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1、 CEA Standard NTSC/ATSC Loudness Matching CEA-CEB11 May 2002 Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:48:27 MDTNo reproduction or networking permitted without license from IHS
2、-,-,- NOTICE CEA Standards, Bulletins and other technical publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtai
3、ning with minimum delay the proper product for his particular need. Existence of such Standards, Bulletins and other technical publications shall not in any respect preclude any member or nonmember of CEA from manufacturing or selling products not conforming to such Standards, Bulletins or other tec
4、hnical publications, nor shall the existence of such Standards, Bulletins and other technical publications preclude their voluntary use by those other than CEA members, whether the bulletin is to be used either domestically or internationally. Standards, Bulletins and other technical publications ar
5、e adopted by CEA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, CEA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard, Bulletin or other technical publication. This CEA Bu
6、lletin is considered to have International Standardization implication, but the International Electrotechnical Commission activity has not progressed to the point where a valid comparison between the CEA Bulletin and the IEC document can be made. This Bulletin does not purport to address all safety
7、problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Bulletin to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use. (From Project Number 5000, formulated un
8、der the cognizance of the CEA R4 Video Systems Committee.) Published by CONSUMER ELECTRONICS ASSOCIATION 2002 Technology Phone 202-828-3130; Fax 202-828-3131; Internet http:/www.atsc.org/stan Phone 800-854-7179; Fax 303-397-2740; Internet http:/; Email IEC Central Office, 3, rue de Varembe, PO Box
9、131, CH-1211 Geneva 20, Switzerland; Phone +41 22 919 02 11; Fax +41 22 919 03 00; Internet http:/www.iec.ch; Email pubinforiec.ch 3 Glossary ADC Analog to digital converter. compr A metadata control word contained in Dolby Digital (AC-3) bitstreams that introduces limiting when the decoder is in th
10、e RF operating mode. DAC Digital to analog converter. dBFS Acronym for decibels with respect to full scale. dialnorm A metadata control word contained in Dolby Digital (AC-3) bitstreams that adjusts or normalizes decoder gain to achieve normalized loudness or “dialog” level. Leq(A) A method of measu
11、ring audio loudness using an A weighted integrating-averaging sound level meter. PCM Abbreviation for pulse code modulation. PCM is sometimes used in the industry to describe digital audio signals or audio output format. RMS Root mean square. 1 Copyright Consumer Electronics Association Provided by
12、IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:48:27 MDTNo reproduction or networking permitted without license from IHS -,-,- CEA-CEB-11 4 Background Consumer broadcast products have evolved to a point where multiple services may be rec
13、eived by a single set top box (STB) or integrated receiver. Home users tend to set speech levels to a preferred constant acoustic level. Speech is an essential component of virtually all broadcasting. Therefore it is desirable for different media (NTSC, ATSC, DVD etc.) to deliver an approximately co
14、nstant speech level so that the listener does not need to significantly adjust the volume control for different sources. The gain structure proposed in EIA/CEA-CEB-11 was developed with the assumption that the Dolby Digital audio program was encoded with the correct dialnorm value that corresponds t
15、o the actual dialog level of the program material, and that the NTSC (analog terrestrial) and MPEG-1 Layer 2 (digital direct to home satellite) audio program levels were set in accordance with currently accepted broadcast practices for North America. 4.1 Leq(A) Leq(A) is a method of measuring sound
16、level that utilizes an integratingaveraging sound level meter that has an A frequency weighting characteristic. See IEC 60804, IEC 60651 and ISO 532. Leq(A) is one generally accepted method of measuring dialog in television program material. 4.2 Dolby Digital in ATSC Digital Television A Dolby Digit
17、al decoder has two operating modes. Line mode provides the highest quality (and offers the listener various options). However, its dynamic range is potentially much greater than that of NTSC and it is therefore not suitable to drive an RF modulator (at least, not with matching levels). RF mode is sp
18、ecifically designed to drive RF modulators, and offers a more limited dynamic range, similar to NTSC. Dolby Digital also carries a metadata control word, dialnorm, that varies the gain in the decoder and that is set at the encoder so that speech always emerges at a normalized level. In line mode, th
19、at level is 31 dBFS Leq(A) in one channel (e.g. center front of a 5.1-channel source) or equivalently for two-channel stereo, at 34 dBFS in both channels. In RF mode, it is 11 dB higher, 23 dBFS for both channels. Dolby Digital has greater headroom above speech peaks than NTSC, potentially 6 dB more
20、 in RF mode1 and 17 dB more in line mode. The latter allows the transmission of virtually any source (including wide- range movies) without the need for compression or limiting and with the speech normalized; depending on the equipment, the listener may have choices in the actual reproduced dynamic
21、range. In RF mode, the metadata word, compr, introduces limiting when necessary to prevent clipping. In either operating mode, it is possible for peaks to reach full-scale. 4.3 NTSC Current NTSC broadcasting is roughly normalized because most items, including speech, are controlled so that the signa
22、l peaks approach the highest permitted level. Measurement of a large number of channels indicates that the speech peaks are typically 2 dB below 100% modulation (after de-emphasis) and the equivalent loudness (A-weighted long-term RMS, abbreviated Leq(A)2) is typically 17 dB below 100% (either mono
23、or both channels together in stereo). On-air NTSC broadcasting has strict limits on maximum deviation, to avoid interference with adjacent channels. These limits are of no significance to RF modulators in STBs and VCRs. Measurements indicate that typical NTSC television tuners receiving the output o
24、f a mono modulator do not overload until the deviation is about 8 dB3 above the nominal FCC mono (baseband) limit of 25 kHz peak. 4.4 MPEG-1 Layer 2 In some equipment, NTSC and ATSC co-exist with MPEG audio. It is therefore desirable to match its level to the levels discussed in Section 4.3. However
25、, MPEG has no formal speech normalization requirements. Some channels control speech so that peaks approach full-scale, others keep the speech 1 With this extra headroom, Dolby Digital can provide a similar dynamic range to NTSC without the need for the violent non-linear processing commonly employe
26、d to avoid over-modulation. 2 Leq(A) more closely approximates loudness as perceived by human hearing when measuring of the subjective loudness of speech or dialog than either VU meters or PPMs. 3 The BTSC stereo and SAP system leads to a peak deviation of about 73 kHz, so it is not surprising that
27、in the absence of the pilot and subcarriers, a mono modulator/tuner can tolerate at least 8 dB above 25 kHz, 63 kHz. 2 Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:48:27 MDTNo repr
28、oduction or networking permitted without license from IHS -,-,- CEA-CEB-11 levels down to allow some headroom for louder sounds, and still others may leave several dB of headroom unused. The following assumes that signals can reach full-scale. MPEG has no operating mode specifically designed to driv
29、e an RF modulator, so all sources have to be controlled at the encoder input to allow passage through a modulator. If some, indeed any, MPEG channels can approach full-scale, clearly products must be designed so that full-scale does not cause overload. Thus for an RF modulator, 0 dBFS must not give
30、more than about 6 dB above the FCC limit. If MPEG channels set speech levels similarly to NTSC, with the peaks approaching full-scale, then clearly at the line outputs and at any pcm outputs, a match with NTSC and ATSC A/52A requires attenuation (0 dBFS in the MPEG signal = 17 dB below 2 V RMS and 1
31、7 dBFS in the output PCM). 5 Line Level Inputs Consumer digital equipment (CD, MD, DVD players etc.) have a standardized output level (per IEC 61938), 2 V RMS for full-scale. The same standard also requires that the input overload level for equipment shall be no less than 2.8 V RMS (3 dB above 2 V).
32、 This suggests that no source should ever be capable of delivering more than a dB or two above 2 V RMS. 6 Recommendation Summary Refer to Figure 1 and Figure 2. Table 1 provides a summary and supporting information. Putting all constraints together yields Table 1, which shows the necessary level/gai
33、n relationships to permit level matching between the various sources. Different equipment with these gains and levels can be interconnected to maintain the level matching. Source/ operating mode RF modulator relationship* (peak deviation) Level in ADC (if present) Baseband line (fixed) output level
34、(RMS). Variable outputs should not be greater. Dolby Digital RF mode 0 dBFS = 50 kHz N/A (digital output carries undecoded bitstream) 0 dBFS = 564 mV (11 dB below 2 V) Dolby Digital line mode 0 dBFS = 50 kHz N/A (digital output carries undecoded bitstream) 0 dBFS = 2 V RMS NTSC equal to source 100%
35、= 17 dBFS in ADC 100% = 283 mV (17 dB below 2 V) MPEG-1 Layer 2 0 dBFS = 50 kHz 0 dBFS in MPEG-1 = 17 dBFS in ADC 0 dBFS =283 mV (17 dB below 2 V) Line input N/A 2 V = 0 dBFS in ADC unity gain (overload 2.8 V) *In all cases, the RF modulation is obtained with the full-scale output from both channels
36、 simultaneously. Table 1 Recommendation Summary 3 Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:48:27 MDTNo reproduction or networking permitted without license from IHS -,-,- CEA-C
37、EB-11 This figure assumes that MPEG transmissions can reach digital full-scale. MPEG Audio Decoder Dolby Digital Decoder DAC Line/RF Mode Select RF Modulator Digital Select (Auto) Digital Output MPEG ATSC RF Select NTSCRF Output Digital Select Analog/ Digital Select RF Tuner Analog Line Outputs Vari
38、able Atten. Digital full-scale output: Dolby Digital line mode 2 V. Dolby Digital RF mode 564 mV. MPEG 283* mV. 100% FM: 283 mV. Variable attenuation (relative to 0 dBFS = 2 V rms): Dolby Digital RF mode 11 dB. Dolby Digital Line mode 0 dB. MPEG 17* dB. Default automatic switching: Dolby Digital bit
39、stream if present, otherwise PCM from MPEG. Digital full-scale: 50 kHz peak deviation 17* dB digital atten. (*provides match only for speech approaching full-scale) Figure 1 STB for North America 4 Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employe
40、es/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:48:27 MDTNo reproduction or networking permitted without license from IHS -,-,- CEA-CEB-11 5 Audio gain/level structure to allow level matching. This figure assumes that MPEG transmissions can reach digital full-scale. MPEG audio decoder
41、 Dolby Digital decoder DAC Choose dynamic range (line/RF mode) Digital select digital output MPEG ATSC NTSC Analog/ digital select RF tuner Variable atten. Digital full-scale output: Dolby Digital line mode 2 V. Dolby Digital RF mode 564 mV. MPEG 283* mV. 100% FM: 283 mV. Attenuation (relative to 0
42、dBFS = 2 V rms at line output): Dolby Digital Line mode 0 dB. Dolby Digital RF mode 11 dB. MPEG 17* dB. Default automatic switching: Dolby Digital bitstream if present, otherwise PCM. 283 mV equivalent to NTSC 100% (overload 2.8 V rms) 17* dB digital atten. (*provides match for MPEG speech with peak
43、s approaching full-scale) line input Power amplifier Volume control variable analog line output NTSC 100% = 17 dBFS. 2 V at line input = 0 dBFS. Digital select fixed analog line output Analog select ADC Overload protection Figure 2 Integrated Receiver for North America Copyright Consumer Electronics
44、 Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:48:27 MDTNo reproduction or networking permitted without license from IHS -,-,- CEA Document Improvement Proposal If in the review or use of this document, a potenti
45、al change is made evident for safety, health or technical reasons, please fill in the appropriate information below and email, mail or fax to: Consumer Electronics Association Technology & Standards Department 2500 Wilson Blvd. Arlington, VA 22201 FAX: 703 907-7693 standardsce.org Document No. Docum
46、ent Title: Submitters Name: Telephone No.: Submitters Company: FAX No.: e-mail: Address: Urgency of Change: Immediate: At next revision: Problem Area: a. Clause Number and/or Drawing: b. Recommended Changes: c. Reason/Rationale for Recommendation: Additional Remarks: Signature: Date: FOR CEA USE ONL
47、Y Responsible Committee: Chairman: Date comments forwarded to Committee Chairman: Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:48:27 MDTNo reproduction or networking permitted with
48、out license from IHS -,-,- Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:48:27 MDTNo reproduction or networking permitted without license from IHS -,-,- Copyright Consumer Electronics Association Provided by IHS under license with CEA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 03/30/2007 21:48:27 MDTNo reproduction or networking permitted