Pro Security Installer

HomeSoftwareArchiveTop TipsGlossaryOther Stuff




Audio is becoming an increasingly important component in video surveillance, but relatively few multi-camera switching systems are equipped to handle a second signal path. The GBC AVS8 switcher is one of the exceptions, we’ve been looking at this compact, easy to use 8-channel audio video switcher



Before we go any further let’s get the bad news out of the way. Final assembly and quality control procedures at GBC appears to have some serious problems! Our sample AVS8 emitted a high pitched alarm signal the first time it was switched on. Despite re-initialising the unit several times the tone persisted. There was clearly a fault so we opened up the casing, to see if there was anything obvious, that could be put right.


The cause of the fault was immediately obvious. The wedge-shaped steel console is in two parts, on the bottom panel there’s a threaded stud set into the panel, for securing the mains earth wire. The stud is immediately adjacent to a small PCB, for alarm switching functions, the end of the stud was in contact with one of the tracks on the PCB, causing a short-circuit. Indeed the thread was so long that it had scratched the surface of the PCB. Fortunately this occurred on the low voltage DC side of the circuit, but the stud was only around 1 cm from the mains transformer. The consequences of such sloppy design are obvious!


Fortunately this was the only serious lapse in what is otherwise a generally well thought out product, though, as we shall see in a moment, the case design leaves a lot to be desired. The AVS8 is an 8 channel video and audio switcher, with several unusual features, apart from the audio switching facility. The first has to be simplicity of use. Instead of using on-screen displays or additional controls, all programming functions are carried out using just the 8 selector and two mode buttons, and their associated LED indicators. It has dual monitor outputs, each of which can be independently switched. Video switching employs a vertical interval delay, so that there’s negligible disturbance at the switching point when using phase line-locked cameras. It has an alarm input interface, associated with each camera input, that enables a number of programmed responses, and all settings are protected by a non-volatile memory.


The design is remarkably straightforward. On the top of the panel there are just ten buttons, each with a red LED indicator. On the far left is the monitor selector button. Next to that are the 8 camera selectors, and on the far right is the auto/manual sequence button. On the side of the console are two presets, one for setting the volume of the internal speaker, the second for adjusting the audio output level. On the back panel there are 10 BNC sockets, 8 for the camera inputs, and two for the monitor outputs. There’s a matching set of audio connections, and three multi-pin connectors. The 25-pin D connector is for the alarm inputs and outputs. The other two are marked ‘Auxiliary Connections’, and ‘Slave P1+3’ but no mention of them could be found in the instruction manual. They are connected to the main PCB, presumably they’re for future upgrades, but some indication of their purpose would have been helpful.


Normally we avoid delving too deeply into case design, except when there’s an obvious flaw, such as the earthing stud already discussed. However, the case on this product deserves further scrutiny as important adjustments can only be accessed from inside the box. In order to change the video connections -- factory set with 75 ohm termination’s -- it is necessary to open the case and remove resistors, soldered to the PCB. The manual broadly outlines the procedure, but do not give specific instructions, or identify the particular components. It does say that that; ‘it should only be carried out by staff qualified to, or experienced in, modifying mains-powered equipment’ but that’s not a sufficient warning, and would do little to deter a rookie installer, determined to ‘have a go’. Removing the case lid is easy enough, there are only two screws, but separating the two halves is quite tricky, and putting them back together again, without damaging the PCB, requires practice.


The external adjustments are a lot easier to carry out. The dwell time for the sequence can be altered from 2 to 60 seconds, in 15 steps. To do this the auto button has to be held down, with camera buttons 1 and 2 increasing or decreasing the dwell time. The approximate setting is shown by the blink rate of camera 1 and 2 LED indicators. This method is simple enough, and very economical in the use of controls, but it’s not very precise, and some trial and error may be needed to get the exact timing. It’s worth pointing out that this is a global adjustment, and it’s not possible to alter the dwell times of individual cameras.  


Camera inputs can be enabled or disabled using a similar technique. Holding down the auto button, (in the manual select mode), illuminates all 8 camera indicators; these can be individually included or excluded from the sequence by pressing the appropriate camera buttons.


There are various alarm options. Upon receipt of a trigger the switcher selects the relevant camera input, which can be routed to monitor output A or A and B. The display will remain on that camera for a pre-set period, from 4 to 120 seconds, the delay is set in a similar way to adjusting camera dwell time. After the alarm timer expires the sequence can be set to return to one of three states: back to auto sequence; remain on the alarmed camera, providing it was not in audio sequence prior to the alarm event; or return to the originally selected camera. The alarm interface is factory-set for normally open contacts, if it is necessary to have NC contacts then a link has to be soldered onto the back of the D-socket (supplied with the unit). Switched audio is routed through small built-in monitor loudspeaker, mounted on the right side of the case, and the audio outputs (one for each monitor) on the back panel.  


All programmed settings can be protected against accidental or deliberate tampering by a simple security feature. Holding down the ‘auto’ button at switch on displays the state of the programmed adjustments, which includes camera dwell and skip, action after alarm, alarm event display, auto sequence following an alarm and monitor access. These can be alternately enabled or disabled.



Video signals pass cleanly through the switcher, with no significant increase in noise, reduction in stability, bandwidth or colour fidelity. Camera switching is fast and on-screen disturbance at the switching points is minimal, even on non line-locked sources.


Needless to say audio quality from the 40mm on-board speaker is not that wonderful, though in most installations the output will normally be routed through to the video monitor.



The design of the case, and in particular the short-circuiting earthing stud is a cause for concern. We’re also unhappy about the method used to change video termination’s, some form of external switching would be preferable, and far more flexible, to removing resistors on a PCB panel.


Operationally, however, the AVS8 works well, the video and audio circuitry is largely transparent to the input signals, and the clever utilisation of the front panel controls contributes to ease of use.  



Video inputs                  8 x 1v p-p CCIR/PAL composite, terminated 75 ohms

Video outputs             2 x 1v p-p CCIR/PAL composite, terminated 75 ohms

Video bandwidth            more than 6Mz

Video crosstalk            less than -48dB

Sequence timing   2-60 seconds in 15 steps (2/3/4/5/6/8/10/12/15/20/25/30/40/50/60 seconds)


Alarm timer                   4-120 seconds in 15 steps (4/6/8/10/12/16/20/24/30/40/50/60/80/100/120 seconds)

Alarm inputs                  8 x N/O, via 25-pin D-Sub connector

Alarm output                  N/O for VCR triggering (rated 28V DC 0.5A max)


Audio inputs                  1v p-p 600 ohms

Audio bandwidth            100Hz to 10kHz


Power supply                 230 VAC 50Hz

Weight              0.7kg

Dimensions                   153 x 62 x 284mm





Product             7

Product design            5

Build quality                  5

Ruggedness                  7


Operation                      7

General functions            7

CCTV functions            8         

Ease of use                   8

Instructions                   6

Manuf. support            ?                     



Video quality                 9

Switching                      9

Audio                            8


Ó R. Maybury 1996 2511




[Home][Software][Archive][Top Tips][Glossary][Other Stuff]

Copyright (c) 2005 Rick Maybury Ltd.