Calrec's Alpha and Sigma

At the Augusta Golf Classic in April, I had the opportunity to realize an idea that I have been championing for more than six years — a large-scale delivery of quality audio signals over almost an entire TV compound using MADI. CBS Sports has televised this tournament for 54 years, and it ranks as one of the premier sporting events of the year. So, the opportunity and the challenge were both immense. I have been fortunate enough to have worked for CBS for 10 years at this event, and the differences in technology from my early days to last April are truly amazing. Broadcast has gone from analog to digital, SD to HD, stereo to 5.1, tape to X-file servers, and so on.

MADI is not new technology. It was first introduced to me in the mid-1990s, along with the first digital consoles. The SSL Aysis used MADI streams to connect its hub-router to the outside world.

What struck me as peculiar was that even after years, few people knew how the transportation of signals took place. MADI was that reliable; it never failed, so few knew it was even there.

Over time, MADI devices became more available. The big break came in about 2007, when router frame interface cards started to appear. At about the same time, Calrec was offering a two-channel rack unit for interface to its Alpha audio console. Now all I needed was someone who would take my ideas and integrate them in a mobile unit design.

My break came during the construction of the mobile units designated HD-12 from NMT. Thanks to the trust and support from so many people at CBS, NMT and VSG, I was able to contribute to the build process and audio design of the mobile units that CBS Sports now uses for its golf and NFL coverage.

CBS golf events

On a week-to-week basis, NEP SS-10 (formerly NMT HD-12) moves from remote to remote televising the PGA. Every week, six single coaxial cables, along with two backups, are all that are needed to connect the “B” unit main mix position to the “C” unit submix position and Adder II modular audio, intercom and data multiplexing system from Telecast Fiber Systems.

This meets all audio needs. That is up to 384 signals or 192 AES pairs. There are none of the old analog artifacts like hum, buzz or bad pairs. Each cable delivers up to 64 signals (32 AES pairs) as a send or receive, and they are all or nothing. This means that if the stream is working, it arrives intact. If it doesn't, then simply change the cable, and off you go.

The Augusta Golf Classic

This remote is huge, requiring 16 mobile units involved in different capacities. Many require massive amounts of audio signals to be delivered to them. Figure 1 on page 72 is a single-line schematic of the signal flow around the compound. Requirements for each mobile unit are unique. The main or back “9” truck requires almost every signal in the compound, while the truck labeled “ESU” distributes and receives signals to and from the international broadcasters.

There are mobile units set up as additional tape support, and these require their internal router to be populated with all course effect mics, as well as programs from various other trucks and other VTR sources. CBS employs a “QC” position where a mixer needs to be able to listen to all on-air sources in the compound and, if necessary, set the tone for level and EQ so that the different outputs from other units sound similar.

In addition, this year, CBS supplied coverage for the entire par three event held on Wednesday, in effect adding an additional nine holes — another half of a golf course — to the mix. There were two submix trucks, each doing about half the course. Each mixer was responsible for upwards of 75 sources, in addition to seven announce towers and a “Butler Cabin Studio set.”

Add to that the Internet and highlight shows, and you begin to see how large this event's setup was. If this was not complicated enough, signals came and went in analog and digital formats, as well as embeds, e-streams and now MADI.

MADI defined

The specification provides for the serial digital transmission over coaxial or fiber-optic lines of a sequence of 64 channels of digital signal contained in a frame numbered 0 to 63. Sampling rates range from 48kHz up to 96kHz (48kHz being the sampling frequency used by CBS) and resolution of up to 24 bits of audio per channel — delivered in this case on a 75Ω BNC connector and coaxial cable. The basic data rate is 100Mb/s of data using 4B5B (four bits/five bits) to produce a 125MHz physical baud rate.

As sample rate changes, non-return-to-zero inverted data rate stays constant; transmitter and receiver are asynchronous. Each channel consists of 32 bits, of which 24 are allocated to audio. A further four bits represent the validity (V), user (U), status (C) and parity (P) bits of the two-channel AES3 interface, with a further four bits allocated for mode identification.

The assets included four mobile units equipped with MADI interfaces, some with both the MADI I/F R/U interface and router interface card connections, and some with only the MADI I/F R/U interface. To round out the plan, I employed some SDI DAs and a 5RU Cobra Net system. The combinations were the tricky part — when to send to a router interface, when to send peer to peer to another console, which streams to duplicate for DA distribution and, of course, what should populate each MADI stream. The assets broken down by mobile unit are illustrated and annotated below:

  • NEP SS-10B: Eight MADI-to-router interfaces (eight send/eight receive); two Calrec MADI interfaces for each two-channel (two send/two receive) for a total of four send and four receive from the Calrec Alpha.
  • NEP SS-10C: Two Calrec MADI interfaces, each two-channel (two send/two receive), for a total of four send and four receive from Calrec Sigma.
  • NEP SS-24B: Two Calrec MADI interfaces, each two-channel (two send/two receive), for a total of four send and four receive from a Sigma.
  • Corplex Iridium: Three MADI-to-router interfaces (three send/three receive); two Calrec MADI interfaces, each two-channel (two send/two receive), for a total of four send and four receive from the Alpha. Note that Iridium uses the MADI highway as its default connection between its Sigma and its Evertz router, so I had to repurpose some of its routing structure. But, with the help of its engineers, this was accomplished with relative ease.

The plan

The goal was to move as many signals around the compound as possible using MADI. We decided that two main streams would be created and designated as Ping 1 and Ping 2. These 128 paths (64 AES pairs) would be where all of the main signals for the tournament would reside, and we filled these streams entirely.

NEP SS-24, the front 9 truck, shipped its course effects via MADI to NEP SS-10C, the back 9 sub truck. The Adder IIs, carrying many of the signals from on course, also resided in 10C. Those signals were also integrated into the MADI architecture to create the bulk of the signals in the streams. All these elements were then sent via MADI to NEP SS-10B, where they were interfaced directly into its router. Once Ping 1 and Ping 2 were created, they were DA'd and sent to the other mobile units for integration into their routers.

Very quickly, we had the four main mobile units all confirming that all the signals had arrived in fine fashion, and the fax went so quickly that I almost missed it. In all the years I have been involved in large remote broadcasts — including Super Bowls, World Series, the PGA, major golf tournaments and AFC Championships — audio setup had never been so ahead of the curve.

Next, we started to establish connectivity on a peer-to-peer basis between the consoles in the mobile units so that the mixers could begin to send and receive the signals particular to their assignments. Everything from course effects mics to dry IFBs, hot mics, mix-minus programs, net return, VTRs and their router outputs were sent back and forth with complete success.

The Calrec console displays an input and output page for MADI, so it was easy to see what was sent and received. Even the mixers who had no experience with MADI picked up on it very quickly and were routing and receiving in no time.

My next focus was to set up quality control in the Corplex Iridium. This would be the place where many of the crucial signals could be shaped and monitored. Because MADI can be DA'd, it's no problem to send copies of the streams to the same place. If you need to send two copies of the 32 AES pairs that comprise the MADI stream, all you need is one additional coaxial cable.

One stream was interfaced with the Corplex router, and the copy was sent to the Sigma audio desk. The router contained the signals that would eventually go to air, and the desk contained the copy that could be used to check signal integrity, without ever interrupting feeds to air. In addition, the Sigma could be used to provide additional copies of individual signals, giving the mixers a level of flexibility and a supply of signals they had never seen before.

Corplex was the origination point for a build of the feeds that went to the international compounds. This was accomplished by using a Cobra Net network. Five rack units were integrated to provide a total of 60 AES pairs worth of signal, which turned out to be barely enough. My experience with Cobra Net has always been positive. It is rock solid, and its ability to move that many signals on a single Cat 5 cable speaks for itself.

What would be ideal would be a MADI interface for Cobra Net. Cobra Net connectivity is labor-intensive, as the physical connections soon reach the hundreds. This results in errors and slow troubleshooting times. The good news is that an interface with MADI is possible and has been put on the table. This would be fantastic, especially if the distro side were MADI and the receive side remained AES so that it would be accessible to end users without MADI capability.


The build was not without some small problems. Initially, one of the MADI-to-router interfaces would not talk to the main streams. We eventually isolated it to a single sync issue. In the end, we fixed the problem with the flip of a switch. In short, on the MADI backplane, there are DIP switches for channel allocation, setting the sample rate and choosing to pass through channel status data in its current state, or force it into a known professional state.

According to the users guide for the NV7512 audio router, forcibly adding common, professional status data is called “Channel Status Striping” or C STRIPE. It is useful in instances where the signal channels have been recombined and the channel status data may have been corrupted. If the sample rate of the MADI signals is being changed, the channel status data is automatically removed, and channel status stripping is applied by default.

It would have been nice to have more of the mobile units in the compound equipped with MADI, but there's always next time. In the end, we broadcast the tournament for five days, and the system remained stable the entire time.

Many positive comments were made about the quality of the audio. I noticed a vast improvement mainly because of the fact we converted our signals to digital early in the process, in most cases before they even left the golf course. Those signals went into Adder IIs and were sent back via fiber to the compound. From there, they were sent to mixing desks and routers and eventually out to MADI streams, never having been downconverted or upconverted.

Another positive result I had not foreseen was that because the mixers were not bogged down by buzz, bad pairs or patching errors, they had more time to concentrate on shaping the signals and the overall management of their other systems. This problem-solving does not end after setup; it is a daily routine for mixers because of many factors and failures within a compound inundated with DT.12 and AES looms, where failures are far more commonplace. The AES looms and DT.12 cables were conspicuously absent. They were down to such a minimum that only a few times during the show did I see anyone outside the trucks working on cabling issues.

That's a wrap

Feedback indicates that the layout we used at the tournament worked well. Everyone involved directly with the MADI had only positive comments for the remote. In short, the use of MADI for bulk audio distribution proved to be a success.

Edward Soltis is the audio supervisor at CBS Sports.