1、Rec. ITU-R BS.1286 1RECOMMENDATION ITU-R BS.1286METHODS FOR THE SUBJECTIVE ASSESSMENT OF AUDIO SYSTEMSWITH ACCOMPANYING PICTURE(Question ITU-R 106/10)(1997)Rec. ITU-R BS.1286The ITU Radiocommunication Assembly,consideringa) that Recommendations ITU-R BS.1284, ITU-R BS.1116, ITU-R BT.710 and ITU-R BT
2、.500 have establishedmethods for assessing the subjective quality of audio and video systems respectively;b) that Recommendation ITU-R BS.775 specifies one universal multichannel stereophonic sound system with andwithout accompanying pictures;c) that perceptual interaction between sound and picture
3、can affect the assessment of sound quality;d) that existing methods for subjective assessment of sound quality are sometimes inadequate for sound systemswith accompanying pictures;e) that the use of standardized methods is important for the comparison, exchange, compatibility and correctinterpretati
4、on of data, derived from subjective tests carried out at different times and/or places,recommends1 that the testing and evaluation procedures given in Annex 1 be used for the subjective assessment of soundsystems with an accompanying picture.ANNEX 11 GeneralThis Annex is divided into the following s
5、ections, giving detailed requirements for various aspects of the tests:1 General2 Experimental design3 Selection of the listening panel4 Test method5 Attributes6 Programme material7 Reproduction conditions8 Statistical analysis and presentation of results.Sound and picture are inseparably combined i
6、n TV and movie programmes. Under normal circumstances, the observersshould perceive the sound and picture with a sense of unity. Therefore, the presentation of pictures may be indispensablefor some subjective assessment of sound quality.Visual stimuli often affect the perception of sound. For exampl
7、e, the apparent direction of a sound image is frequentlyshifted to that of the corresponding picture, which is well-known as the “ventriloquism effect”. Also, visual stimulisometimes make aural impairments less noticeable.2 Rec. ITU-R BS.1286The following fields of assessment require the presentatio
8、n of a visual image: correlation between picture and sound images; basic audio quality as influenced by the presence of a visual image; harmony of spatial impressions of picture and sound; assessment of listening and viewing arrangements.2 Experimental designIn designing the tests, the consideration
9、s of Recommendation ITU-R BS.1116, 2, should be taken into account. Theuse of a reference is not always necessary.3 Selection of the listening panelFor the selection of the listening panel, the considerations of Recommendation ITU-R BS.1284 should be taken intoaccount. In cases where the impairments
10、 are small, the considerations of Recommendation ITU-R BS.1116, 3, shouldalso be taken into account.4 Test methodTo conduct subjective assessments with an accompanying picture, it is necessary to select appropriate methods.If the subjective differences are expected to be small it is appropriate to u
11、se the double blind triple stimulus with hiddenreference method as described in Recommendation ITU-R BS.1116, 4.If the subjective differences are not small and it is appropriate to use less sensitive methods than those of Recommen-dation ITU-R BS.1116, the test methods of Recommendation ITU-R BS.128
12、4 should be used.It should be noted that the reference signal need not be unimpaired in an absolute sense.Subjects should be instructed to assess the sound quality in association with the video presentation, rather than to assessthe sound quality alone.It should be noted that the five-interval scale
13、 used for video assessment in Recommendation ITU-R BT.500 differsfundamentally from the five-point scales of ITU-R BS.1116 and ITU-R BS.1284.5 AttributesThe following attributes may be assessed: Front image quality: for definition see Recommendation ITU-R BS.1116, 5.3. Impression of surround quality
14、: for definition see Recommendation ITU-R BS.1116, 5.3. Basic audio quality: for definition see Recommendation ITU-R BS.1284, 5.1. Correlation between sound and picture images.The last attribute may include the following characteristics: correlation of source positions derived from visual and audibl
15、e cues (including azimuth, elevation and depth); correlation of spatial impressions between sound and picture; time relationship between audio and video.Rec. ITU-R BS.1286 36 Programme materialThe test programme material should be selected to stimulate the attributes of interest. Different attribute
16、s may needdifferent types of test programme.In general, the aspects described in Recommendation ITU-R BS.1116, 6, are also valid for sound with accompanyingpicture.The time difference between sound and picture may be one of the parameters to be assessed. If it is not, then it should bemade as small
17、as possible. In some cases it may be necessary to correct the relative delays of the audio and video signals.NOTE 1 The permissible time difference between sound and picture is currently defined in Recommen-dation ITU-R BT.1359.7 Reproduction conditions7.1 AudioUnless they are included in the attrib
18、utes under test, the following parameters should conform to Recommen-dation ITU-R BS.1284 or Recommendation ITU-R BS.1116, 7 and 8: Reference monitor loudspeakers or headphones Reference listening room Reference sound field conditions Reverberation time Operational room response Listening level List
19、ening arrangements Listening position Loudspeaker base width Background noise level an effort should be made to minimize the masking effect due to room noise andreproduction device noise. The total noise level, with technical equipment, should not exceed NR30.7.2 VideoA number of ITU-R Recommendatio
20、ns exist for the relationships between picture size and viewing distance as well asloudspeaker base width and listening distance. In general, these are mutually incompatible. Therefore compromises mustbe made in either audio or video arrangements to permit both listening and viewing to be carried ou
21、t simultaneously.Which Recommendations take priority will depend upon the objectives of the test. For the assessment of audioattributes, the considerations of Recommendation ITU-R BS.1116 should take priority.The following considerations should be taken into account when selecting viewing conditions
22、 and the size of the videodisplay device: Display size and viewing conditions for assessing different TV systems are given in a number of ITU-R Recom-mendations (see Table 1 of Appendix 1). The viewing distance should be similar to the listening distance, though ITU-R gives no recommendations about
23、thecombined arrangement of loudspeakers and display device. The recommended loudspeaker base width and listening distance for assessing audio systems are given in Recom-mendation ITU-R BS.1116 (see Table 2 of Appendix 1).Figures 1 and 2 show the relationship between loudspeaker base widths and displ
24、ay sizes for two aspect ratios accordingto the considerations mentioned above. These figures indicate the problems which might occur if fixed viewing distanceswere to be recommended.The choice of display size is limited; for example, with a base width of 3 m, an aspect ratio of 16:9 and a viewingdis
25、tance of 3 H, the maximum permitted display size is 70 in.4 Rec. ITU-R BS.12861286-013 H4 H6 H3214500204060 80 100 120 140CRLBasewidth (m)Case ACase BScreenBase width: 2-5 mViewing distance: 3 H-6 HBase angle: 60FIGURE 1Relationship between the loudspeaker base width and the videodisplay screen size
26、 for a 16:9 aspect radioCase BCase ASize of display (in)Basewidth (m)FIGURE 1/BS.1286 = 17 CMThe choice of viewing distance is limited. For displays with built-in loudspeakers the base width and display heightare fixed. If the base width was 2 m and the display size 28 in, the viewing distance would
27、 necessarily be 4 H for a4:3 aspect ratio display.The viewing distance, therefore, cannot be rigidly fixed and can only be recommended with some degree of flexibility.The recommended ranges of viewing distance are 3 H to 4 H for high definition television (HDTV) and 4 H to 6 H forconventional TV sys
28、tems.Rec. ITU-R BS.1286 51286-02LCR3214500204060 80 100 120 1403 H4 H6 HSize of display (in)Basewidth (m)Case ACase BScreenBase width: 2-5 mViewing distance: 3 H-6 HBase angle: 60FIGURE 2Relationship between the loudspeaker base width and the video display screen size for a 4:3 aspect ratioCase ACas
29、e BFIGURE 2/BS.1286 = 17 CM8 Statistical analysis and presentation of resultsThe analysis of the experimental data and the method of presentation of the results should conform to RecommendationITU-R BS.1284 or ITU-R BS.1116, 9, 10 and 11 as appropriate.6 Rec. ITU-R BS.1286APPENDIX 1TO ANNEX 1TABLE 1
30、Viewing distance and display size recommended in ITU-R RecommendationsTABLE 2Listening distance and base width recommended in Recommendation ITU-R BS.1116System type Viewing distance and display sizeITU-RRecommendationsMonophonic The minimum listening distance: 2 mAll listening positions should be w
31、ithin an angle of 30 from theloudspeaker axis.ITU-R BS.1116Two-channel stereophonic Base width: B = 2 m to 3 m (Value of B up to 4 m is acceptable in suitablydesigned rooms.)Limits of listening distance: D = 2 m to 1.7 BReference listening distance = B(Reference base angle = 60)ITU-R BS.1116The rela
32、tionship between base width, B, and display size, P, is given in Table 3.TABLE 3System type Viewing distance and display sizeITU-RRecommendationsConventional systems Viewing distance: 6 HDisplay size: 22 inITU-R BT.1128Conventional systems undercritical conditionsViewing distance: 4 H for 625 line s
33、ystems and4 H or 5 H for 525 line systemsITU-R BT.1128Enhanced PAL and SECAMsystemsViewing distance: 4 H and 6 H for the enhanced picture,4 H and 6 H for the compatible pictureDisplay size (16:9): 28 in(4:3): 22 inITU-R BT.811HDTV Viewing distance: 3 HDisplay size: 55 in(If not available, 30 in)ITU-
34、R BT.710Digital television systems at ornear the quality of conventionalsystemsViewing distance: 4 H and 6 HDisplay size: 22 inITU-R BT.1129All systems Maximum observation horizontal angle relative to the normal = 30 ITU-R BT.500Aspect/screenpositionCase A Case B16:9 P = 2.04 HB = D = 2 n H tan 30 =
35、 0.566 n P = 0.0144 n PP = 2.04 HB = D = n H = 0.490 n P = 0.0124 n P4:3 P = 1.67 HB = D = 2 n H tan 30 = 0.693 n P = 0.0176 n PP = 1.67 HB = D = n H = 0.600 n P = 0.0152 n PPicture height: H (m)Display size: P (m), P (in)Viewing distance: n HLoudspeaker base width: B (m)Listening distance: D (= B at the reference listening position).
