A VU (Volume Unit) meters used to be the mainstay of audio metering system. The Peak Program Meter (PPM) is notoriously bad at showing the peak signal level. This is a circuit that have function same of the explanation in above. In this circuit, the amplifier/rectifier is a simple LM1458 or similar dual op-amp, and buffers the rectifier circuit. This is the figure of VU meter;
The principle of the VU meter is a single diode is used in some, but the better ones will generally use a tiny selenium bridge rectifier or a germanium diode bridge. A capacitor is show, few budget VU meters will include it. As a result, the meter movement itself is uncontrolled in most of these meters, so overshoot is often huge, and the reading is almost useless. Because of the diode forward voltage, many of these meters also fail completely to register low level signals (< -20 dB). In figure 2, is shown of the meters ballistic control for the VU meter. The principle of this circuit is the values of R6, C1, C2 and C3 may need to be adjusted, depending upon the ballistics of the meter movement you use. Because meters vary so widely in this respect, it is only possible to provide representative values, although they should work quite well in practice. In order to get exact VU meter ballistics, it will be necessary to test the meter with a 300ms burst waveform at full scale (+3VU). It should reach 99% of full scale with up to 1% of overshoot before dropping back to zero. If we want to know about the result of the VU meter testing, we must make the circuit.
The principle of the VU meter is a single diode is used in some, but the better ones will generally use a tiny selenium bridge rectifier or a germanium diode bridge. A capacitor is show, few budget VU meters will include it. As a result, the meter movement itself is uncontrolled in most of these meters, so overshoot is often huge, and the reading is almost useless. Because of the diode forward voltage, many of these meters also fail completely to register low level signals (< -20 dB). In figure 2, is shown of the meters ballistic control for the VU meter. The principle of this circuit is the values of R6, C1, C2 and C3 may need to be adjusted, depending upon the ballistics of the meter movement you use. Because meters vary so widely in this respect, it is only possible to provide representative values, although they should work quite well in practice. In order to get exact VU meter ballistics, it will be necessary to test the meter with a 300ms burst waveform at full scale (+3VU). It should reach 99% of full scale with up to 1% of overshoot before dropping back to zero. If we want to know about the result of the VU meter testing, we must make the circuit.
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