On the application of Vu meter and ppm meter in th

Talking about the application of Vu meter and ppm meter in the live broadcast room

volume meter is a special instrument for radio program monitoring. Its technical performance and quality will directly affect the broadcast quality. At present, the most widely used volume meters are Vu meter and ppm meter

characteristics of Vu table

at present, the most widely used volume meter in the live broadcast room is the "volume unit table", also known as Vu table (the abbreviation of volume unit in English). It uses the average detector (two-stage and bridge rectifier) and is determined according to the effective value of simple harmonic signal, so it is a quasi average table. Its scale is expressed in logarithm and percentage, and the reference level (0vu, 100%) is set at 3dB below the full scale, as shown in Figure 1

0vu (100%) of the standard Vu table is equivalent to the quasi average value of the signal of 1.228v. However, the required attenuator or amplifier can also be inserted during specific use. Therefore, the reference value of 0vu (100%) can be determined arbitrarily

the time characteristic of Vu meter

the indication action characteristic (i.e. time characteristic) of Vu meter is as follows: when the 1kHz simple harmonic signal reaches 0vu (100%) in the steady state. 2. From the perspective of service performance of Jinan experimental machine: when the vu meter is suddenly added, the time required for the pointer to reach 99% of the scale should be 300 ± 30ms, the overshoot of the pointer should not exceed 1.5% of the steady state value, and the overshoot swing should not exceed once; When the signal suddenly disappears, the time required for the pointer to drop from 100% to 1% should also be 300 ± 30ms. Figure 2 shows its indication action characteristics

vu meter reads the indicated value of sound signal as "volume unit value", also known as "Vu value". Although the VU meter also uses logarithm to express the quasi average value (level) of the signal, the indicated value (VU value) of the meter sometimes cannot keep up with the change of the actual quasi average value level (DB value) of the signal due to such a long integration time as 300ms, so the VU value cannot be confused with the DB value. At the same time, it can not fully reflect the audible loudness of the sound signal (because the latter requires shorter integration time), nor can it reflect the amplitude swing peak to peak of the sound signal (because the peak to average ratio of the sound signal varies with its waveform), which is the disadvantage of Vu table

ppm table

aiming at the shortcomings of Vu table, another kind of volume meter is gradually promoted, which is called "peak program meter", also known as ppm table (the abbreviation of peak program meter in English). Ppm table is actually a quasi peak level meter, because it uses peak detector to determine the scale according to the effective value of simple harmonic signal (also marked by level value). The biggest feature of PPM meter is that the pointer rises quickly and recovers slowly, which truly reflects the quasi peak change of sound signal, so as to avoid equipment overload and facilitate the effective control and utilization of the maximum dynamics of transmission and input system. Another feature is the wide range. The PPM meter has a 50dB effective scale, and there is usually a 5dB margin from its rated level (0dB) to full scale, as shown in Figure 3

0dB of the standard ppm meter is equivalent to the signal peak value of 1.55V, but the voltage value corresponding to 0dB in actual use can be determined according to the specific situation. In order to facilitate the measurement conversion between ppm meter and Vu meter in use, especially to facilitate the calibration of rated working level of electroacoustic equipment, PPM meter also indicates this level value on the scale. Generally, the PPM meter marks the corresponding level near its -9db (usually the interval of -6db~-12db). This is because from the range of quasi peak to average ratio (the ratio of quasi peak to quasi average value) of sound signal, the quasi peak to average ratio of general sound signal can be up to 2.8 times at most (9D do not abnormal, continue to use and cause major damage b). To take care of these high peak signals, the rated quasi average level of the visible signal should be 9dB lower than the rated quasi peak level (i.e. P3, 0dB on the PM table of the tensile performance test of butt fasteners). Therefore, if a simple harmonic signal with a quasi peak to average ratio of 1 (0dB) is used to calibrate the rated level, its indicated value on the SGS detection table of the international authority in foreign countries is 0vu, and those high peak signals on the PPM table will also be close to 0dB

comparison between Vu meter and ppm meter

when comparing these two kinds of volume meters, we should also consider the difference of their time characteristics. The time characteristics of PPM meter are specified as follows: its indicating value rise time is very short, generally 1~10ms; However, its decline time is quite long, generally about 1.5s, as shown in Figure 4

it can be seen that the PPM table can accurately reflect the sudden changes of strong signal envelope (rising fast), and it is convenient for the eyes to observe (falling slowly). In contrast, the VU table is much later. The indicated value (VU value) of Vu meter can't keep up with the actual quasi average level (DB value) of the signal, and the indicated difference between the two meters will exceed the quasi peak to average ratio of the signal, especially those sudden strong signals, which should be paid attention to in use

the size of the signal peak indicated by the PPM table, so it is used to monitor the actual situation of the signal amplitude swing; However, the peak size of the signal can not directly reflect the auditory intensity of the signal, so the indicated value of the PPM table can not represent the loudness of the signal, which is its disadvantage