ITU-T P 78-1996 Subjective Testing Method for Determination of Loudness Ratings in Accordance with Recommendation P 76 - Telephone Transmission Quality Measurements Related to Spee.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU TELEPHONE TRANSMISSION QUALITY MEASUREMENTS RELATED TO SPEECH LOUDNESS P.78 02/96) SUBJECTIVE TESTING METHOD FOR DETERMINATION OF LOUDNESS RATINGS IN ACCORDANCE WITH RECOMMENDATION P.76 ITU-T Recommendation P

2、.78 (Previously “CCITT Recommendation”) STD-ITU-T RECMN P-78-ENGL 1796 I Li8b257L Ob25805 537 I FOREWORD The IT-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff

3、questions and issuing Recommen- dations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce

4、Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation P.78 was revised by the ITU-T Study Group 12 (1993-1996) and was approved under the WTSC Reso

5、lution No. 1 procedure on the 6th of February 1996. NOTE In this Recommendation, the expression “Administration” is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. O ITU 1996 All rights reserved. No part of this publication may be reproduce

6、d or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the IT. CONTENTS Introduction General . Experiment design Selection of crew members and speech material Calibration of the IRS . Circuit arrangements Recordin

7、g of information . 7.1 Details of the test 7.2 Individual balances . Analysis Presentation of results . Annex A . Examples of experiment designs Annex B . Selection of crew members, audiometric testing of subjects and speech material . B.l Crew members B.2 Audiometric testing of subjects - simple sc

8、reening procedure . B.3 Speech material . Annex C - Simplified statistical analysis . C.l Mean . C.2 Standard deviation Annex D - Direct loudness balance against the intermediate reference system (IRS) for the subjective determination of loudness ratings D . 1 Introduction . D.2 Method References .

9、Recommendation P.78 (02/96) . Page 1 1 3 5 5 5 7 7 7 7 7 11 13 13 13 14 14 14 15 15 15 15 17 1 STD-ITU-T RECMN P-7B-ENGL 177b 48b257L b25807 301 m PREFACE This Recommendation describes a subjective testing method which has been found suitable for laboratories purposes. Provided that the Intermediate

10、 Reference System (IRS) used complies with the requirements of Recommendation P.48 and that other requirements given in Recommendation P.76 are adhered to, the loudness ratings obtained by using the method given in this Recommendation can be used for veriQing the objectively measured loudness rating

11、s of telephone systems with special characteristics. This Recommendation, together with Recommendations P.76 and P.48, provides a definition of loudness ratings which can be used for planning. SUMMARY This Recommendation contains the essential particulars for defining the method for determining loud

12、ness ratings in accordance with Recommendation P.76 when use is made of subjects performing equal loudness balances. Details are included concerning the balancing method, choice of subjects, speech material, design of experiment, method of analysis and presentation of results. The method described i

13、n this Recommendation requires both the “unknown” telephone system whose loudness rating is to be determined and the IRS to be balanced against the Fundamental Reference System NOSFER. An alternative method, in which the “unknown” is directly balanced against the IRS, is described in Annex D. II Rec

14、ornmendation P.78 (02/96) Recommendation P.78 SUBJECTIVE TESTING METHOD FOR DETERMINATION OF LOUDNESS RATINGS IN ACCORDANCE WITH RECOMMENDATION P.76 (amended at Malaga-Torremolinos, 1984; Melbourne, 1988; Helsinki, 1993 and in 1996) 1 Introduction To compare the calculation of loudness ratings metho

15、d (see Recommendation P.79), a defined method of subjectively determining loudness ratings is required. This Recommendation deals with all aspects of a test from selection of operators to the method of analysis and finally presentation of results. 2 General In the subjective comparisons, the Fundame

16、ntal Reference System (FRS) is used (although other reference systems are permissible) as the datum for comparing the following speech paths: Path O - The fundamental reference system always provides the speech path against which each of the others is balanced. NOSFER set at 25 dB is used. Path I -

17、The send end of the test (“unknown”) local telephone circuit connected through the test (“unknown”) junction and an adjustable attenuator to the receive end of the test (“unknown”) local telephone circuit. The adjustable attenuator must be inserted in such a manner that the impedance relationships b

18、etween the three parts of the connection (send end, junction and receive end) are not disturbed. Path 2 - The send end of the intermediate reference system connected through an adjustable attenuator to the receive end of the intermediate reference system. Path 3 - The send end of the test (“unknown”

19、) local telephone circuit connected through an adjustable attenuator to the receive end of the IRS. Path 4 - The send end of the IRS connected through an adjustable attenuator to the receive end of the test (“unknown”) local telephone system. Path 5 - The send end of the IRS connected through the te

20、st (“unknown”) junction and an adjustable attenuator to the receive end of the IRS. The adjustable attenuator must be inserted in such a manner that the impedance relationships between the three parts of the connection (send end, junction and receive end) are not disturbed. In these subjective compa

21、risons, the junction of the fundamental reference system is fixed, i.e. the level of speech sounds received via the fundamental reference system is kept constant, the loudness balance being obtained by the so-called “margin” method, and the balance attenuator being that inserted in the telephone (or

22、 IRS) path being tested. The speaking position used with both the IRS and the test telephone sets should be as defined in Annex AlP.76. Figure 1 shows the composition of the telephone paths to be compared. The balances should be conducted using the vocal level defined in Recommendation P.72. Recomme

23、ndation P.78 (02/96) 1 STD-ITU-T RECMN P.78-ENGL L99b 48bZ54L Ob25809 184 Talker Listener (Sending end) (Receiving end) Path O - Fundamental reference system “Unknown“ LTS Adjusted for balance against Path O Path 1 - “Unknown“iUnknown/“Unknown“ I RS Adjusted for balance against Path O Path 2 - Inter

24、mediate Reference System (IRS) IRS Adjusted for balance against Path O Path 3 - “Unknown“/lRS “Unknown“ LTS IRS Adjusted for balance against Path O Path 4 - IRSfUnknown“ I RS I RS Adjusted for balance against Path O Path 5 - IRSIUnknown“/lRS NOTE - Direct loudness balance of the “unknown“ system aga

25、inst the ES is also possible (see Annex D). FIGURE UP.78 Arrangement of paths for subjective method of determination of loudness ratings The loudness ratings relative to the IRS as defined in Recommendation P.76 are: 2 Recommendation P.78 (02196) It is not necessary to include all the paths indicate

26、d above in every experiment. Paths O and 2 are essential but addition of only 3 and 4 is sufficient to determine sending and receiving loudness ratings of a local telephone circuit. Paths O, 2 and 5 are required to determine a junction loudness rating. Path 1 is usually required only when it is deri

27、ved to veri additivity of loudness ratings, namely that: OLR = SLR + JLR + RLR Note should be made that the loudness rating always involves the difference between the adjustable attenuator setting x2 for the IRS and the setting for the “unknown”. Since it can be expected that the value of x2 should

28、remain approximately constant from one balance to the next, at least one administration has found it desirable to perform direct balances of the “unknown” against the IRS with a fixed value of x2. Additional information on this direct balance method may be found in Annex D. 3 Experiment design To ha

29、ve confidence in results requires the correct testing procedures to be followed, coupled with the correct experiment design. The procedure should be prepared such that no ambiguity can exist. The following points must be considered in the design: a) The experiment should be designed in such a way th

30、at all uncontrolled influences operate at random, e.g. slight day-to-day drift of subjects and/or measuring equipment. b) If more balances are required than can be comfortably completed in one day, then the experiment must be designed such that equal numbers of each type of system are completed each

31、 day. c) The operators who start a test should always be the same throughout the test i. d) A minimum of 12 operator-pair combinations is suggested with a maximum of 20. Twelve operator-pair combinations can be arrived at from two crews of 3 (see Table 1 a) or one crew of 4 and 18 operator-pair comb

32、inations can be arrived at from one crew of 6 (see Table lb) and 20 operator-pair combinations from one crew of 5 (see Table 2a). NOTE - One crew of 6 giving 30 operator-pair combinations (see Table 2b) produces a larger test for only slightly more precision than the previously mentioned crew sizes.

33、 TABLE laP.78 Twelve operator-pair combinations from two crews of three, known as 3/6 operator method A B Operator C (talker) D E F I Operator (listener) ABCDEF X TABLE lbP.78 Eighteen operator-pair combinations from one crew of six, known as 316 operator method Operator (listener) ABCDEF I B Operat

34、or C (talker) D E F Recommendation P.78 (02/96) 3 STD*ITU-T RECMN P.78-ENGL Talker Listener Operator-pairs 3b sl Li8b259L Ob25833 832 A B C B C A e) When using two crews of 3, one can use both crews interleaved but it is generally more practical to separate the crews and use test crew 1 before crew

35、2. Members should not be used in both crews as it causes a bias and complicates the analysis. All operator-pair combinations should be tested in rotation, where practical, such that each operator takes a turn as talker, then listener and then has a break. f) a a Circuits TABLE 2dP.78 TABLE 2bP.78 3

36、1 2 2 3 4 1 4 3 4 2 1 Twenty operator-pair combinations from one crew of five, known as 515 operator method Operator (listener) 1 ABCDE A B Operator C (talker) D E xxxx X xxx xx xx xxx X Ix x x x Thirty operator-pair combinations from one crew of six, known as 616 operator method Operator (listener)

37、 (ABCDEF A B ODerator C (ialker) D E F xxxxx X xxxx xx xxx xxx xx xxxx X xxxxx g) The design of the experiment should eliminate any effect that could be attributed to the order of presentation. That is to say that all systems should be in a randomized order. To illustrate this point two examples are

38、 as follows: Example 1 If one type of loudness rating is required, with a given combination of telephone set and circuit condition, then the experiment design must allow for any effect associated with order of presentation for each operator-pair combination. An example is shown in Table 3. NOTE - Ho

39、wever, if a laboratory has found with sufficient evidence that this method of design is not necessary, then a simplified design may be used. TABLE 3P.78 Example to illustrate the elimination of order of presentation effect for one type of loudness rating CI CI (3 NOTE - When it is proven that there

40、is no difference for a given test crew and set of test conditions, the distinction between the order of path presentation can be eliminated. Path O presented before path traject 2 Path 2 presented before path traject O Path O presented before path traject 3 Path 3 presented before path traject O Exa

41、mple 2 Now, if more than one type of loudness rating is made or more than one telephone set is used, then there need only be one balance of path 2 against path O and vice-versa per operator-pair combination for any experiment, but this must be randomized within the experiment. An example is shown in

42、 Table 4. Recommendation P.78 (02196) STDmITU-T RECMN P-78-ENGL 197b E 48b257L Ob25812 777 m Operator-pairs Circuits Some experiment designs can be found in Annex A. Talker A B C Listener B C A a 3 1 2 a 5 4 6 l 1 2 5 1 6 5 3 2 2 6 4 2 4 3 1 TABLE 4P.78 4 Selection of crew members and speech materia

43、l Requirements for the selection of crew members including audiometric testing of subjects, as well as the speech material used by the crew for subjective tests, can be found in Annex B. 5 Calibration of the IRS It is most important that the calibration of the IRS is made before every test so that a

44、ny small change in SLR and UR can either be compensated for in the results or the sensitivity can be changed before the test. It is good experimental practice to check the sensitivity of the IRS after each experiment. The specification of the IRS is found in Recommendation P.48 and the description o

45、f the calibration procedure is found in Recommendation P.64. The results of the calibration are used to determine the corrections to the subjective balance results (see clause 9). 6 Circuit arrangements Figure 2 a) shows a typical circuit layout for the measurement of SLR and RLR. Figures 2 b) and 2

46、 c) show layouts for the measurement of JLR and OLR respectively. There is no reason if the experimenter so wished, why all four types of loudness rating cannot be tested in the same experiment. This, however, would require extremely intricate switching arrangements. In Figures 2 a), 2 b) and 2 c) t

47、he 600 ohm on the second position of switch S 1 allows the correct speech level to be set when path O is presented after path 1/2/3/4/5 (see Figure 1). This switch should be of the non-locking type and should be returned to the normal position as soon as the taiker has attained the correct speech le

48、vel. In order to reduce the effect of sidetone on the talkers vocal level during sending and overall determinations, the acoustic sidetone path of handset telephones should be disabled. This can be accomplished by placing the earphone in another identical handset and the electrical connections made

49、to the correct terminals on the telephone transmission circuit. The earphone can then be sealed to a P.57 artificial ear to give the correct acoustic loading. A simpler method, is to seal the earphone by means of heavy tape. Although this might not have the correct acoustic loading, in practice it has been found to have a negligible effect. If the microphone is of the carbon-granule type, then before each balance the conditioning procedure according to Recommendation P.75 should be used. Recommendation P.78 (02/96) 5 STD-ITU-T RECMN P-7