Article reproduced with kind permission from LINE UP Issue 96, June/July 2004
Bow Tie Television
Digital OB Truck
DAVID SMITH MIBS describes the thinking behind installing the very first Calrec Sigma 100 digital console in an independent OB truck.
Bow Tie Television is an outside broadcast company based in Kent, with a variety of production vehicles and flyaway facilities ranging from two to 20 cameras, with both standard and high definition digital facilities. The company was established in 1990 to supply engineering and operational staff for the live television coverage of the House of Commons chamber. However, by 1993 it was clear that diversification was necessary if the company was to grow, and this led to them acquiring their first OB truck. When the contract with Westminster came up for renewal in 1996 the company decided to concentrate all of its efforts on the OB business, and set about building its first digital OB unit.
Three years ago the House of Commons contract came up for renewal once more. Bow Tie submitted a bid and won - the arrangement provides a consistent source of revenue as well as a useful staff training ground - but outside broadcasts remain the main element of the business accounting for about 75% of the annual turnover.
The company currently has five full OB trucks, plus a dedicated VT vehicle - all with digital vision systems. The smallest is a Mercedes panel van with four cameras and four video tape machines. Then there are two coach-bodied six-camera vehicles with four VTs; a 12 camera, eight VT vehicle; and the latest high definition capable truck built in an articulated trailer, with 20 cameras and 12 VTs.
Having been involved myself in the process of assessing and auditioning various digital desks for a news studio environment I was interested to learn how Bow Tie Television had arrived at their decision to purchase the Calrec Sigma 100 for this latest HD truck. To find out, I paid them a visit at their headquarters in Crayford, Kent where their new digital truck was being prepared in readiness for an OB.
Introductions
After a welcoming cup of coffee I found myself standing in the sound control area at the back of Bow Tie' digital OB truck talking to Chief Engineer Dafydd Rees. I asked him what factors were uppermost in his mind when it came to designing the truck and, in particular, why they chose Calrec's then brand new Sigma 100 digital desk. He explained that the company was looking to build a new truck that would serve for at least ten years. "It would have been easy to install tried and trusted technology, and while that would have left us with a truck that was ' comfortable' to work with from its first day out, it would also have been one which would have been immediately out of touch with the requirements of today' modern programmes and demanding production companies.
"We didn't want to be known as the company that built the last analogue truck! So we decided to stick our necks out. At a time when most market leaders were still installing analogue consoles, Bow Tie decided to go fully digital. We felt it was a risk, but a risk worth taking and the right thing to do. So, having looked at all the options from other manufacturers, we approached Calrec and bought the very first Sigma 100 digital desk to come off their production line.
"We have a large number of freelance sound engineers working on this truck and it was important that they would feel comfortable with the new sound desk. Most have worked throughout their careers with Calrec's analogue desks and even though the Sigma's operation is inherently different to that of an analogue desk, Calrec's ergonomics and approach are still broadly familiar. Also, because the truck was going to be involved in every conceivable type of OB operation from football to opera we felt the benefits of having a desk that could quickly be configured to previously stored settings would be a real benefit. It feels like an analogue desk and was designed to offer similar specifications and functionality to Calrec's S2 console (of which around one hundred are in use world-wide)."
Reliability
One of the biggest fears voiced by sound engineers about digital desks is that of reliability. On an analogue desk most technical problems can be worked around fairly easily because each channel and group is completely independent of its neighbours - a fault in one channel won' usually affect anything else. Digital desks, however, rely heavily on shared central processing to carry out all the ' crunching.' A system failure in that area could be catastrophic if the desk designers get it wrong.
Calrec has a long tradition of building high specification broadcast production consoles, and the company' experience shows in its line of digital consoles. The Sigma 100 may have been a brand new desk, but every element of it had already been tried and tested as part of the flagship Alpha 100 console - essentially the Sigma is a cut-down Alpha, with the same hardware and software and the same emphasis on reliability.
The Calrec approach is that for a desk to be 'reliable' in the broadcast sense it must meet the following criteria: it should never fail to pass audio; the controls on the desk should never 'freeze' after a loss of power the console must recover quickly and noiselessly to its previous state; and there should be no long-term deterioration in any audio or control performance factors. This may seem a tall order, but Calrec claims to have achieved it and feel that the lifetime reliability of their digital desks will be considerably better than the analogue equivalents.
Power Supply System
One of the main reasons Bow Tie chose the Sigma was that it offered a quick recovery after a power supply failure, and was able to maintain the previous audio paths even while the control surface re-booted. "With so many live events covered each year by the truck, we felt this was a high priority," explained Dafydd.
It is interesting to note that the console uses 'universal' power supplies that accept mains input voltages from 85 to 260V AC. These then deliver 24V DC supplies to power the console control surface as well as the I/O and digital processing racks. Each card and module within the desk carries local regulators to provide the necessary supply voltages: 5V for the panel logic and displays, 12V for the fader motors, 3.3V for the DSP chips, and so on. These local regulators can still function correctly even if the incoming power rails sag to 18V, providing a further 6V safety margin. Another interesting point is that the Sigma console has lower current demands than typical analogue consoles which means that power cabling and connectors can be smaller and lighter - space and weight are important issues in an OB truck. Furthermore, the low power consumption means that the cards and modules run fairly cool, and that translates to better long-term reliability.
To feel totally 'power-safe' during live events, the console is fitted with three separate power supplies. Calrec always supplies a 'hot' standby power unit which offers 100% back-up at all times. However, because these PSUs have cooling fans Dafydd decided to install them in the vision area of the truck, to maintain as quiet a working area as possible in the sound section. Sorry vision!
Control Processors and Redundancy
There are two main control processors in the system; one in the console and one at the processing rack. The console processor gathers the control data, generates the corresponding audio processing parameters, and transmits them to the DSP rack. The rack' own control processor then allocates this information to the appropriate DSP card. Each DSP card has a full set of 'state memories' to maintain not only the current settings, but also up to 99 other desk settings. Each processor has an associated back-up processor that can be switched in automatically if any one of a number of processor activities monitored by a 'watchdog' stops running. (Apparently, this is not possible on any system which uses a PC based control operating system). The console is as simple to power up as an analogue desk - taking less than 20 seconds - and comes up in the same state that it was in when powered down. This is obviously important for an OB truck where power is usually lost overnight and between locations.
No matter how reliable digital electronics are, there is always a possibility of component failure which, if it were a DSP card, could result in the loss of all of the main outputs or the entire monitoring, for example. To overcome these shall we say ' moments' the console rack includes a spare DSP card alongside the active cards. In the event of any DSP task stopping, for whatever reason, then those tasks will be loaded and run on the standby card. As all the tasks are held in flash EPROM on each card, the changeover is very quick and silent - only the audio paths through the particular card are briefly muted while the changeover occurs, and the faulty card is then electrically isolated from the back plane to prevent any spurious noise or data affecting the system. The console's diagnostics also alert the sound engineer that a fault has occurred and a changeover to the spare card has taken place, as well as indicating which card is faulty. Even if the console was being used in the middle of a live event the faulty card could be removed and a replacement installed with the power still on, and without any clicks or bangs on any audio path. The new card then takes on the role of 'hot spare'
Software
Calrec claims that the key to reliable software is modularity, where data is encapsulated within a module along with the functions that are allowed to change it. In this way data cannot be affected by more than one module, and unrelated effects cannot occur. It's also easier to change or add features to the system without introducing bugs in unrelated elements of the desk. I am unaware of any reports of software crashes on any of the Calrec digital consoles, so this approach must work well!
All of Calrec's digital desks employ a PC, but this is not essential for the continued operation of the desk during a show, and it can even be turned off if required. The PC is controlled through a touch screen monitor at the side of the desk, and is used mainly to store and recall console configuration settings, allocate network resources, and run the various diagnostic routines.
Saving Space
Space in OB trucks is always at a premium, but the compact Sigma 100 frame allows 48 faders across the width of the truck. In an analogue desk these 48 faders would be all that would be available to the sound supervisor, and accommodating other sound sources would require re-patching the appropriate channel(s). However, the beauty of a digital desk is that it can offer further 'invisible' fader layers - the Sigma has two. The Sigma console fitted in the Bow Tie truck provides 192 assignable inputs in all, of which 52 can be made available on the control surface at any time in a combination of mono and stereo sources. The I/O configuration caters for 48 stereo AES digital inputs, 80 analogue mic/line inputs, and 16 analogue line inputs.
I was surprised on first entering the sound area of the Bow Tie truck that there wasn't a window to look through into the production area. Dafydd explained that they had to drop that idea in favour of installing a full 5.1 surround monitoring system. On some occasions it has also been necessary to install temporary additional monitoring to cover 7.1 surround requirements, although the majority of work is still carried out in plain old stereo. Most of the time the truck is used for sport including ITV / SKY Premiership football, but it has also been used to cover large rock concerts and opera as well.
The three front monitors are Genelec 1030As - two way active near field loudspeakers - with a pair of smaller 1029As at the rear for 5.1 surround duties. The monitors employ stray magnetic field shielding, so the fact that they sit either side of colour TV preview screens is not a problem.
There are plenty of other toys to play with installed above and around the Calrec desk, including a couple of Sony MDS-B5 MiniDisc record/playback machines, a Yamaha SPX990 digital multi-FX unit, an HHB CD recorder, and a 360 Systems Short Cut editor. This can be triggered to playback stings from GPIs on the vision mixer. A 64 x 64 ProBel AES router is used to call up various digital audio sources throughout the truck, and a 64 port Telex Adam talkback system provides the communications.
The vast majority of audio pluggery entering or leaving the truck is by way of 26 pin multiways, located at the rear of the vehicle. Camera comms travel via the triax cables and the onboard CTP system offers independent talkback facilities for up to 20 cameras with audio circuits to and from production and engineering. Programme sound can also be fed down the same triax cable to each camera position if required. A CTP Sixmix-II line mixer is installed in the rack at the rear of the sound area to provide various mixed feeds for talkbacks and cue feeds, with six inputs mixing independently to six different outputs. The large central production area can seat 12 production staff, and has facilities for both high definition and standard definition video. The vision area at the front of the truck has both tape and hard disk facilities to record twenty-four separate vision sources.
Conclusion
I found my visit to Bow Tie Television, and in particular the chance to look at their latest digital OB truck, of great interest and value. It was reassuring to know that a company which has carried out technical operations in over 25 countries for hundreds of clients, has had the confidence to buy a relatively new product like the Calrec Sigma 100 digital desk. I don' think a company with some of the best independent outside broadcast facilities available would buy a console if they had any doubts over reliability. Indeed, recent history has proved they did the right thing as the Sigma 100 is living up to its claims.
Bow Tie TV
Tel: +44 (0)1322 524 500
www.bowtietv.com
Article reproduced with kind permission from LINE UP Issue 96, June/July 2004