Peak programme meter
A VU (also: level meter ) is a device for controlling the modulation in sound recordings.
VU are required for proper modulation of an audio signal.
The display of the measured value is effected by mechanical pointer, laser pointer, light emitting diodes or liquid crystal displays. The physical properties of these ads affect the display characteristics of the Aussteuerungsmessers. LEDs and liquid crystals react inertia, mechanical pointer and light pointer on the other hand have a mechanical inertia and tend to design typical averaging. Therefore, the readings for various VU can not be compared directly with each other, depending on the signal obtained different levels dB indicators for the amplitude.
Most VU, for example in hi-fi equipment and software products that have an undocumented display behavior. The exact properties often known only to the manufacturer, when it was tested at all. In addition, there are standardized VU in a precisely defined display behavior that are used in recording studios, radio and television technology. These include the QPPM ( quasi-peak programs meters, quasi-peak level meter ), the SPPM (Sample Peak Program Meter), the True Peak meter (both peak level meter ), the VU meter and volume meter (ITU Rec BS.1770 and BS .1771 ).
- 3.1 Historical roots
- 3.2 VU- DIN
Technical Details
Ballistic properties
The ballistic characteristics of an analog Aussteuerungsmessers include:
- Inertia (integration time) differentiated according to settling
- Overshoot
- Return time
The display behavior of an analog Aussteuerungsmessers is not only determined by the physical design of its display instrument. The meter is preceded by a rectifier that is not working quite linear in practice. Likewise Drehspulmesswerke in practice not ideal linear.
VU meter with se inertia-free digital displays such as light emitting diodes, liquid crystal or fluorescent displays simulate in their measuring equipment such ballistic properties. This has proved in practice to be useful, because the eye is considerably slower than the ear. The picture looks much calmer and is therefore easier to read. Even the purely realized in software digital VU obtain an artificial inertia. The physical laws that apply to analog displays can be incorporated as a mathematical model in the software.
Peak level meter
Peak level meters measure the ( maximum ) amplitude values of electrical signals. This could be both positive and negative amplitudes. Prior to the measurement of a sound signal is this " rectified ", ie there are usually reversed the negative amplitude values.
An analog peak level meter (True Peak meter ) measures the peak value of an alternating electric voltage ( USS), so either the positive or the negative peak amplitude. Analog peak level meters for audio technology should have a sufficient accuracy, a response time (integration time) of ≤ 1 millisecond.
A digital peak level meter shows the simplest case, the largest ( individual ) sample value of an electrical signal to ( SPPM ). This true amplitudes are only statistically represented, because, higher values can hide between the samples, which are visible only after a sample rate conversion and D / A conversion. Would have to make the true amplitude values exactly visible the number of samples to be infinitely large according to an analog signal. In practice, an over-sampling ( oversampling) by a factor of 4-8 is sufficient to display the error to keep small and to be able to classify the instrument as a true peak meter.
Peak level meter to take in the transmission range before any frequency weighting.
Rectified value level meter
The standardized pointer instrument VU meter (DIN IEC 60268-17 ) is a Moving-coil movement. It displays the rectified value. The applied scaling is in the unit VU or decibels, the angle of rotation of the needle but is linear to the current displayed. Therefore, the scale is not equidistant. A VU meter averages the readings over the maximum design measurement period of 300 ms. It is therefore for dynamic signals and especially for short signal peaks at lower values than for continuous signals (sine ).
You lift with a rectified value - meter represents the reference point ( "0 dB " ) corresponding to the rectified value of a sinusoidal signal by 4 dB, as in the case of a conventional Messtons ( continuous sinusoidal signal ), the level value must not numerically from that of the peak voltage can be distinguished. This situation is referred to in literature as a common lead (lead ).
RMS level meter ( engl. 'root mean square ', RMS)
A rms level meter averaged rms voltage values over a maximum design measurement period. How can the English name ' RMS ' recognize instantaneous voltage values are to squared, with negative shares are reversed.
In a standards-compliant RMS level meter, the reference point ("0 dB " ) is according to the effective value of a stationary sinusoidal signal ( · USS; acc ≈ 0.707 · USS ) scales. To the sine signal the same indication must be raised by 3 dB to obtain as on a peak voltmeter measuring the effective value (RMS). Therefore, a conventional measurement tone yields equal dB ads on both instruments.
Music, speech or signals such as square or sawtooth, however, give readings that differ from the display of a peak level meter. For one, very short duration signals arise from the RMS rating significantly lower readings. A continuous square wave with an RMS meter for the reason previously mentioned by 3 dB "louder" appears as a peak level meter. This display property leads to the curious at first glance display of ' 3' dBFS for a full level square wave signal.
The RMS level meter takes in the transmission range no frequency weighting.
Volume diameter ( Loudness Meter )
Instruments for indicating volume work in principle as RMS level meter, but a frequency assessment is carried out, for example, the review by the A- curve in the transmission range.
Types
Indicating instruments in audio measurement technology are typical (dynamic ) Moving-coil instruments. The light pointer was used in analog Aussteuerungsmessern because of its low inertia, he also works with a Moving-coil movement.
Furthermore, there is plasma, fluorescent, LED, and LCD displays. Historically also the magic eye was used.
Analog environment
Historical roots
With the start of broadcasting technical development, the choice fell on a display instrument for electrical levels to the sufficiently fast and precise mirror galvanometer, in which also the characteristic dynamic behavior is justified. Their scale was initially only in " percent transmitter output control " calibrated; later, the now uncommon Napier and, on Bell United States, the calibration were added in decibels. The - unique as a German specialty - percentage scale occurred in the last decades more and more into the background, to have been replaced entirely by customary international dB with current devices. Exception is the consumer electronics, in particular, the VU meters.
VU- DIN
In a continuous analog signal paths are predominantly VU according to DIN 45406 ( German - VU ) are used. You have a calibrated in dB and percentage scale between -50 dB ( 0.3 %) and 5 dB ( 180 %). Their integration time (response time) is 10 ms, that is, a single pulse of 0 dB and 10 ms duration causes a display of -1 dB ( 90%), a peak of 0 dB and 3 ms duration a display of -4 dB. On the display even shorter peaks is waived, as such short overloads are no longer perceived ( in a similar environment ) by the human ear. The response time must be sufficiently large for easy reading; the standard provides a value of 1.5 s for a drop of 0 to -20 dB.
The 0 dB point of the scale ( 100%) is on an absolute level of 6 dBu (corresponding to 1.55 V rms for sinusoidal test tone ) calibrated ( ARD broadcasting standard level ).
The units have a button to increase the sensitivity by 20 dB, so that eg in modulation breaks external voltages can be read accurately. In addition, a calibration mark for the metrological verification of Tonfrequenzleitungen is mounted at -9 dB ( 35%).
Digital environment
The main contrast in audio engineering is not " Analog or Digital". As digital recording devices have emerged in direct competition to the analog method, and with them came up the digital mixing consoles and effects devices, this looks only at first glance like it.
The technical difference is rather by the - from a purely technical point of view - poor linearity analog recording method and tube technology. Their common characteristic is that they achieve the best compromise between ( high ) SNR and ( low ) distortion in the area of full scale. Above that ensure saturation effects of the analog tape technology and tube technology for the " pleasant sound ". Physically this is a non-linear signal variation similar to a compressor, mixed with pleasant sounding distortion caused by integer multiples of the fundamental ( = odd harmonics ). This effect is called the tape " tape saturation " and the guitar amp "overdrive".
In contrast, the digital audio signal processing, together with the analog transistor technology. Their common characteristic is that the clipping level of an audio input or channel has a fixed size. For digital signals, it is due to the system at 0 dBFS, based on individual samples. For analog transistor circuits it is slightly lower at the upper limit of the supply voltage, more specifically, for technical reasons, in practice less. In case of control of a digital device occurs virtually instantaneously, a significant increase in the non-linear distortion (clipping). However, this applies equally to the transistor circuit.
With the advent of digital technology also completely inertialess VU could be realized, which can accurately show the highest modulation on the bit. It has been shown in practice but very quickly that this inertia-free ads for modulation are unsuitable, the eye is much too slow. Also, the digital displays were taught an artificial inertia, at least they have a more or less strongly damped return time, so that the eye level peaks can still register.
VU meter for digital environments are standardized in DIN IEC 60268-18. The display, which is -60 to 0 dB, calibrated in dBFS; an indication of positive decibel values is not necessary because of the high response speed. These instruments are suitable for the detection of amplitude peaks, particularly in the audio production to avoid Klippung. However, it has been shown that a modulation of different audio genres can cause a serious imbalance between very sharp and containing dense ( compressed ) audio signals for ' true ' peak values as per DIN does not occur in the quasi-peak program meter. This imbalance affects in varying degrees of volume.
An additional phenomenon of digital VU is that these have been mostly only statistically true peak values in the form of samples show ( SPPM ), because, higher values can hide between the samples, which are visible only after a sample rate conversion and D / A conversion. This disadvantage try newer VU before the measurement by at least 4- fold oversampling ( oversampling) to avoid.
In the radio and television technology digital VU meters are used which simulate the ballistic properties of the standardized analog QPPM - Aussteuerungsmessers exactly. Thus, the operation could be taken from the analogue to the digital world. Here headroom ( headroom ) comes from 9 dB to fruition, as the peak values of speech or music can 3 to 6 dB above the display value of the standardized Aussteuerungsmessers. In rare cases occur even up to 9 dB. The derived from the EBU Recommendation R.68 9 dB headroom is especially true for VU with this ballistic behavior. This way of working ensures that neither analog nor digital audio transmission with distortion.
The display behavior of analog and digital Aussteuerungsmessern was determined by the radio Superintendents Conference in the document specification 3/6 1998. This document explicitly states that the specified there VU is not to be confused with the DIN -IEC 268-10 Type II and DIN IEC 268-17 standard equipment.
Implementation in other countries
Traditionally, in various European countries VU with different scales and the display characteristics in use. Their characteristics are described in IEC 60268-10. Accordingly, the following types can be distinguished:
VU- DIN IEC 60268-10 I meet the leaked in 2000 DIN 45406 with the difference that the integration time now with 5 ms to 80 % Display (-2 dB) is specified. Corresponding to the former DIN behavior (10 ms to 90 %). In Scandinavian broadcasters popular devices have the same properties, but a different scale ( " Nordic Scale" ) with a reference point at 0 dBu.
In the UK, VU meter with a scale division of " 1" to " 7" ( "British Scale" ) are common; are each 4 dB between tick marks. The reference point is at " 6", at a reference level of 8 dBu. These devices are standardized in DIN IEC 60268-10 IIa.
For international audio transmissions as part of the EBU devices according to DIN IEC 60268-10 IIb with a scale of -12 to 12 dB (bar corresponds to 2 dB) in use. The reference point is at 9 dB, the reference level at 9 dBu; a reference mark is placed at 0 dB (u).
Practice
The VU must allow for a precise and fatigue-free viewing. The technical implementation is in principle subordinate: " pointer tool " does not necessarily mean " VU meter "; " LED string " not necessarily " peak indicator ". The decisive factor is the nature of the upstream measuring amplifier ( rectifier ). So in German recording studios Drehspulmesswerke were quite common with pipe pointers - were widespread devices with light pointer - which were detached from the late 1970s of devices with LED chains or gas plasma displays. While previously measuring amplifier ( U70, U270, U370 ...) and display ( J45, J47, J645 ... ) were housed in separate enclosures, today exclusively integrated devices are on the market. These modifiers have a built-in correlation meter for displaying the mono compatibility.
VU are not suitable for a volume measurement and a volume comparison. Only with some experience can be concluded from the display approximately the volume balance. If different sound programs controlled at the same level, there are different loudness.
The different ballistic properties of Aussteuerungsmessern for analog and digital environment lead to difficulties in the practical assessment of the average level. Modulation with only a device having a short integration time tends to understeer as a seemingly higher average level is displayed by the display a very short peaks. Some VU meter can be switched to display their characteristic; for properly on but have to work with faster and slower at the same time display - that is, either with two devices or one device with combined display.
The built- in many devices from the U.S. or Japan VU meters have a fairly large integration time of 300 ms according to the standard display to signal peaks. These VU meters are therefore sometimes provided with an additional single LED to indicate the peak value, but this is an inadequate solution in practice.
For example, to comply with reasonable distortion limits is very difficult in hi-fi and home magnetic tape recorders. This can be a little offset by non-standard level meters. These indicators point to a conscious response distortion and ideally a combination of VU meters and peak indicators. In most Heimtongeräten but correct modulation in sound engineering point of view is hardly possible, neither in terms of the volume, nor with respect to the maintenance of a satisfactory sound quality ( achieving outstanding distortion limit).
In addition to the on ARD standard level ( 6 dBu ) calibrated Aussteuerungsmessern are increasingly on the international value for full scale ( 4 dBu, corresponding to 1.228 Vrms for sinusoidal test tone ) calibrated devices on the market. Therefore Modern VU have a switchable reference level.
As a manufacturer of Aussteuerungsmessern are essentially the company RTW ( Cologne) and DK -Technologies (formerly NTP, Denmark; brand name " DK- Audio" ) and Dorrough ( Woodland Hills, California, United States), represented (previously on the market for B and AEG -Telefunken, Siemens and EAB ). .
In addition to hardware devices, an increasing number of software- based VU meter that can be used for measurements in real time as well as for file -based workflows exist. They are available in the form of software plug- ins and / or as a standalone software. Some of the best known manufacturers of this are Dolby Laboratories ( San Francisco, USA), NuGen Audio ( Leeds, England), Penguin (Hamburg, Germany ) and TC Electronic A / S ( Risskov, Denmark). Most of these software-based VU meter can be set for different integration times and reference levels, many measure in addition to the electrical signal level is now also the loudness according to ITU BS.1770 -2, EBU R128, respectively.