1、STD-SMPTE 25LM-ENGL L77b 9 8357402 D002bL9 917 SMPTE STANDARD for Television Analog Recording - ANSVSMPTE 251 M-1996 Revision of ANSVSMPTE 251 M-I991 V2-h Type M-2 - Electrical Parameters of Video, Audio, Time and Control Code and Tracking Control - Page 1 of 18 pages 1 Scope ANSKMPTE 250M-1996, Tel
2、evision Analog Recording 1.1 This standard specifies the recording system for the video, audio, time and control code, and tracking-control signals for 1/2-in type M-2 helical-scan video tape recorders operating with video signals having a typical scanning structure of 525 lines, 59.94 fieldds, 2:l
3、inter- lace, and utilizing the video cassettes specified in ANSI/SMPTE 250M. - 1/2-in Type M-2 - Tapes and Cassettes ANSI/SMPTE252M-l996,TeIevisionAnalogRecording - 1/2-in Type M-2 - Pulse Code Modulation Audio IEC 268-12 (1987), Part 12: Application of Connec- tors for Broadcast and Similar Use 3 V
4、ideo signal recording 1.2 The audio frequency modulation (AFM) recording shown in this standard is optional. Pulse code modulation (PCM) audio recording mode with limited interchangeability, as defined in ANSVSMPTE 249M, is a secondary audio recording mode which is specified in ANSIEMPTE 252M. 1.3 W
5、here nominal values are given without tolerances, the interchange performance will be limited by implementation accuracy. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the e
6、ditions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent edition of the standards indicated below. Type M-2 video tape recorders shall record com- ponent video signa
7、ls and are intended to operate interchangeably in an NTSC environment. This component video recording system shall provide independent signal channels for the luminance and chrominance signals. These component signals shall be recorded on two independent tracks on the video tape as frequency modulat
8、ed signals. The two sepa- rate tracks shall be designated as the Y track for the luminance signals and the C track for the chrominance signals. The chrominance signals, in the form of R-Y and B-Y color-difference signals, shall be recorded in the form of a time compressed and time division multiplex
9、ed signal on the C track. (lhe AFM audio signal recording shall be recorded in the form of a frequency multiplexed signal together with the FM color-difference signal on the C track.) The PCM audio signal shall be recorded using the luminance and chrominance heads on the luminance and chromi- nance
10、tracks. 3.1 Luminance channel ANSI/SMPTE 12M-1995, Television, Audio and Film - Time and Control Code ANSVSMPTE 249M-1996, Television Analog Record- ing - 1/2-in Type M-2 - Records 3.1.1 Signal processing Asigna1 processing system, as specified in this stand- ard, shall contain the following element
11、s in the order of signal flow: CAUTION NOTICE: This Standard may be revised or withdrawn at any time. The procedures of the Standard Developer require that action be taken to reaffirm, revise. or withdraw this standard no later than five years from the date of publication. Purchasers of standards ma
12、y receive current information on all standards by calling or I writing the Standard Developer. Printed in USA. Copyright O 19% by THE SOCIETY OF L American National Slandard MOTION PICTURE AND TELEVISION ENGINEERS 595 W. Hamdale Ave., White Plains, NY 10607 (914) 761-1100 Approved November 29,1996 S
13、TD-SMPTE 25LM-ENGL L97b 83574DL 0002b20 b30 ANSVSMPTE 251 M-1996 1) Means for adding a timing burst signal to the luminance signal 2) Means for adding vertical interval subcarrier when appropriate 3) A luminance nonlinear preemphasis circuit 6) A linear frequency modulator having constant de- viatio
14、n with respect to the amplitude of the modulating frequencies 7) Acircuit for mixing the PCM audio CH5 signal to the frequency modulated luminance signal 4) A luminance preemphasis network 5) Means for clipping the preemphasized luminance signal to the amplitude of the modulating frequencies 8) The
15、recording current amplifier for the Y trackvideo heads y Beginning of field 1 i3 3. r ri 523 524 -525 1 2 3 4 5 6 7 8 9 10 11 12 Y Beginning of field 2 output load impedance = W. Figure 7 - Luminance preemphasis network input Y signal Input R-Y signal Compressed output load impedance = W. Figure 1 O
16、 - Chrominance preemphasis network Page 9 of 18 pages STD-SMPTE 251M-ENGL L77b 8357901 0002b28 721 ANCVCMPTE 251 M-1996 1 KOPTIMUM RECORD HEAD CURRENT O -1 dB AMPLITUDE 11 f2 Luminance channel Chrominance channel Blanking frequency Minimum chroma frequency 100% white frequency Maximum chroma frequen
17、cy Figure 11 - Record equalization 3.2.9 The frequency characteristics of the re- cording current shall be as shown in table 4. Table 4 - Recording current characteristics 1 Frequency (MHz) Relative level (dB1 0.4 Less than -30 0.7 Less than -30 2.0 O 3.3 Y-C timing 3.3.1 Reference of Y-C timing The
18、 timing difference between the Y signal, the R-Y, and the B-Y signal before time compression shall not be more than 5 ns as shown in figure 12. 3.3.2 Tolerance of compressed Y-C timing The timing difference between the luminance and the compressed chrominance signals shall be the value as shown in f
19、igure 2. 3.4 Vertical interval subcarrier (VISC) 3.4.1 VISC shall consist of one line of subcarrier inserted into each field of the Y signal as shown in figure 13. This signal shall only be present when the signal to be recorded is the result of decoding a composite NTSC signal with coher- ent subca
20、rrier. 3.4.2 The frequency of the VISC signal shall be equal to the frequency of the subcarrier of the NTSC video signal. 3.4.3 The phase of the VISC signal shall be within f 5“ of the burst phase of the NTSC signal prior to decoding. Page 10 of 18 pages STD-SMPTE 25LM-ENGL L77b 8357q03 0002b27 b8 A
21、NSVSMPTE 251 M-1996 I * 4000 * 20 6666 f 30 Ot5 Ot5 li- “Reference of Y C timing for Y signal 1.125 MHz 4 cycles of Y - C timing” for (R-Y) (End of the 2nd cycle) ignal 1.1 25 M Hz 4 cycles NOTES 1 Time base in nanoseconds. 2 Reference of Y-C timing shown displaced for illustrative purposes. “Refere
22、nce of Y C timing for (B-Y) signal (End of the 2nd cycle) Figure 12 - Reference of Y-C timing Page 11 of 18 pages STD-SMPTE 25LM-ENGL L77b m 8357403 0002b30 5T m ANSVCMPTE 251M-19W 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Fields 1 and 3 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 Fields
23、 2 and 4 C n nn nn nn nn nn nn nn n Detail of VISC signal Figure 13 - Waveforms of VISC signal 4 Longitudinal audio signal recording 4.1 Recording method Recordings shall be made by the anhysteretic (bias) method. 4.2 Recordingkeproducing reference levels 4.2.1 Recordingheproducing level indicator T
24、he audio recording and reproducing levels of this recorder shall be determined by using a standard volume indicator or its equivalent. 4.2.2 Recorder reference level For a 1-kHz sinusoidal signal recording which yields an rrns short circuit tape flux per unit track width on the record of 100 nWb/m k
25、 3 nWb/m, the recording volume indicator shall indicate its reference level scale mark. 4.2.3 Reproducer reference level For the reproduction of a 1-kHz tape record which yields an rms short circuit tape flux per unit track width of 1 O0 nWb/m, the reproducing volume indicator shall indicate its ref
26、erence level scale mark. Page 12 of 18 pages STD-SMPTE 251M-ENGL 177b 8357403 0002b32 4Lb 4.3 Frequency characteristics 4.3.1 Record flux versus frequency characteristics When a tape is recorded from a constant voltage applied to the input terminals, the short circuit tape flux level in the record v
27、ersus frequency characteristics, L$ (f), shall be expressed by the following equation: where L$ (f) is the relative tape flux level; f is the frequency at which the response is calculated; Fi is the low-frequency transition frequency, 50 Hz; and Fh is the high-frequency transition frequency, 4681 Hz
28、. 4.3.2 Reproduced flux versus frequency characteristics When a tape record having a short-circuit tape flux level versus frequency characteristics given by 4.3.1 is reproduced, the output voltage level of the repro- ducer versus frequency characteristics shall remain constan t. 4.3.3 Noisweduction
29、characteristics A noise-reduction process, if applied, shall have the static encoding characteristics shown in table 5. ANSVSMPTE 251 M-1996 4.4 Track usage (common audio mode) 4.4.1 Nonstereo audio The primary program audio channel shall be recorded on the audio 1 track. 4.4.2 Stereo audio When sep
30、arate channels are used for stereo audio, the left channel shall be recorded on the audio 1 track, and the right channel on the audio 2 track. 4.5 Program audio head phasing When the same signal is recorded on audio 1 and audio 2 tracks, the tracks shall be so phased that, when reproduced with a hea
31、d wide enough to sense the recorded flux on both records, the result will be additive. 4.6 Recording polarity When a positive-going waveform is present on pin-2 of the input connector, as defined in IEC 268-12, the audio head gap shall produce the magnetic flux which flows out of the north pole and
32、into the south pole. This flux flow shall be in the direction of the tape rnove- ment. Table 5 - Longitudinal audio frequency response of noise reduction encoding level Frequency (Ha 1 O0 200 300 500 Ik 3k 5k 1 Ok 15k UOTES Input level (dB) O -1 o -20 -30 -40 -50 -60 0.2 0.1 O O -0.3 -1.6 -2.3 -3.5
33、-6.3 0.9 1.5 1.6 1.7 1.5 -0.1 -0.6 -1.4 -3.3 2.7 5.3 6.1 6.3 5.9 3.7 2.9 2.6 1.5 2.9 8.0 10.7 11.8 11.4 9.2 8.4 8.2 7.3 2.9 8.1 12.0 15.6 16.2 13.9 13.5 13.6 12.2 2.9 8.1 12.0 16.2 19.4 19.2 18.7 18.1 15.0 2.9 8.1 12.0 16.2 19.6 20.7 20.4 19.2 15.0 I Input level is O dB, the reference input level at
34、 1 kHz. ? Encode level is O dB, the recorded reference level specified by 4.2.2. 3 Values are in decibels. Page 13 of 18 pages STD-SMPTE 253M-ENGL 377b 8357403 0002b32 352 ANSVSMPTE 251 M-1996 5 AFM signal recording (optional) Audio signals of two channels shall frequency modu- late two carriers. Th
35、ese frequency modulated carriers shall be located in the frequency region below the lower side band of the frequency modulated chromi- nance signal, which is specified by 3.2, in order to produce a frequency multiplex signal. The resultant multiplex signal shall be recorded on the chrominance track.
36、 5.3 Noise-reduction 5.3.1 Noise-reduction circuit Anoise-reduction circuit or its equivalent should be as shown in figure 14. 5.3.2 Compression ratio The compression ratio shall be 2:l in the logarithmic scale. 5.1 Signal processing 5.3.3 Transient response A signal processing system as specified b
37、y this stand- ard shall contain the following elements: 5.1.1 An audio noise-reduction scheme incorpo- rating compression 5.1.2 A linear frequency modulator having con- stant deviation with respect to the amplitude of the modulating frequencies 5.1.3 A means of adding the AFM signals to the chromina
38、nce signal in the ratios specified 5.2 Recording/reproducing reference levels 5.2.1 Recordingheproducing level indicator The audio recording and reproducing levels of this recorder shall be determined by using a standard volume indicator or its equivalent. 5.2.2 Recorder reference level When a 1-kHz
39、 sinusoidal signal recording is made with the reference deviation defined in 5.5.2, the recording volume indicator shall be adjusted to deflect to its reference level scale mark. The transient response shall be such that an attack time is 9.0 ms f 3 ms and a recovery time is 90 ms f 30 ms. Dynamic c
40、haracteristics shall be as shown in figure 15. 5.4 Preemphasis The output signal of the noise-reduction circuit speci- fied in 5.3 shall be preemphasized before the fre- quency modulation by a network as shown in figure 16. I 5.5 Frequency modulation 5.5.1 Carrier frequency The left channel (CH3) si
41、gnal frequency shall be 400 kHzf5 kHz. The right channel (CH4) signal frequency shall be 700 kHz f 5 kHz. 5.5.2 Frequency deviation The reference level deviation shall be 35 kHz f 0.7 kHz at 1 kHz. The maximum deviation shall not exceed C 105 kHz. 5.6 Recording head current 5.2.3 Reproducer referenc
42、e level When a l-kHz tape record with the reference devia- tion defined in 5.5.2 is reproduced, the reproducing volume indicator shall deflect to its reference level scale mark. The recording head current level shall be adjusted at 20 dB f 1 dB below the chrominance recording level defined in 3.2.8.
43、 The amplitude of the recording head current shall be constant over the frequency range from 300 kHz to 800 kHz. Page 14 of 18 pages STD-SMPTE 25LM-ENGL 199b 8357qil1 UilZb33 299 - T,=240ISw xw = 10 A0.2 x, - 1- x Level - Weighting network detector 41 1 VCA + NR emphasis ANCUSMPTE 251M-1996 Figure 1
44、4 - Noise-reduction circuit for AFM signals 0.25-1-0.2s-I t-o.2s-i- l I 5KHz Tine burst Attack time Recovery time Compressor output NOTES 1 O dB is input level corresponding to 2 HI= H2+2dB. Li= L2-2dB. reference levei. Figure 15 - Transient response of compressor for AFM noise reduction Page 15 of
45、18 pages ANSVCMPTE 251 M-1996 NOTE - Input source impedance = O; output load impedance = W. Figure 16 - Audio preemphasis network 6 Time and control code signal recording 6.1 Designated track for time and control code The longitudinal track identified as the time and con- trol code track shall be us
46、ed for recording the code specified in ANSVSMPTE 12M. 6.2 Recording method The recording shall be made by the anhysteretic (bias) method. Rb XD= -= 1.80 Rc be such that the S pole of the magnetic domain represents the direction of the tape travel. 7.3 Timing and period The polarity of the flux descr
47、ibed in 7.2 shall change to the opposite polarity when the recording of the next field is started by the channel 2 video heads. This opposite polarity interval shall continue until the be- ginning of the subsequent field recorded by the chan- nel 1 video heads as shown in figure 17. 6.3 Recording le
48、vel 7.4 Optional framing information The recording level, as expressed in peak-to-peak short circuit tape flux per unit track width, shall be 250 nWb/m f 50 nWb/m. 7 Tracking-control signal recording If implemented, the color framing information shall be carried out by changing the timing of the pol
49、arity transition of the control signal recording as shown in figure 18. 7.1 Waveform and level 7.5 Magnetization level The recording waveform and level shall be a series of constant flux levels alternating in polarity at a field rate and completing one cycle per frame on the longitudi- nal track identified as shown in figure 17. 7.2 Polarity of remanent magnetization During the time interval that video channel 1 is record- ing, the polarity of the tracking-control record flux shall The magnitude of the tracking control recorded flux shall be at least 30 dB above the residua
