4-stereo production and transmission format Fig.5. They show that the improvement achieved by is dispensable.- the second pair of surround signals is less significant when compared with the step from one-channel to two- channel surround, and that imaging of spatial impression ("music") is less critical than auditory environment ("applause", "atmo").

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312-stereo reference loudspeaker arrangement This placement area for the surround loudspeakers appears to be a good compromise. It includes almost lateral A further aspect is related to the location of the side/rear directions (_+100°). This seems reasonable for practical surround loudspeakers. CCIR Recommendation 775 does reasons: Inquiry results (about 100 german house-holds) not specify precise locations, rather, different placements have shown that more than 50% of the living room of the surround loudspeakers are possible to fit into an environments do not allow placements of Ls/Rs behind existing control-room, or living-room environment. In the listener, because there is the wall. particular, the possible directional range of the surround loudspeakers.in the 3/2-arrangement according to CCIR Regarding the surround sound quality there is no Recommendation 775 is _+60°...._+120°. generally applicable answere on the optimum placement of the surround loudspeakers. A number of experimental The assumption is that the locations of the surround results indicate that a more lateral placement may be loudspeakers ar_ largely noncritical, because genuine optimum for most types of surround sound, in particular surround localization of phantom sources is not required, indirect sound (imaging of space, e.g. "music") /7/, / 13/, and only the addition of an acoustic environment to the /3 I/,/32/, but also non-localizable direct sound (imaging frontal image is intended. However, it is clear that these of ambience, e.g. "applause","atmo") / 13/. However, acoustic environments will be effected more or less by other investigations on this subject show that a more rear the locations of the surround loudspeakers, depending on location appears to be optimum/35/,/36/. It is suggested the type of surround sound. This may be tolerated to a that the result depends strongly on the programme certain degree. However, investigations and current material. experience of recording teams have proven that a more precise specification is necessary, particularly in the 3/2- arrangement: basic differences of the surround sound presentation result, if the loudspeakers are moved from 4. Subwoofer channel about +120 ° to about -+90° or even _+60°. In other words, if the sound is balanced by means of a -+120°-arrange - At the reproduction side the socalled subwoofer channel ment, the intended auditory event will often be changed in may be used. It is capable of handling signals in the the _+90°- or -+60°-arrangement to an unacceptable extend, range 20 Hz to 120 Hz and includes the information of two low frequency channels: A more precise location of the surround loudspeakers - Low frequency effect channel (LFE) should be specified as the reference arrangement. In - Low frequency main channel (LFM) particular, it is proposed /33/ to use about -+100 °.... In Fig. 7 the principal difference of both channels is ·+120°for the loudspeakers Ls/Rs in the 3/2-format. The illustrated. proposed arrangement is illustrated in Fig. 6.

B _ L' ' _ R' L R _ O' Ls' ,,,.,. ,,., 't_ i 1' /' '-, '., _ i' / /;/ pr"'"'- RS'

·., , . _' y Y /..'""....'" .. Subw. loo- L F E

120 °

LS RS Fig. 7.' Low frequency effect (LFE) and lowfrequeny main (LFM) channel

Low frequency effect channel

Fig. 6: Proposed 3/2-stereo reference The purpose of this channel is to eable litseners, to loudspeaker arrangement itt HDTVapplication extend the low frequency contend of the reproduced Screen 1: Reference distance 3H (2fi l = 33 °) programme in terms of both frequency and level. In this Screen 2: Proposed distance 2H (2fi 2 = 48 °) way it is the same as used for digital film sound systems. (Copy from/33/) It carries high level, low frequency sound effects which

AES12aIhNTERNATIONCONFERENCEAL 185 THEILE

are intended to be fed to a specific subwoofer loudspeaker. References In that way the magnitude of the low frequency content of the main channels is restricted so that the main loud- speakers are not required to handle these special effect /1/ Keibs, L.: "M6glichkeiten der Stereo-Ambio- signals, fonen Schalliibertragung auf 2 Kan'alen". (Possibilities for transmitting sound by stereo-ambiophony over two The low frequency effect channel is not used for the entire channels). Acustica, 1962, pp. 118-124 low frequency content of the multi-channel sound presentation. It is an option, at the reproduction side, and /2/ Gerzon, M.A.: "Experimental tetrahedral thus carries only the additional LEE information. The recording". Studio Sound, Aug., Sept., Oct. 1971 main channels carry normal low frequency sounds, and they are sufficient on their own if the effects are not /3/ Condamines, R.: "Microphone a n d desired by the user. loudspeaker arrangements for tetraphony". EBU Review No. 143, Febr. 1974, pp. 12- 18

Low frequency main channel /4/ Lauterslager, H.; Nuyten, P.: "Ambience- related transmission systern (ARTS)".J. Audio Eng. Soc. Low-frequency mono reproduction of the main signals by (25), 1977, pp. 29 - 34 means of a common subwoofer system is obviously particularly advantageous for multi-channel sound /5/ Scherer, P.: "Ein nenes Verfahren der applications, because the size of the main loudspeakers raumbezogcnen Stereophonic mit verbesserter Ubcr- can bc reduced, and the design can be optimized. An tragung der Rauminformation". (A new method of room increase of the low- frequency cutoff from, for example, related stercophony with improved transmission of room 30 Hz to 120 Hz reduces the constraints in terms of information). Rundfunkt. Mitt., 1977, pp. 196 - 204 required net-volume and weight, choice of transducer principle etc. dramatically. The volume could decrease /6/ Steinke, G.: "Entwicklungstendenzen der approximately 90%, and important electro-acoustical Stercofonie". (Development tendencies of stereophony). parameters such as impulse response and directivity-index 13. Tonmeistertagung 1984, Miinchen, Conf. minutes could be optimized with less compromises, pp. 137 - 157

Thus, five fullrange loudspeakers having identical low- /7/ Griesinger, D.: "Theory and Design of a frequency sound pressure level performance would require Digital Audio Signal Processor for Home Usc". J. Audio an overall net-volume significantly higher (factor 2.5) Eng. Soc. 37, 1989, pp. 40 - 50 compared with a corresponding subwoofer system. Small stereo loudspeakers in the 3/2-arrangement and flexible /8/ Thomas, M.; P!enge, G.: "Probleme der placement of the common subwoofer(s) allow bildbezogenen Tondarstellung bei HDTV-GroBbild- aesthetically acceptable solutions in the living room. wiedergabe". (Problems of picture related sound presen- tation in HDTV large-picture reproduction). 14. Ton- In a recent study on this subwoofer concept/34/it was meistcrtg. M'dnchcn, 1986, Conf. minutes pp. 338 -350 concluded that it is even possible to improve the loud- speaker response within the listening area by using a /9/ Ohgushi, K.; Komiyama, S.; Kurozumi, separate low-frequency loudspeaker, which is located due K.; Morita, A.; Ujihara, J.: "Subjective evaluation to optimum low-frequency response rather than optimum of multichannel stereophony for HDTV". IEEE stereophonic presentation. Studies on the effects of Transactions on Broadcasting (33), 1987, pp. 197 - 202 standing waves in a room demonstrate that it is advan- ageous to optimize the loudspeaker placement with /10/ Theile, G.: "Wie natiirlich kann das stereofone respect to low-frequency performance, in particular sound Klangbild in Zukunft sein?" 15. Tonmcistertagung pressure distribution and low-frequency cutoff point 1988, Mainz, Conf. minutes pp. 78- 105 ("placement eqtmlization"). /11/ Komiyuma, S.: "Subjective Evaluation of There is some evidence that the subwoofei system in fact Angular Displacement between Picture and Sound could improve not only the acceptance of multi-channel Directions for HDTV sound systems". J. Audio Eng. loudspeaker arrangements but also the performance of Soc. 37, 1989, pp. 210 - 214 loudspeaker reproduction in the home and even in the studio. /12/ Miyasaka, E.; Takegahara, T.: "3-1 Quadraphonic sound reproduction system and transmission system for HDTV". 131st SMPTE Techn. Conference, 1989, preprint No. 131-164.

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/13/ Theile, G.: "The natural rendering of sound /25/ CCIR Task Group 10-1: "Input from CCIR images in broadcasting". EBU Review Nos. 241 - 242, to ISO MPEG Audio Group". Temp. Document 9. 1990, pp. 95 -116 October 1992, Geneva

/14/ Theile, G.: "HDTV sound systems: how many channels?" AES 9th Intern. Conference, Detroit, Febr. /26/ Theile, G.; Stoll, G.: "MUSICAM- 1990, Conf. minutes pp. 217 - 232, and AES 10th Surround: The Universal Multi-Channel Coding Intern. Conference, London, Sept. 1991, Conf. minutes System". 17.Tonmeistertagung Karlsruhe, 1992, pp. 147 - 162 conference minutes pp 96 - 108

/15/ Theile, G.: "Further Developments of Loud- /27/ ISO/MPEG-Audio: "ISO 11172-3 Compatible speaker Stereophony". 89th AES Convention, 1990, Low Bit-Rate Multi-Channel Audio Coding System". preprint No. 2947 First Working Draft, ISO/IEC JTC1/SC29/WGll N0403, MPEG 93/479, April 1993 /16/ Steinke, G.: "Von der Ambiophonie zur HDTV-Heimbeschallung". 16. Tonmeistertagung, Karls- ruhe, 1990, Conf. minutes pp. 137 - 157. ("From /28/ Silzle, A.; Theile, G.: "HDTV- Ambiophony to HDTV Home Sound Reproduction", Mehrkanalton: Untersuchungen zur Abbildungsqualit_t CCIR Doc. IWP 10/12-24, 1990). beim Einsatz zus_itzlicher Mittenlautsprecher". (HDTV multi-channel sound: Experiments on the imaging quality /17/ Holman, T.: "New Factors in Sound for by using additional center loudspeakers). Cinema and Television". J. Audio Eng. Soc. (39), 1991, 16.Tonmeistertagung Karlsruhe, 1990, conference pp.529-539 minutespp.208- 218 /18/ Meares, D.: "High-quality sound for high definition television". AES 10th Intern. Conference, /29/ Rebscher, R.; Theile, G.: "Enlarging the London, Sept. 1991, Conf. minutes pp. 163- 177 Listening Area by Increasing the Number Loudspeakers". 88th AES Convention, 1990, preprint No. 2932 /19/ Meares, D., Theile, G.: "High-quality sound for high-definition television". In: EBU-Satellite /30/ Roth, S.; Kriimer, U.; Theile, G.: broadcasting of digital HDTV. Publ. by the EBU, 1992, "HDTV-Mehrkanalton: Surround-Signale zur Darstellung pp. 65 - 78 der Konzertsaal-Atmosph'are". (FtDTV multi-channel sound: Surround signals for imaging the concert-hall /20/ Gerzon, M.: "Three Channels for the Future of atmosphere). 16.Tonmeistertagung, Karlsruhe, 1990, Stereo?" Studio Sound, June 1990, pp. 112 - 125 conference minutes pp. 190 - 207

/21/ Theile, G.: "Surround Sound: A new Opportunity for Radio". NAB/Radio Montreux Intern /31/ B!auert, J.: "Spatial Hearing The Symposium, June 1992 Psychophysics of Human Sound Localization." The MIT- Press, Cambridge, Mass.; 1983, ISBN 0-262-02190-0 /22/ CCIR Recommendation 775: "Multi- channel stereophonic sound system with and without /32/ Barton, M.; Marshall, H.A.: "Spatial accompanying picture", 1992. Impression Due to Early Lateral Reflections in Concert Halls". J. Sound Vibr. 77, 1981, pp. 211-232 /23/ SMPTE Film Sound Sub-Committee Report: "Proposed Recommended Practice: Loudspeaker /33/ CCIR TG 10/1: "Multi-Channel Sound ElectrPlacementsonic forProductiAudion".MonitoDringocumentin HighN15.04Definiti7152,on System: Positioning of Surround Loudspeaker" Doc 10- December 1991 1/Temp/4, March 1993

/24/ EBU - V3/HTS Draft Report: "A possible /34/ Kiigler, C.; Theile, G.: "Loudspeaker world standard for multi-channel sound" Document GT Reproduction: Study on the Subwoofer Concept". 92nd V3 1303, January 1992 AES Convention, March 1992, Preprint No. 3335.

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