Radio Consoles

IP Audio Networking


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Wheatstone for radio: You know what they say about radio and silence. Right. So don’t even go there. At Wheatstone, we know you have one thing and one thing only that’s going to raise you above the din of today’s multimedia world. Your sound. If it’s just pictures you want, that’s not us. Wheatstone is all about audio. We process it, route it, and cue it up for you. We get it to do stuff that only radio can fully appreciate, starting with audio IP routing (AoIP) that thinks like you do and radio consoles that are the everyday workhorses of thousands of radio studios today. Cool consoles and mixers. Intelligent audio IP studio networking or TDM routing. AM and FM on-air processors that rock. It’s all right here.

Click to download our NEW RADIO PRODUCTS FOR 2015 Brochure

No BS Guide to Radio Podcasting

PODCAST ARTICLE_IMAGE_1500Amateur podcasters can call them what they want, but between us broadcasters, we know those so-called subscribers are really listeners with earbuds and a cellphone.

And that means we can reach them like we usually do -- through their ears.

No one knows those ears better than broadcasters. We know about good content and good sound. What’s new to us are the codecs and the listening environments and devices used for podcasts. To explain what it all means, we asked our audio pros Jeff Keith and Mike Erickson to give us a quick sound check on podcasting.

Oh, the places they go, the things they do

The iPhone, Android and other smartphones are skewed to the vocal range for obvious reasons. Subtract from this equation the codec bit-rate reduction needed to get that sound to those earbuds, not to mention all that background noise your listeners are subjected to while listening on the move, and there’s no way you should hand them a full dynamic range of sound.

Removing program content that can’t be heard by these devices will improve the subjective quality of your audio. Jeff suggests that anything below 100Hz and above 12kHz won’t be missed. In fact, he says, “Removing those frequencies might actually help your sound, due to reduced or removed ‘codec teasers’ such as hiss or hum.”


For all those other unwanted frequencies that happen during pauses in programming or when the AC kicks on during a recording, you’ll need a noise gate same as any other program production. Any good mic processor (such as our M1, M2 or M4-IP mic processors) should have a noise gate to keep the noise floor from rising during pauses in vocal content. This, too, will give the codec less nonsense to work with and turn into noise.

Processing to the codec

Unlike processing your on-air signal in which modulation control is the goal, processing for podcasting is all about controlling what the codec sees. This is why it’s important to give the codec consistent levels and a balanced left and right, especially at lower codec bitrates. Jeff recommends switching from stereo to mono for podcasts at bitrates less than 48kbps in order to preserve audio quality. The ideal is to maintain consistency going in, although often some audio processing can be helpful to smooth out level variations than can cause the codec to overwork. Avoid overly boosted highs, any noticeable hiss or hum, and distortion due to badly clipped audio, all of which adds to the codec’s work (and bit) load.

Adding a trace of AGC or compression can add a measure of “presence” to a podcast, but careful. Keep in mind that many of your podcast listeners will be listening in on headphones, and too much compression this close to the ear could cause fatigue. Others will be listening to longer form podcasts through their sound system in the car, all the more reason why processing that isn’t fatiguing is important.

How aggressive should you set the processing for podcasting? Mike says just enough to raise the audio above any ambient noise for listeners who don't have noise cancelling headphones, but not so much that you remove all trace of quality for those who are downloading low bitrate podcasts.

Most any audio processor that you have in the chain will work. But if you have a choice, use a processor like our Aura8-IP processing BLADE (which has eight separate multiband processors, one of which you can use for podcasting). It lets you selectively add AGC, compression or limiting by bypassing the other sections, rather than require all three functions to operate interdependently. This selectivity makes it a little less tricky to get the right amount and type of processing needed.

For more information on processing for the Internet, download Jeff Keith’s white paper, "Audio Transfer Through the Internet." Wheatstone also introduced a new Audioarts console (our new Audioarts 08 has USB and balanced or unbalanced stereo mixing bus) made for podcasting that is worth checking out if you plan to set up a separate sound booth or studio for podcasts.

Clocking In with ACI

WheatstoneVClock BIGOur Kelly Parker ran across VClock made by Voceware recently, and thought it was pure genius. There are plenty of virtual clocks that are merely numbers on a wall, or virtual clocks that are designed specifically for one broadcast group only. This virtual clock is different. VClock is flexible like a certain audio network we know, so it can transform from just a single clock to a network of clocks taking in information from different sites. Everything on it is configurable, complete with up to 32 lamps that are changeable and can be turned on / off or made to flash with external triggers (such as a "mic live" signal from a mixing console or a phone call). This clock also has an embedded web browser, which allows you to show any content that you like on VClock, simply by creating a web page.


Of course, one thing led to another, and VClock is now one of our third-party add-ons that communicate to the WheatNet-IP audio network through the ACI protocol. That is, from any control panel, workstation or control surface in the WheatNet-IP network, you can trigger salvos within VClock that change its features. VClock interfaces directly into the port of an I/O BLADE access unit through ACI for IP connectivity to our SLIOs.

ACI is our control interface used by automation companies like ENCO, OMT Technologies, RCS and WideOrbit to tightly integrate WheatNet-IP audio networking with automation functions.

Wheatstone has more than 50 technology partners.

For more information about VClock, visit .

ACI: It’s Wheatstone’s DNA Needle and Thread

ACI STORY_1000We have built into all of our audio processors a control protocol we call ACI, for Automation Control Interface. ACI is how Belar’s FMHD-1 with new ADC algorithm tells our audio processors what corrections need to be made for a consistent and seamless HD blend to analog whenever HD Radio coverage is less than robust.

ACI operates over the locally connected network via TCP/IP and can touch any parameter on the processor, whether it's a setting for the diversity delay, recalling a preset, changing input sources, modifying output levels, or even lowering just the AGC band three threshold by 1.62dB during some externally triggered event. Most of the program automation systems can also talk ACI, as can our console surfaces, so ACI brings new possibilities to our audio processors as well as WheatNet-IP system.

From St. Cloud to Grand Forks, Leighton’s Dream Studios

There’s a lot of that going on here, from the usual satellite relays to the calls on-hold and lobby P.A. systems that are part of the WheatNet-IP system. (They put the phone system and lobby speakers on WheatNet-IP, and the NexGen automatically changes the station every hour for waiting guests. Cool.) They’ve even engineered the WheatNet-IP to unlock the doors in the morning. “We have programed soft keys on the consoles to unlock doors for early morning guests through the I/Os on the BLADEs,” said Tony Abfalter, DOE for Leighton.

View the embedded image gallery online at:

Life on the EDGE: STL via IP Microwave

WheatstoneIP STL Splash 300Any wireless IP microwave system will work as an STL, just as any camera (or phone) can take a picture. But as to how far and how robust, and for how much, that’s when the picture starts to get a little fuzzy.

There’s licensed versus unlicensed systems. Part 101 versus Part 15. Full duplex or half. Matters of throughput, range, delay and buffering, and where to install it and with what – it’s all-important in the wireless IP world. And certainly there’s cost, which can start at $500 for a basic unlicensed-frequency wireless IP system complete with radios and dishes and run up to $30,000 for a licensed-frequency system, depending on how far, how fast, and how reliable you need that link to be.

Systems vary, but they all have a few basic advantages.


High-speed Bidirectional IP Data Throughput

When you put up an IP link from the studio to the transmitter, your transmitter site immediately becomes part of your Ethernet network. Audio from a WheatNet-IP audio network I/O BLADE or EDGE unit connects directly into the IP wireless radio through RJ-45 connectors, and because it’s all IP, that means you can carry audio, video, voice-over-IP, and data of all kinds. Back and forth. Both ways. If you have video surveillance at your tower site, you can carry that data back. If you have a Burk or other transmitter remote control system, you can carry that data back. And, if your transmitter is remotely located with spotty or no cellphone coverage, you can put VoIP out there and carry that back and forth over wireless IP. Your remote tower site is now part of your network, even though it’s miles down the road.

Wireless IP systems can go some distance, too. “Our longest shot on wireless IP microwave is 55 miles,” says Jeff Holdenrid, who specializes in wireless IP for broadcast and other emerging markets for DoubleRadius engineering firm. Jeff has installed dozens of wireless IP microwave systems with our WheatNet-IP audio network in the past five years, most averaging in the 20 to 25 mile range.

The make or break rule is, as always, line of sight.

As for throughput, IP microwave has plenty of that, too. For example, a WheatNet-IP audio IP-88D BLADE into an IP wireless radio can run 8 stereo channels across a wireless IP link and still have enough bandwidth left over for all those things we just talked about: video surveillance, VoIP, remote control and other periphery functions.

Edge-Flowchart 2560Licensed Versus Unlicensed

Your choices are generally 5.8 GHz unlicensed wireless IP systems or licensed wireless IP systems in the Part 101 band, usually 6 GHz or 11 GHz (18 GHz and 23 GHz under Part 101 aren’t all that practical for ranges beyond one to two miles). Licensed systems are generally full duplex, whereas unlicensed wireless IP systems are almost always half-duplex.

The former has the obvious benefit of a licensed frequency as protection against someone using and interfering with that frequency for their purposes, but the latter can be useful, as well.

IP wireless systems operating on the unlicensed band often make a good option as an affordable backup STL. They’re also priced low enough to bring VoIP communications to transmitter sites that have limited or expensive cell coverage. “A lot of broadcasters are paying $600 or $1000 a month for their Internet connection to the transmitter site. Other than a tower climb to install the wireless, their return on investment is two to three months compared to paying for a leased line from their provider,” explains Jeff.

One critical difference between unlicensed and licensed wireless IP systems is how the two handle latency. According to Jeff, latency on an unlicensed system can jump from 2 milliseconds up to 12 or 20 milliseconds depending on interference or something as simple as changes in weather patterns. Comparatively, IP wireless radios operating on a licensed frequency have a consistent, lower latency, typically around 100 microseconds.

But there are plenty of uses for unlicensed 5.8 GHz IP wireless systems, especially now that Wheatstone introduced in April a special network unit, the Network EDGE, which has more data buffering built into it in order to handle the latency swings typical of unlicensed wireless IP radios. The EDGE provides the necessary delay as a buffer to any latency shifts that come across the link, which acts as a interface between the WheatNet-IP audio network and the IP radio.

“Unlicensed IP has taken off because for 1,000 dollars you can get a system, and now that the EDGE can hold the clock time consistently, we’ll probably see more applications for these,” says Jeff.

Unlicensed: Distance and Throughput

Although unlicensed systems can go far (the 55-miler that Jeff mentioned earlier is an unlicensed wireless IP microwave), generally you’re going to be trading off throughput for distance. “The biggest unlicensed radios --- like the Airfiber by Ubiquiti – have a shorter range and you can pull 700 megs out of them in a perfect world scenario (half-duplex),” says Jeff. But with licensed, he adds, “We can stack up greater than 2.5 gig.”

If you’re considering an unlicensed system, features like interference mitigation will be important. “In the 5.8 world, there’s the signal to interference ratio – how much noise it can take before the link drops. Some of these products have interference mitigation, where they see the frequencies all the time, so if someone puts something up on your band, it jumps to the best frequency it can perform on. If you’re considering unlicensed, that’s going to be a big product differentiator,” says Jeff.

Whether you decide on licensed or unlicensed, you’ll need IP wireless radios and microwave dishes on each end of the STL, and a good surge protector. For more information on WheatNet-IP and IP microwave STLs, contact your Wheat sales team.

Next month in Wheat News, we’ll explore licensed IP microwave systems.

Jeff Holdenrid is a senior sales engineer with DoubleRadius. He can be reached at 866-891-3602 X185 or by email at This email address is being protected from spambots. You need JavaScript enabled to view it..

Super Duper Mic Processing

96K VOICE_PROCESSORS_2560In the M1, M2 and M4-IP mic processors, the A/D converters and all the processing run at 96kHz (or 88.2kHz in a 44.1kHz context). This is done for three reasons:


  1. Reduced latency. This is the time delay through the processor, end-to-end. An unfortunate aspect of digital systems is that such delays are endemic and cumulative, so any opportunity to reduce them must be seized. It is particularly crucial where presenters are involved: any significant delay can be seriously disturbing to them, and even short delays can produce comb-filter coloration when the talent's own voice, heard via bone-conduction, mixes with the headphone audio. This colors their perception of what they sound like. Mess with an artist's self-perception at your peril. In short, running at a super-rate halves the conversion times - the major source of latency in a processor - shaving a big chunk off the delay.
  2. Improved high-frequency EQ. Not generally appreciated outside the lab is that the top octave (say from 10kHz on up) in a 48kHz system is dominated by the tyranny of inevitable “zeroes” (notches) at 24kHz, half the sample rate. These zeroes affect the calculation for and accuracy of digital filters in this upper range, taking some questionable heroics to beat them into acceptable sonic shape. Alternatively, running the EQ at 96kHz blows right past the problem (the nettlesome top-octave is now in inaudible-land). Subsequent reduction to 48kHz does not meaningfully affect the now wholly accurate EQ characteristics.
  3. Accurate dynamics behavior. Certain spot frequencies (sub-multiples of the sample rate) can suffer serious detection inaccuracies, particularly with peak-sensing detectors found in limiters or fast compressors. In some cases, such as a protection limiter, these can even render the device useless. Running these dynamics at super-rate forces the worst of these “black holes” an octave up and generally out of harm's way, with any remaining stragglers far easier to contain.

These three results of high-rate processing confer obvious operational benefits and superior sonic performance. An adjective commonly used about the M1 or M4-IP's sound is “sweet.” High-rate processing is a large part of the reason.

Here’s some other stuff you probably didn’t know about Wheatstone M-1, M-2 and M4-IP mic processors.

Gigabit Ethernet. Just the Facts.

Gigabit LargeNumbers don’t lie. That’s what your friendly police officer will tell you when he clocks you going 70 in a 35 mph zone. But, this isn’t entirely true when it comes to the speed of Gigabit Ethernet networks.

Most of us assume that Gigabit Ethernet links transfer data at one gigabit/second, or 10 times faster than 100Mbps Fast Ethernet.

But, in fact, a Gigabit Ethernet cable contains four twisted pairs of wires that are each clocked at 125 Mbps. What the "Gigabit" actually means is that a gigabit of information (data payload plus overhead) can travel across the cable in one second. Because of the efficiency of the modulation scheme and the use of all four pairs in both directions, instead of a pair each way as is the case for Fast Ethernet, Gigabit Ethernet is effectively 10 times faster than 100BaseT (Fast Ethernet).

At an order of magnitude improvement over Fast Ethernet, Gigabit Ethernet allows the audio network to deliver many more packets that much faster and therefore mitigate some issues.




The Gig on Latency

Take latency. Latency in an IP audio network is the delay between when audio enters the system and when it comes out. Every audio network has some latency because it takes a small but measureable amount of time to take analog audio in, convert it to digital, construct the AoIP packets, transmit them across the network and then reverse the process at the other end. In any IP system, the transit time across the network of an individual piece of data is not guaranteed or predictable. Ethernet networks are designed to avoid data collisions (which happens when different bits of information try to occupy a wire at exactly the same time) by squeezing out packets in between other packets in a multiplexing process controlled by the network switches. You just don't know when "your" packet is going to get there. The IP audio network deals with this by using temporary storage in buffers on each end. It fills up a pool of information on the transmit side so there is a ready source of data whenever the switch is ready to send a packet. Likewise, it fills up a pool of data on the receive side so there is enough data to carry you over the breaks when the network is busy sending someone else's packets.

As long as the transmit and receive buffers fill and drain at the same rate there is no interruption in final data delivery. The buffers absorb the variance in packet delivery. The catch is that for this scheme to work, the buffers are designed to be half full of data on average, so as to be deep enough that the data in the buffer never runs out or overflows during the worst-case variance in packet timing. This means that the receive data can't start playing out until its buffer is half full or the scheme won't work. The length of time it takes to fill the initial buffer half full is a main part of latency.

What does this have to do with Gigabit Ethernet, you might ask? Just about everything, actually.

Because a gigabit link is 10 times faster with 10 times the throughput of Fast Ethernet, packets can get to their destinations faster. Furthermore, the large capacity of the link allows for many more packets to traverse the network without risk of congestion and collisions and delays by the switches trying to find an opening on the wire for a packet. Because there is less concern with congestion, packets can be made smaller and more of them can be sent more frequently. Thus, buffers can be smaller and therefore, latency can be decreased. On the flip side, less link capacity often means larger data payloads, which can be necessary to ease congestion in lower bandwidth environments but at the unfortunate expense of increased latency.

Big Capacity

From the system perspective, the capacity of a link is all-important. As advertised, Gigabit Ethernet can reasonably handle 10 times the capacity of Fast Ethernet. For example, whereas you might push the upper limit of your Fast Ethernet link at 16 stereo audio channels, a Gigabit Ethernet link will be able to easily do 160 stereo audio channels.

One hundred sixty audio channels might seem like overkill in your studio, however it doesn’t take long for signals to add up. The more you ask of your audio network, the more it will need capacity to handle busses and foldbacks, backup sources, mixes, and headphone streams -- not to mention control and monitoring signals. If you want to automatically switch between live assist and dayparts, for example, that takes something like a utility mixer (which is part of our WheatNet-IP BLADEs) to switch them at the right time and level – plus the capacity to handle that switching. Put a few I/O devices in a studio and pipe their audio over a link to your rack room and the channel count goes up quickly.

It’s a given that you will probably need to run more than 16 audio channels through a link at one time. Any time you add more capability onto the system beyond a basic input or output channel, that’s when you need capacity. It’s also nice to have enough of it available for when you want to add something like an audio clip player or multiband audio processing to a network I/0 unit (which we did recently with the introduction of our new BLADE-3 I/O units). Having the available channel capacity allows us to add in the new features and functions that enhance the power and flexibility of the system without running out of network resources.

There’s also the flip side of capacity, or what happens when you run out.

As you add more channels to a link, the possibility of dropouts is increased until they are commonplace and you hear them routinely. It’s a logarithmic function up to the final cliff, not linear.

In fact, there’s a lot at play in the audio network that affects the quality of the end result. IP audio networks are highly stressed, running much more traffic than initially expected. That’s why it makes sense to use a topology (Gigabit Ethernet) that is more tolerant of the workload IP audio puts on it.

For example, the bigger the switch capacity, or what is referred to as switch fabric, the more packets it’ll be able to move. Just as on the Ethernet link itself, IP audio network switches should be sized and configured to handle the amount of traffic you're going to throw at them -- both today and five to 10 years from now when you'll ask your system to handle the new features we haven't even dreamed about yet.

By using Gigabit Ethernet links and switches you'll have the highest capacity, lowest latency, most future-proofed system available today.

Cruising Main Street

Beasley2Beasley’s new WheatNet-IP remote studio near historic Las Vegas’ Fremont Street is a modern throwback to the days when listeners and artists could walk into any radio station on Main Street with a request or a record album.

“It’s sort of like being back in high school again when everyone cruised (downtown) Fremont street with their radios turned up,” says Tom Humm, who was raised in the area and is now the Vice President and Market Manager for Beasley Media Group, Las Vegas.

The new Beasley Media/Cox Business Broadcasting Studio built for Beasley Media Group’s five Las Vegas stations sits adjacent to a busy amphitheater in Downtown Container Park, the area’s newest shopping and entertainment center constructed of cargo containers stacked on top of each other. With the help of a fiber optic communications link sponsored by Cox Business and our WheatNet-IP audio networking, the group can seamlessly link its new remote studio to its main studio on Durango Drive some 15 miles away.


“It’s one-button control. It’s all done through (WheatNet-IP) routing, so they can go live very easily and at very high quality,” says Mike Cooney, VP of Engineering and CTO at Beasley Broadcast Group.

Beasley3“The point-to-point fiber connection puts it right on the WheatNet network in our studios, so this studio just becomes another studio like any studio in the (Durango) building,” explains Beasley Las Vegas Regional Engineering Manager Lamar Smith, who used Wheatstone’s new Screen Builder app to quickly customize a touchscreen interface on a large flat screen that acts as a control surface in the new remote studio. Beasley’s main studio operation on Durango Drive is a WheatNet-IP facility comprising LX-24, E-6 and E-1 control surfaces and more than two dozen I/O BLADEs.

And, like early radio, the new studio brings back that main street accessibility to music and entertainment for which radio is known, but with all the modern conveniences. In addition to fiber optics and audio IP networking, the new remote studio sponsored by Cox Business includes a bank of phone chargers for use by the public. Recently, on Star Wars day (May the 4th be with you), fans were able to re-charge their iPhones and Androids while walking around the park dressed in costumes as part of a Beasley event commemorating their big day with contests and prizes.

“We’re definitely bringing life back to downtown. We did our first-ever adult Easter egg hunt here as a remote broadcast, even before the studio was finished. We invited 300 people and we had 4,500 people in line before 9 o’clock, so I guess that’s a pretty good indication of how alive local radio is here,” commented Humm, whose career in Las Vegas radio has spanned more than four decades, including radio’s heyday in downtown Las Vegas.

Beasley6Beasley’s own KDWN-AM as well as KENO-AM and KGIX-AM were located on or near downtown Las Vegas starting in the 1940s, but like other stations across the nation, they abandoned their downtown studios as part of urban sprawl and began relying on remote vehicles for live coverage of local events.

Beasley Media Group Las Vegas owns NewsTalk 720 KDWN-AM and four other stations: Classic Hits 96.3 KKLZ-FM, Vegas’ New Country 102.7 KCYE-FM (The Coyote), Old School 105.7 KOAS-FM, and Star 107.9 KVGS-FM.

Downtown Container Park’s inaugural year brought in more than one million visitors and welcomed artists such as Sheryl Crow, Cults, Belmont Lights and Cayucas – a venue now on tap by Beasley’s five local stations, thanks to the new studio.

Construction for the new studio began in February and its completion happened to coincide with the NAB convention held last month and attended by more than 100,000 people from around the globe.

Beasley Media Group owns and operates 53 radio stations (34 FM and 19 AM) in twelve large- and mid-size markets. It is the oldest continuously managed, publicly traded, pure play radio broadcaster in the country.

IP Consoles 101

SUNY 2560sShown is web radio OWWR’s number-one studio with IP-12 control surface, M2 dual mic processor, and just the right amount of WheatNet-IP audio networking. We love the baby-proof covers on the Tripp-Lite power module! We don’t envy guys like Joseph Manfredi, who has to explain control surfaces to a group of new students every year as a faculty member in the American Studies/Media & Communications department and the Station Manager of OWWR, Old Westbury Web Radio, at the SUNY College at Old Westbury, New York. “I’ll never convince them that there’s nothing under that fader,” says Joe, referring to the station’s new IP-12 control surface.

Joe has four studios that he teaches out of and streams 25 live shows from weekly, the most up-to-date one being his "Studio-A", with the IP-12, M2 dual-channel mic processor and WheatNet-IP audio network that he and Chief Beginner Bob Anderson installed last year. The IP-12 is an ideal entry into AoIP for small studios, providing a self-contained digital audio board with WheatNet-IP audio network BLADE engine for flexible access to sources and destinations. “My ‘yesterday’ studios look and function very well, but this is the one that gets it done,” he adds.


Joe, along with about 80 staffers and students enrolled in the SUNY College at Old Westbury, runs Old Westbury Web Radio (OWWR). The web radio station streams a variety of music, talk and sports programming on, (you can get OWWR through the TuneIn Radio cellphone app), and on-campus through closed circuit cable.

OWWR is a 24/7 operation similar to any radio station with IDs, rotations, PSA's, even live remotes. “We host fundraisers and a concert series every Friday night during July and August, which we stream live online on Ustream with four cameras. I mean, we go in,” says Joe.

He’s continually turning over his staff as new students enter the environment, graduate, and move on. All those things that Wheatstone broadcasters take for granted – dedicated faders for the Tieline remote gear, easy peazy switching between sources, that extra mic input that is sorely needed but difficult to hardwire in the old way – are a big deal when it comes to training students, faculty, alumni, community volunteers and running a 24/7 station. “I like the fact that the headphone knob governs the headphone amplifier and I like how the microphones sound now that they run through the Wheatstone processors,” says Joe.

As for those faders, he says they’re as " smooth as silk," even if his students don’t believe there’s audio there.

Which Switch for AoIP?

IP audio networks are very different from standard enterprise or office networks in almost every way, but none more spectacular than the nature and volume of traffic they handle.

Switches in these networks need to be able to handle large, continuous streams of data.

SwitchesCharts 2560Consider these two graphs that were taken over a one-minute period on two different networks. On the left is a simple office network of 18 PCs doing what PCs usually do – browsing the web, accessing printers, moving files around, and sending and receiving e-mail. You can see that the traffic peaks out at about 144 packets per second, and that the traffic is very “bursty.” Sometimes the network’s very busy, and sometimes it’s relatively quiet. This is typical of most computer networks.


On the right is a graph taken after three audio-over-IP channels were added to that same network. Note that the scale of the graph is different. We have gone from 144 to 25,000 packets per second, which is 173 times the peak traffic we had before. In addition, note that this traffic is steady, not bursty. That high packet rate stays high, and would go even higher if we added more channels. This is what traffic looks like on an AoIP network – very high bandwidth, all the time.

So, when we’re choosing switches for use in our IP audio networks, we look for some definite features and qualities that can handle this traffic load.

First off, the switch has to have a high-capacity fabric, which is the actual mechanism inside the switch that allows it to pass data among its ports. There are a lot of different ways that switches handle traffic – store and forward, cut-through, fragment-free, adaptive switching – but no matter what type of fabric is used, it’s got to be of sufficient capacity to handle full bandwidth traffic without blocking.

Second, the switch has to be able to snoop IGMP packets and switch them appropriately. Otherwise, multicast traffic is going to flood everywhere and poorly impact traffic.

Third, the switch has to be managed. We can’t set up, monitor, or control the switch correctly without this crucial feature.

And finally, the switch has to have enough ports to support our intended use of the switch, preferably with a reasonable amount of room for expansion.

Switches as Audio Routers

Ethernet switches do just what it sounds like they do. They operate at OSI Layer 2, which is the data link layer, and they look at the MAC (Media Access Control) address in every packet's header. The switch builds a table of what MAC addresses exist on what ports, and sends packets to the right ports. This means that even during heavy traffic conditions, each port only gets traffic it's supposed to get and nothing else.

Switches communicate in "full duplex" mode, meaning each port can send and receive at the same time. Each machine on the network can effectively “hear” while it's “talking,” which really speeds things up.

Under the control of the AoIP protocol such as WheatNet-IP, the switch carries out the actual routing and distribution of audio throughout the network. That work might be handled by a combination of core and/or edge switches, in which case they collectively act as your audio router and distribution system.

Which Switch is Which?

There are two basic types of switches: managed and unmanaged. Unmanaged switches are the off-the-shelf, sold-in-a-colorful-box switches that you find at the office supply store. They're generally used for building small, basic networks. These switches don't have the most powerful switch "fabric" (the guts that do the switching), which means they could eventually crash, flood the network with garbage, or both. For this reason, and others, unmanaged switches are not suitable for AoIP networks.

Managed switches come in two flavors: Layer 2, which are the sort of switches you’ll find in the IP audio network world; and Layer 3 switches, which are highly sophisticated IP routers in and of themselves.

Managed switches are professional-grade switches. They have a configuration interface so you can get inside the switch and set various operating parameters. They're designed for environments where reliability and high availability matter. They have advanced features like Spanning Tree Protocol, and Link Aggregation built in. And you can usually monitor them in real-time to see how traffic patterns are shaping up and where your bottlenecks, if any, might be. Plus, they support (at one level or another) IGMP, which is essential in the AoIP world.

IGMP Required

IGMP is the Internet Group Management Protocol, also known as multicast. It's designed for applications like AoIP that send a lot of data across the network. It allows a source to send a stream (an audio channel, for example) out just once, and for receivers or "subscribers" to tap into that stream and receive it.

When a source is needed, a "group" is created and the source is streamed. When a destination needs that source, it sends out a special message and "subscribes" to that group, and it then receives the stream.

The switch remembers these subscriptions and routes packets accordingly, so only ports that have subscribers on them receive the stream.

How does it do this? IGMP snooping. Most Layer 2 managed switches have IGMP snooping, a feature that lets the switch “look” inside packets that are coming from an IGMP group. It "knows" when a subscriber signs up to receive a stream, and stores this information in a table. The switch then allows those multicast packets to go only to ports that are supposed to get them, so that the streams don't flood the network. When the last subscriber on a port drops out of a group, the switch "prunes" that port's traffic. This optimizes traffic on the network and keeps bandwidth usage as low as possible.

Scotts-Illustration WO_MULTICASTHere is why multicasting is such a good idea for AoIP networks. Shown are three PCs that are set up to receive audio from a server. Without multicast, the server creates three streams, one to go to each PC, and sends them out onto the switch. The switch dutifully sends each stream to its intended receiver. But the switch is now handling a lot of packets -- the whole stream, times three. This isn't efficient, and if we multiplied this out, it would become unworkable.

Scotts-Illustration W_MULTICASTMulticast is a much better way to deliver packets in the AoIP network. With multicasting, a single stream of packets leaves the server, carrying the audio. At the switch, the group table says that ports 1, 3, and 5 have subscribed to the group, so the packets are sent to those three ports in parallel. The switch is handling a third of the traffic through its switch fabric, and if another port subscribes, there's really not much of an impact on the traffic overall.

Switch Configurations

In AoIP, as in other kinds of networking, we use switches in two roles – edge and core. Edge switches are generally small, lower-capacity switches. We still want them to have all the features we discussed before, but they’re meant to be placed on the periphery of the network, like in a studio or other area within the facility. We might, for example, bring the control surface, the audio access point, and perhaps a remote button panel into an edge switch in the studio.

We don’t need many ports on an edge switch – just what’s local, plus one or two ports to connect it to the core switch. This has two advantages: one, it concentrates traffic so we only need one or two runs back to the core switch, rather than one for each device; and second, it gives us the ability to operate the studio as an independent “island” in the event that there’s a problem with the core switch.

Core switches are big and centrally located, and represent the nexus of the facility. All of the edge switches connect back to the core switch, which generally lives in a rack room or central machine room. Devices local to that area are also often brought directly into the core switch. Core switches are often made very large by stacking multiple switch units – with Cisco, this proprietary cabling system is called Stackwise®. Core switches can also be designed in such a way that they offer redundancy.

Scotts-Illustration EDGE_v_CORE_SWITCHsHere we see a facility of edge and core switches. You can see the edge switches located in each studio, with all local devices connected to them.

From each edge switch, there’s a run back to the core switch. As you can see, if the core switch were to fail, each studio would still be able to function as an “island.”

Other Switch Considerations

We suggest keeping AoIP networks separated and isolated from normal office / enterprise networks. If the networks are not isolated, each network has the potential to adversely impact the other – the guy down the hall streaming video can occupy bandwidth that the AoIP network needs, and the AoIP network can generate enough traffic to make web browsing and other activities somewhat slow.

You can do this by using a large, managed switch to create a separate VLAN for the AoIP network; provided the switch fabric has the capacity, this is fairly safe. However, since you might not have full control of that switch if it’s “owned” by the IT department, we generally prefer to see physical separation of the networks, i.e. not sharing any hardware or infrastructure at all with an office network.

Overall, switches are integral to a larger AoIP ecosystem that includes WheatNet-IP I/O BLADEs, control surfaces, NAVIGATOR software and scripting, talent stations, and processing.

Cris Alexander On Technology Disconnect

thumb ChrisStory 2000bYou know that big disconnect where you have new technology on the way in and old technology on the way out, and a budget that doesn’t quite cover it?

We’ve all experienced awkward technology transitions. But there are some engineers, like Cris Alexander, the DOE for Crawford Broadcasting, who seem to manage these better than most. Cris has been using Wheatstone consoles and network systems since at least 2005, when he purchased our TDM router with G-6 consoles. He’s been known to get a budget to stretch like taffy across five major markets and several decades of technology.



We asked him for a few tips and got back these useful Cris-isms:

Reuse, recycle, reclaim. His solution for the big disconnect between existing TDM technology and newer IP audio networking is classic green economics: bring the most dated studios up to current technology using network hardware that can be repurposed.

Until this past fall, the three production studios for the Denver cluster were all analog. Updating these to new Wheatstone surfaces with WheatNet-IP audio network was a no-brainer. But deciding how to connect them to the four on-air studios and the newsroom that would remain with TDM routing for another five years required some strategy. “We thought about using a MADI card to bridge the WheatNet-IP with the TDM router in the interim, but we’d never be able to get the useful life out of it,” he said.

Instead of MADI, Cris tied the two systems together using the I/O in a standard BLADE access unit that could be reassigned to another studio or part of the network once the facility went AoIP throughout. “MADI for us was life limited, whereas the (WheatNet-IP) BLADE I/O unit could bridge the two easily and cost-effectively, and still serve a useful life after we converted everything to WheatNet-IP,” he explained.

Extend the life of what you have. Cris isn’t in any rush to replace the cluster’s Wheatstone TDM Gibraltar network, however. “It still works and looks like new, is in excellent condition and has years left on it,” he said of this TDM workhorse that remains in the four main studios and newsroom. Just recently he replaced the hard drives on the routing system, which reset the depreciation clock back to almost new and will give him at least another five years of useful service out of the system -- or more. “Actually, we could probably keep this system for another ten years,” he added.

Get same in upgrades. His TDM routed studios have G-6 console surfaces. When it came time to upgrade the production studios to WheatNet-IP, he looked for – and found – the IP equivalent that would give his talent the same feel and function they were used to in the G-6 console. “The E-6s were very similar and we even got the classic style E-6 that matched the appearance of the G-6s. It makes all the difference in bringing together the facility,” he said.

But get the best. In almost all cases it is best to go with the latest generation of equipment if you can afford it, according to Cris. For high-availability access points in the new AoIP network, he went with WheatNet-IP BLADE-3 I/O access units rather than the second-generation equivalent in order to gain a few helpful features that will reduce acquisition costs in the long run. For example, while second generation BLADEs had removed outboard DAs from the balance sheet because of built-in utility mixers, stepping up to third-generation BLADEs at certain access points gave him this, plus audio processing at these access points that will eliminate outboard processing in many cases – and contribute to a better sound overall.

Incidentally, for the access points that use second-generation WheatNet-IP BLADEs, Cris made sure to upgrade their CPU software in order to squeeze every ounce of performance and usability possible from these I/O units.

Look ahead for any disconnects down the road. This is where product design and technology standards in general can make a difference. For example, Cris likes that Wheatstone’s WheatNet-IP BLADE-3 I/O units are AES67 compatible, a standard that Wheatstone engineers helped ratify in 2013 as part of an industry effort to provide interoperability between systems and equipment. “That’s just another thing that helps future-proof our radio stations,” commented Cris.

Once you’ve perfected your approach, duplicate it. Cris tests and perfects new technology transitions at the group’s Denver cluster, where he’s located, and then rolls out the proven results to Crawford’s four other clusters in major markets. There are several new BLADEs and E-6 control surfaces on the way to him as we write this, all of which will be used to upgrade Crawford stations in Detroit, Birmingham, Chicago and Los Angeles.

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