vu-Meter
A vu meter ( vu stands for english volume units, roughly " volume units ") is a VU meter, which is a measurement tool to assess modulation in audio engineering. Standardized according to DIN IEC 60268-17 shows it to the rectified value and is called Standard Volume Indicator ( SVI ).
Besides vu - meters, the device also VU meter or volume indicator (VI ) is called.
History
The vu -meter was originally developed by Bell Telephone Laboratories to facilitate the performance by adapting an easy- to-read gauge in the telephone transmission via cable. In 1961, in the ANSI C16.5 -1961 ( Bell Telephone Laboratories, Columbia Broadcasting System ( CBS), National Broadcasting Company ( NBC) worked out ) the specifications noted. It is vu " a quantitative expression of the signal amplitude in an electrical circuit " (DIN IEC 60268 Part 17 ).
Today's use
Today's level meters are usually built with LEDs or VFD and work as a bar graph with a peak identification. Here, the bar ( bar graph ) shows the current level, while a single LED stores the peak value and then slowly back again. In this way, two pieces of information are given: the current, music dependent fluctuating level and a few seconds occurred peak level. They are mainly used in professional audio technology, such as in recording studios. You can also run as software on the screen of the control computer.
While devices with vu meters up in the 2000s and in the private sector were widespread through the necessary in hi-fi cassette deck recording level, they are now rarely encountered in MP3 storage technology for storing music in the amateur field.
Construction
The vu -meter is historically a moving coil movement with an upstream wave rectifier and largely linear display. The main scale shows the log magnitude of -20 vu vu vu to 3. In addition, most also Percentages are stated. 0 vu corresponds to 100 %.
The vu - meter measures while the rectified value, usually with a slight tendency to the RMS value. A change from one vu corresponds to a change of one dB.
Characteristics
The settling time (integration time ) required for the vu - meters to vu to reach 99 % of the reference display 0 with a 1 kHz sine- duration signal of 0 vu must be 300 ms ± 10%. The overshoot of the pointer must be between 1 % and 1.5 % here. The return time after switching off the test signal is the same settling time. Through these ballistics a display characteristic is generated, which approximates the sensitivity of the human ear roughly.
According to standard between 35 Hz and 16 kHz, the deviation must be vu at constant voltage of the sinusoidal signal relative to the reference indication ( a sine wave signal of 1 kHz ) is less than 0.5.
Limitations
The vu -meter has a high inertia and does not respond to short-term peak values . This type of display could therefore not be established in Europe. From a technical point of view is considered to be insufficient, that short peaks will not be detected and displayed, and there is a risk that the signal is recorded with distortion. To still be warned against such controls, you give the instrument a so-called forward; English lead. These settings are based on experience or result from metrological conditions. In hi-fi equipment of the flow is often tied to the DOLBY level and different for each type of tape. Often 6 dB is called, but is really given either in the studio technology still in the consumer area. The engineer must be aware that a vu -meter with flow duration signals indicating with a correspondingly higher level. This is to be considered in calibration work. In " full scale " with the sine of the pointer swings to the top.
In Europe, devices have gained acceptance in the professional sound engineer, which react much more quickly to dynamic signals. It's VU meter, such as the peak -Programs- meter ( PPM / quasi-peak level meter ) and the SPPM, the time (integration time) and in terms of shape ( form factor ) show the ( quasi- ) peak. For digital sound, there are "real peak power meters ", see dBFS.