Standard:ITU-R 468
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ITU-R 468 is a standard relating to Noise measurement currently maintained by the European Broadcasting Union who took it over from the CCIR.
It was previously CCIR Recommendation 468-4.
It defines a Weighting filter for use in weighted noise measurement, together with a Quasi-peak rectifier having special characteristics as defined by specified Tone-burst tests.
SUMMARY of SPECIFICATION (This is not the full definitive Standard)
Contents |
[edit] Weighting curve specification (Weighted measurement)
The weighting curve is specified by both a circuit diagram of a weighting network and a table of amplitude responses.
The ITU-R 468 Weighting Filter Circuit Diagram
Table of amplitude responses:
| Frequency (Hz) | Response (dB) |
|---|---|
| 31 | -29.9 |
| 63 | -23.9 |
| 100 | -19.8 |
| 200 | -13.8 |
| 400 | -7.8 |
| 800 | -1.9 |
| 1,000 | 0.0 |
| 2,000 | +5.6 |
| 3,150 | +9.0 |
| 4,000 | +10.5 |
| 5,000 | +11.7 |
| 6,300 | +12.2 |
| 7,100 | +12.0 |
| 8,000 | +11.4 |
| 9,000 | +10.1 |
| 10,000 | +8.1 |
| 12,500 | 0.0 |
| 14,000 | -5.3 |
| 16,000 | -11.7 |
| 20,000 | -22.2 |
| 31,500 | -42.7 |
The values of the amplitude response table slightly differ from those resulting from the circuit diagram, e.g. because of the finite resolution of the numerical values. In the standard it is said that the 33.06 nF capacitor may be adjusted or an active filter may be used.
[edit] Tone-burst response requirements
5 kHz single bursts:
| Burst Duration (ms) | Steady Signal Reading (dB) |
|---|---|
| 200 | -1.9 |
| 100 | -3.3 |
| 50 | -4.6 |
| 20 | -5.7 |
| 10 | -6.4 |
| 5 | -8.0 |
| 2 | -11.5 |
| 1 | -15.4 |
[edit] Repetitive tone-burst response
5 ms, 5kHz bursts at repetition rate:
| Number Of Bursts per Second (s-1) | Steady Signal Reading (dB) |
|---|---|
| 2 | -6.40 |
| 10 | -2.30 |
| 100 | -0.25 |
[edit] Unweighted measurement
Uses 22Hz HPF and 22kHz LPF 18dB/octave or greater (Tables to be added)
