1、,- CCIR VOLUME*X-1 90 Y855212 0504044 1 H Rec. 468-4 167 RECOMMENDATION 468-4 * MEASUREMENT OF AUDIO-FREQUENCY NOISE VOLTAGE LEVEL IN SOUND BROADCASTING (Question 50/10) (1970-1974-1978-1982-1986) The CCIR, CONSIDERING (a) sound-recording systems and on sound-programme circuits; (b) that it is desir
2、able to standardize the methods of measurement of audio-frequency noise in broadcasting, in that such measurements of noise should provide satisfactory agreement with subjective assessments, UNANIMOUSLY RECOMMENDS that the noise voltage level be measured in a quasi-peak and weighted manner, using th
3、e measurement system defined below: 1. Weighting network of the passive network shown in Fig. la. Table I gives the values of this response at various frequencies. equipment, comprising the amplifier and the network, are shown in the last column of Table I and in Fig. 2. The nominal response curve o
4、f the weighting network is given in Fig. lb which is the theoretical response The permissible differences between this nominal curve and the response curve of the measuring Z= 600 600 fi 12.88mH 33.06 nF 26.49rnH . D FIGURE la - Weighting network, simple form (A constant-resistance realization is de
5、scribed in Annex I) A tolerance of at most 1 % on the component values and a Q-factor of at least 200 at 10 000 Hz are sufficient to meet the tolerances piven in Table I. (The difference between the responses at 1000 Hz and 6300 Hz may be adjusted more precisely by a smaii adjustment of the 33.06 nF
6、 capacitor or by a different approach using an active filter CCIR, 1982-86al.) This Recommendation should be brought to the attention of the CMT. 168 CCIR VOLUME*X-l 90 4855232 05040Y5 3 M Rec. 468-4 12 8 4 O -4 -8 -12 s 2 -16 8 -20 2 -24 -28 -32 -38 -40 -44 -48 5 IO* 2 2 5 Frequency (Hz) FIGURE lb
7、- Frequency response of the weighting network shown in Fig. la Frequency (Hz) I 31.5 63 100 200 400 800 lo00 I 2000 3 i50 4000 5000 6 300 7 100 8000 9 O00 10 o00 12 500 14 000 16000 20 o00 31 500 TABLE I Response Proposed tolerance (dB) (dB) - 29.9 -23.9 - 19.8 - 13.8 - 7.8 - 1.9 O + 5.6 + 9.0 + 10.
8、5 + 11.7 + 12.2 + 12.0 +11.4 +10.1 + 8.1 O - 5.3 -11.7 -22.2 -42.1 f2.0 f 1.4(1) f 1.0 10.85() rr0.7 (I) rr0.55 (I) f0.5 rt 0.5 t0.5(1) f 0.5 (1) f 0.5 O +0.2(1) +0.4(1) 10/31 (LM Ericsson); 10/38 (OIRT); 101225 (German Democratic Republic). I CCIR VOLUMEMX-L 90 W 4855212 0504049 O W 172 CONSTANT RE
9、SISTANCE REALIZATION OF WEIGHTING NETWORK AUSTR. Rec. 468-4 ANNEX i IA FIGURE 3 - Constant resistance realization of weightirig network R (Q) CF) L (mH) Ro: 600 2Ci: 83.7 Li: 12.70 (for both windings in series) Ri: 912 C3: 38.4 by electrostatic shield) R2: 3340 Ri: 941 Cs: 23.8 Yi R: 300 cz: 35-28 L
10、2: 15-06 (for each of two windings separated 4: 7*99 LiA+B: 16.73 (two equal windings in series) c6: 13.94 L3c: c7: 35.4 L4 : LS : S: balanced L7 : A: unbalanced L6 : 4.18 (one winding, turns half L3A+B, can have large d.c. resistance, absorbed in R3) 20.1 (can have large d.c. resistance, absorbed i
11、n R3) 31.5 (with tap 20.1 at 0.798 of total turns) 13.29 8.00 BIBLIOGRAPHY 4 BROADCASTING C ISS10 Engineering Developmer tion of CCIR noise weighting network, Recommendation 468. . ANNEX II UNWEIGHTED MEASUREMENT Report No. 106 - Cons ant resistan I realiza- It is recognized that unweighted measurem
12、ents outside the scope of this Recommendation may be required for specific purposes. A standard response for unweighted measurements is included here for guidance. Frequency reqponse The frequency response shall be within the limits given in Fig. 4. This response .serves to standardize the measureme
13、nt and ensure consistent readings of noise distributed across the useful spectrum. When out-of-band signals, e.g. carrier leaks, are present at a sufficient amplitude, they may produce readings that are inconsistent between measuring equipments whose responses are different but still fall within the tolerance template of Fig. 4. CCIR VOLUME*X-L 90 4855232 0504050 7 Rec. 468-4 173 10 - 0- -6- -10 - -20 - 3 a -30- .Y -40 - -50 -60 - -70 - 1 2 5 22.4 HzJ I Frequency (Hz) 2 5 FIGURE 4 BIBLIOGRAPHY 103 2 5 105 16 kHz- L22.4 kHz Frequency (kHz) CCIR Dociments 1978-821: 10/76 (CMT114) (Canada).
