1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T Supplement 22 TELECOMMUNICATION (Series P) STANDARDIZATION SECTOR OF ITU (03/93) TELEPHONE TRANSMISSION QUALITY SUBSCRIBERS LINES AND SETS TRANSMISSION CHARACTERISTICS OF WIDEBAND AUDIO TELEPHONES Supplement 22 to ITU-T Series P Recommendations (Previousl
2、y CCITT Recommendations) FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom-munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardiz
3、ing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. Supplement 22 to ITU-T Series P Recommen
4、dations was prepared by the ITU-T Study Group XII (1988-1993) and was approved by the WTSC (Helsinki, March 1-12, 1993). _ NOTES 1 As a consequence of a reform process within the International Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU Tele
5、communication Standardization Sector (ITU-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to references conta
6、ining the acronyms CCITT, CCIR or IFRB or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 In this Recommendation, the expression Administration is used for conciseness
7、 to indicate both a telecommunication administration and a recognized operating agency. ITU 1994 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing f
8、rom the ITU. Supplement 22 Series P (03/93) i CONTENTS Supplement 22 Series P (03/93) Page 1 Introduction 1 2 Handset sending characteristics . 1 2.1 Levels 1 2.2 Sensitivity/frequency characteristics 1 2.3 Noise. 2 2.4 Distortion 2 2.5 Discrimination against out-of-band input signals. 2 3 Handset r
9、eceiving characteristics . 3 3.1 Levels 3 3.2 Sensitivity/frequency characteristics 3 3.3 Noise. 4 3.4 Distortion 4 3.5 Spurious out-of-band receiving signals 4 4 Handset sidetone characteristics. 4 5 Handset echo path loss characteristics . 4 6 Hands-free sending characteristics. 4 6.1 Levels 4 6.2
10、 Sensitivity/frequency characteristics 5 6.3 Noise. 5 6.4 Distortion 6 6.5 Discrimination against out-of-band input signals. 6 7 Hands-free receiving characteristics 6 7.1 Levels 6 7.2 Sensitivity/frequency characteristics 6 7.3 Noise. 6 7.4 Distortion 6 7.5 Spurious out-of-band receiving signals 8
11、8 Hands-free echo path loss characteristics. 8 9 Hands-free switching characteristics 8 10 Delay 8 Annex A Objective measurement methods for wideband audio telephones 8 A.1 Introduction 8 A.2 Electrical interface specifications . 8 A.3 Electro-acoustic measurement considerations 9 A.4 Handset measur
12、ement methods. 9 A.5 Hands-free measurement methods 9 Supplement 22 Series P (03/93) 1 Supplement 22 Supplement 22 Series P (03/93) TRANSMISSION CHARACTERISTICS OF WIDEBAND AUDIO TELEPHONES (Helsinki, 1993) (referred to in Series P Recommendations) 1 Introduction This supplement provides preliminary
13、 audio performance requirements for telephones capable of transmitting an audio bandwidth extending beyond the conventional telephony bandwidth of 300 to 3400 Hz, to a bandwidth of approximately 150 to 7000 Hz. Such telephones are known as wideband audio telephones, and will make use of digital enco
14、ding schemes such as Recommendation G.722. Wideband audio represents a considerable departure from traditional telephony, offering significantly improved quality. However, since this is a new technical area, the requirements in this supplement are not complete, and studies are on-going. Guidance on
15、making wideband audio measurements may be found in the Annex A to this supplement. 2 Handset sending characteristics 2.1 Levels Pending completion of a method for calculating wideband loudness ratings, the electro-acoustic gain in the send direction should be adjusted in terms of a narrow-band loudn
16、ess rating calculated according to Recommendation P.79 (calculated over the range 200 to 4000 Hz). When measured in this manner the provisional send loudness rating (SLR) should be +8 dB (consistent with Recommendation P.31). NOTE The overload point for wideband audio is defined as +9 dBm0. 2.2 Sens
17、itivity/frequency characteristics The sending sensitivity/frequency characteristic from the mouth reference point (MRP) to the digital interface should fall within a mask which can be drawn between the points given in Table 1, also shown in Figure 1. All sensitivities are dB on an arbitrary scale. T
18、ABLE 1 Frequency (Hz) Upper limit (dB) Lower limit (dB) 100 4 125 4 7 200 4 4 1000 4 4 5000 4 6300 9 7 8000 9 2 Supplement 22 Series P (03/93) T1204670-92/d01105051015100 1000 10 000Response(dB)Frequency (Hz)FIGURE 1Handset send characteristicFIGURE 1.D01 = 8 cm 2.3 Noise With the microphone muted a
19、coustically, the noise produced by the apparatus in the sending direction at the digital interface should not exceed 68 dBm0 (A-weighted). 2.4 Distortion The distortion of the apparatus in the sending direction should be measured in terms of the total distortion (harmonic and quantizing) arising fro
20、m the application of 1 kHz and 6 kHz tones applied separately. The limits shall be as shown in Table 2. The tone input level is in terms of an acoustic reference level (ARL) which is defined as the acoustic level at MRP which results in a 10 dBm0 output at the digital interface. TABLE 2 2.5 Discrimi
21、nation against out-of-band input signals The level of any in-band image frequencies at the output resulting from application of input signals above 8 kHz should be attenuated by at least 25 dB compared to the output level of a 1 kHz input signal. Input level Signal-to-distortion ratio limit (dB) (dB
22、 re ARL) 1 kHz 6 kHz +18 to 20 35 29 30 26.5 25 46 12.5 11 NOTE These limits only apply up to the maximum sound pressure level which can be produced by the artificial mouth (+10 dBPa). Supplement 22 Series P (03/93) 3 3 Handset receiving characteristics 3.1 Levels Pending completion of a method for
23、calculating wideband loudness ratings, the electro-acoustic gain in the receive direction should be adjusted in terms of a narrow-band loudness rating calculated according to Recommendation P.79 (calculated over the range 200 to 4000 Hz). When measured this way, the provisional receive loudness rati
24、ng (RLR) is +10 dB. This is derived from the RLR of +2 dB specified in Recommendation P.31, with 6 dB loss added to account for the effective loudness gain going from narrow-band to wideband, and a further 2 dB loss to account for the loudness loss introduced by the Type 3.2 artificial ear specified
25、 in Recommendation P.57. It is anticipated that wideband audio telephones will incorporate a receive volume control, and the above requirement is taken to apply at the nominal volume level. NOTE The overload point for wideband audio is defined as +9 dBm0. 3.2 Sensitivity/frequency characteristics Th
26、e receiving sensitivity/frequency characteristics from the digital interface to the ear reference point should fall within a mask which can be drawn between the points given in Table 3, also shown in Figure 2. All sensitivities are dB on an arbitrary scale. TABLE 3 T1204190-92/d02105051015100 1000 1
27、0 000Response(dB)Frequency (Hz)FIGURE 2Handset receive characteristicFIGURE 2.D02 = 8 cm Frequency (Hz) Upper limit (dB) Lower limit (dB) 100 4 160 4 7 200 4 4 1000 4 4 5000 4 4 6300 4 7 8000 4 4 Supplement 22 Series P (03/93) 3.3 Noise The noise produced by the apparatus in the receiving direction
28、at the nominal receiving level specified in 3.1 should not exceed 35 dBA. 3.4 Distortion The distortion of the apparatus in the receiving direction should be measured in terms of the total distortion (harmonic and quantizing) arising from the application of 1 kHz and 6 kHz tones applied separately.
29、The limits shall be as shown in Table 4. TABLE 4 3.5 Spurious out-of-band receiving signals The level of any spurious out-of-band signals arising from application of in-band signals at a level of 0 dBm0 should be attenuated by the following amounts relative to the output level of a 1 kHz sine wave a
30、pplied at an input of 0 dBm0: 9 kHz 40 dB 14 kHz and above 60 dB 4 Handset sidetone characteristics Under study. 5 Handset echo path loss characteristics Under study, but provisional value of Weighted Terminal Coupling Loss is 40 dB. 6 Hands-free sending characteristics 6.1 Levels Following the appr
31、oach used for narrow-band hands-free telephones in Recommendation P.34, the levels in the hands-free send direction are related to those in handset mode with an allowance of 5 dB for higher talking levels and the difference in speaking position. The provisional value of SLR is therefore +13 dB, meas
32、ured in terms of a narrow-band loudness rating according to Recommendation P.79. NOTE The overload point for wideband audio is defined as +9 dBm0. Receive level Signal-to-distortion ratio limit (dB) (dBm0) 1 kHz 6 kHz +8 to 30 35 29 40 26.5 25 56 12.5 11 Supplement 22 Series P (03/93) 5 6.2 Sensitiv
33、ity/frequency characteristics The sending sensitivity/frequency characteristics from mouth reference point to the digital interface should fall within a mask which can be drawn between the points given in Table 5, also shown in Figure 3. TABLE 5 T1204200-92/d03105051015100 1000 10 000Response(dB)Fre
34、quency (Hz)FIGURE 3Hands-free send characteristicFIGURE 3.D03 = 8 cm 6.3 Noise With the microphone acoustically muted, the noise produced by the apparatus in the sending direction at the digital interface should not exceed 68 dBm0 (A-weighted). Frequency (Hz) Upper limit (dB) Lower limit (dB) 100 4
35、125 4 7 200 4 4 1000 4 4 5000 4 6300 9 7 8000 9 6 Supplement 22 Series P (03/93) 6.4 Distortion The distortion of the apparatus in the sending direction should be measured in terms of the total distortion (harmonic and quantizing) arising from the application of 1 kHz and 6 kHz tones applied separat
36、ely. The limits shall be as shown in Table 6. The tone input level is in terms of an acoustic reference level (ARL) which is defined as the acoustic level at MRP which results in a 10 dBm0 output at the digital interface. TABLE 6 6.5 Discrimination against out-of-band input signals The level of any
37、in-band image frequencies resulting from application of input signals above 8 kHz should be attenuated by at least 25 dB compared to the output level of a 1 kHz input signal. 7 Hands-free receiving characteristics 7.1 Levels Following the approach used for narrow-band hands-free telephones in Recomm
38、endation P.34, the levels in the hands-free receive direction are related to those in handset mode. The provisional value of RLR is +24 dB. It is anticipated that wideband audio telephones will incorporate a receive volume control, and the above requirement is taken to apply at the nominal volume le
39、vel. NOTE The overload point for wideband audio is defined as +9 dBm0. 7.2 Sensitivity/frequency characteristics The receiving sensitivity/frequency characteristics from the digital interface to the ear reference point should fall within a mask which can be drawn between the points given in Table 7,
40、 also shown in Figure 4. 7.3 Noise Requirements under study. 7.4 Distortion The distortion of the apparatus in the receiving direction should be measured in terms of the total distortion (harmonic and quantizing) arising from the application of 1 kHz and 6 kHz tones applied separately. The limits sh
41、all be as shown in Table 8. Input level Signal-to-distortion ratio limit (dB) (dB re ARL) 1 kHz 6 kHz +18 to 20 35 29 30 26.5 25 46 12.5 11 NOTE These limits only apply up to the maximum sound pressure level which can be produced by the artificial mouth (+10 dBPa). Supplement 22 Series P (03/93) 7 T
42、ABLE 7 T1204210-92/d04105051015100 1000 10 000Response(dB)Frequency (Hz)FIGURE 4Hands-free receive characteristicFIGURE 4.D04 = 8 cm TABLE 8 Frequency (Hz) Upper limit (dB) Lower limit (dB) 100 6 160 6 7 200 6 4 250 6 4 400 4 4 1000 4 4 5000 4 4 6300 4 7 8000 4 Receive level Signal-to-distortion rat
43、io limit (dB) (dBm0) 1 kHz 6 kHz +8 to 30 35 29 40 26.5 25 56 12.5 11 8 Supplement 22 Series P (03/93) 7.5 Spurious out-of-band receiving signals The level of any spurious out-of-band signals arising from application of in-band signals at a level of 0 dBm0 should be attenuated by the following amoun
44、ts relative to the output level of a 1 kHz sine wave applied at an input of 0 dBm0: 9 kHz 40 dB 14 kHz and above 60 dB 8 Hands-free echo path loss characteristics Requirements under study, but it should be noted that a wideband hands-free terminal may be required to provide inherent talker echo cont
45、rol. 9 Hands-free switching characteristics Requirements under study. 10 Delay Requirements under study. Annex A Objective measurement methods for wideband audio telephones A.1 Introduction This annex describes methods which may be used to measure the performance of wideband audio telephones, that i
46、s, telephones capable of transmitting an audio bandwidth extending beyond the telephony bandwidth of 300 to 3400 Hz, to a bandwidth of approximately 150 to 7000 Hz. Wideband audio is a new technical area, and measurement techniques are still evolving and studies on this topic are on-going. In genera
47、l, reference will be made in this annex to existing Recommendations where possible, noting any differences required to accommodate the wider bandwidth. A.2 Electrical interface specifications Wideband audio will be implemented by a digital encoding scheme such as Recommendation G.722, and will there
48、fore require a suitable interface for test purposes. Detailed requirements for such an interface are not yet available, but the same approach should be followed as for making measurements on narrow-band digital telephones in Recommen-dation P.66, see Figure A.1. T1204220-92/d05Codec derfrencelarge b
49、andePmPeWidebandaudiotelephoneDigitalinterfaceWi bandrefere ceCodecWidebandmeasuringequipmentFIGURE A.1FIGURE A.1.D05 = 5 cm Supplement 22 Series P (03/93) 9 A.3 Electro-acoustic measurement considerations A.3.1 Artificial mouths and ears The artificial mouth specified in Recommendation P.51 may be used for making wideband transmit measurements in handset and hands-free modes. If the Brel and Kjaer type 4
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