Tektronix instruments for audio signal measurements

By Anatoly Belostotsky

Review contents:

Audio accompaniment for TV programs The audio measuring equipment from LES Company Headphones and sets from Beyerdynamic Systems from D.A.S. Audio Monitor systems from Digilab Electronics Sound monitors ESI Acoustic systems for audio control in TV production. Monitors from Event Electronics Active sound monitors of the Fostex Company Devices for the audio control from Genelec Company Sound monitors from JBL Pro Equipment of Klark Teknik Company Loudspeakers KRK Audio equipment M-Audio Audio equipment Mackie Marshall Electronics monitors Monitors and headphones from Samson Snell and Wilcox equipment for the embedded audio control Tektronix instruments for audio signal measurements Production of Wharfedale Pro Yamaha monitor loudspeakers

Tektronix trade mark is widely known to specialists all over the world, including Russia. Engineers, scientists not only from Moscow and St. Petersburg, but also from other cities of Russia use measuring devices of this company.

This equipment guaranteed the measuring accuracy, convenience in operation, reliability and ergonomics. Devices provide with high noise immunity, allow to carry out measurements in a wide frequency range.

Essential expansion of opportunities of reception of trustworthy information about measured equipment or researched path conditions is relied on application of microprocessor engineering, built-in RAM and disk drives, availability of software and interfaces with personal computer and network equipment.

The wide choice of devices for TV measurements which are produced by Tektronix, allows analyzing both TV and audio signal parameters with high accuracy and in complex.

First of all it would be desirable to mention about automated measuring complex VM700T which is well-known to the TV specialists engaged in repair and adjustment, development and researching of video and audio signals. This device is intended for every possible complex measurement in hand-held or automatic modes in analog and digital equipment rooms. Options VM700T 40 or VM700T 41 may be included in the complete set of delivery of the device for research of audio signals which are connected to input of the device through matched cable-adapter.

VM700T measuring device

The device is provided with extensive configuration menu by which, according to carried out measurement, it is possible to establish the range of input signals in V or dB; type of scale (linear, logarithmic); opportunity to choose necessary mode of operation, etc.

Measurement of an audio signal will be carried out in one of four modes: audio analyzer, audio monitor, spectrum analyzer, audio control over test signal.

In a mode of audio analyzer the frequency characteristics of two (left and right) audio channels are displayed on screen VM700T. Besides, the display can present the frequency of measuring signal, its level, value of harmonic distortions, noise level, and also values of mismatches over phase and over level between channels.

In the audio monitor mode on Lissajous screen the phase ratios of signals in two channels (either in coordinates X-Y or in orthogonal system of coordinates) are displayed. Besides on the screen three vertical indicators of level are simultaneously displayed: left, right channels and total. Scales may be chosen in any of three standards — DIN, Nordic or PPM (decibels or volts).

In mode of spectrum analyzer it is possible to analyze a spectrum of test signal in each channel and to carry out the measurements with the help of two cursors, for example, to measure peak-to-peaks of base signal and one of harmonics.

In the same mode also it is possible to determine the level of harmonics on some frequencies (for example, 50 Hz) in the range 20 Hz…20 kHz on each channel.

The device also may operate in the mode of automatic testing of the measuring audio signals which are corresponded to the Recommendation O 33 Tek/ANSI or CCITT. As a source of signals it is possible to apply one of Tektronix’s audio-signal generators — ASG100 or ASG140 which support these recommendations.

In mode of the multifrequency analyzer it is possible to carry out the audio measurements (frequency characteristic, interchannel differential gain and phase distortions, noise measurement etc.) over several frequencies simultaneously.

The option 41 allows to expand the number of device inputs to three. In this case all spectrum of measurements described earlier for each of the chosen channels is possible as well. For connection of studying signals to the device the 37-contact connector is used.

With the exception of automated device VM700T, Tektronix produce two meters (monitors) of audio signals: 760A — stereo monitor for the analog signal analysis and 764 — monitor for the digital signal analysis.

760A meter

With Tektronix 760A it is possible the measurements of analog stereo signals to carry out. For this purpose on the front panel of the stereo monitor are located the screen of high resolution for display of Lissajous figures on which it is possible to check the phase ratio of signals in two channels (either in coordinates X-Y or in orthogonal system of coordinates). And on the right from screen three vertical indicators of level measured signals (left, right channels and total) and controls are placed. The device is produced in three versions and each of them is indented for measurement of signals in standards PPM, DIN and Nordic accordingly.

At the range of input signals +8…45 dB the sensitivity of the device may be established on 0, +4, +8, +12 and +16 dB.

The device may be used in control services of program manufacturers, transmitting and receiving centers.

As against to simpler analog monitor, the Tektronix 764 is the monitor of digital signals and provided with many characteristics necessary for the analysis of digital audio signals.

Tektronix 764 digital signals monitor

Device Tektronix 764 is provided with two inputs for measurement of AES/EBU signals. In addition, with the help of option 01, it is possible to analyze the sound embedded into digital video stream. Further, the option 02 allows controlling the studied digital signal on the analog control monitor.

As well as in the device 760A, at 764 there is the Lissajous display for the control of phase ratio between audio signals in one of the chosen groups of digital sound. With graphic indicators of level it is possible to control the amplitudes of these signals, and by the correlometer it is possible to valuate the correlation between signals.

Besides the available input for external genlocking of the device allows to valuate time delays of the audio signals; then the time code signals coming to separate input (LTC or VITC) may be used as reference time signals at various statistical measurements. There is also an opportunity to control some other parameters, such as quantitative excess of dynamic range, number of sound losses, essentially vertical (VITC) or longitudinal (LTC) time-code, the channel status and the data of the user. Instead of Lissajous screen on the display may be presented so-called screen of the statistical data.

For convenient operation the device is provided with an additional output for connection of VGA monitor. The device allows to carry out the measurements of audio signals in the range -80…0 dBFS.

As generators of audio signals Tektronix offers two devices differed by number of channels — ASG100 and ASG140.

These are generators of sine wave signals intended for application at adjustment, repair and service of sound path. They may originate the signals of various frequencies in the range 20 Hz…20 kHz over frequency and -90…+24 dBu over level, and additionally — sweep-signal for valuation of frequency characteristic, as well for checking of transient distortions between channels. Besides, as it was specified above, these devices support the Recommendation CCITT  O.33 and may be used together with VM700T for so-called multisignal (multitone) measurements.

Control of devices is realized from the front panel. Besides, the remote control over interface RS-232 is possible.

In addition to the above listed specialized devices for the audio signals control Tektronix is provided the equipment intended for TV signal formation and analysis, with the built-in analyzers and/or generators of audio signals.

WFM700 measuring device

WVR600 rasterizer

So, for measurement of AES/EBU parameters of audio signals the analyzer of the form of digital TV signals WFM700 may be equipped with the additional module DG, allowing to control up to eight channels of digital audio. Functionally this module is similar to the device 764.

Portable, but powerful analyzer both analog and digital TV signals WFM91D, intended for operation in hybrid studios and allowing to analyze analog composite and digital component TV signal, is provided with built-in analyzer of analog accompanying sound signal.

The raster analyzer of analog and digital TV signals of WVR600 series has options AN, DG and DA for the control of analog and/or digital audio signal. In this case the opportunities of the audio signal controls are much wider, than at the monitors of audio signals 760A and 764 described earlier.

All TV generators /sync generators of Tektronix have an opportunity to generate test audio signals also.

Sync generator SPG422 may form not only digital test video signals, but also digital audio (AES/EBU and embedded) signals used during adjustment of the equipment.

The portable generator TSG95 intended for formation of analog PAL/NTSC signals, on its output provides a line of audio analog signals with frequency 50…20000 Hz. There are three fixed amplitudes of audio signal.

TG700 generators

In modular TV generator TG700 various units, including the unit of the digital audio generator AG7 may be established. It provides eight channels (four AES/EBU pairs) of digital audio. Besides two channels (one AES/EBU pair) of digital audio with zero level and the timing signal 48 kHz are provided. In module DVG7 (digital video) there is the built-in generator of the embedded audio (16 channels) with 20- or 24-digit encoding. The same generator is installed in module HDVG7 (digital video of high resolution).

The multistandard generator of TV signals TG2000, the module DVG1 (digital video) are provided with the built-in generator of embedded and AES/EBU audio.

Material provided by Annik-TV Company