WHEAT:NEWS Volume 6, No. 4

Wheatstone Sign 250w

Well, another NAB is in the can, and we're back in New Bern with lots of activity planned for the next few weeks. We'll be seeing some of you at Broadcast Asia! But meanwhile, back at the ranch, it's time for yet another issue of WHEAT:NEWS.

This month, we'll have most of the content of a paper that one of our engineers delivered at NAB this year: which Ethernet switch should you choose for use on your AoIP network? We'll audit "IP Consoles 101" with Joe Manfredi at SUNY College. We'll look at what Beasley is up to in Las Vegas, and we'll find out why high sample rates are an important feature inside a digital audio processor. 

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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.

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 owwrny.org, (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.

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.

Have Your Eventide Delay and Network it, Too!


Eliminate one more network box in the studio chain. Eventide’s BD600W delay unit is now available with an optional WheatNet-IP network card for easy and seamless integration of profanity delay into the WheatNet-IP audio network.

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.

Video: Can't Go Back

Remember those Lincoln commercials with Matthew McConaughey? In this short video inspired by that campaign, we hear some reflections on the nature of TV audio in a similar vein. Produced by Scott Johnson and featuring actor Allen Andrews and a certain special guest you'll probably recognize. #wheatnet



  • WRAY-FM (Princeton, IN) purchased four IP-12 control surfaces. 

Impact Partnership (Kennesaw, GA) purchased new NAVIGATOR software for an existing WheatNet-IP audio network.
  • Media Engineering (Switzerland) purchased two new Network EDGE units.
  • Ramar (Lubbock, TX) purchased the Screen Builder app for an existing WheatNet-IP network.
  • KATB
-FM (Anchorage, AK) purchased an E-1 control surface.
  • MediaWorks (Auckland, New Zealand)
 purchased two LX-24 control surfaces and WheatNet-IP BLADEs. 

  • Crawford Broadcasting (Birmingham, AL) purchased three E-6 control surfaces.

iHeartMedia (Cincinnati, OH) purchased an L-12 control surface.
  • Entravision (Los Angeles, CA) purchased an LIO-48 high density BLADE for an existing WheatNet-IP system.
  • Radio 1 (Mexico City, Mexico) purchased an E-1 control surface.
  • RTÉ (Dublin, Ireland) purchased an IP-12 digital audio console.
  • IMG College
 (Winston-Salem, NC) purchased three LIO-48 high-density logic BLADEs for an existing WheatNet-IP audio network.
  • iHeartMedia (Grand Rapids
, MI) purchased three LX-24 control surfaces.
  • iHeartMedia (Birmingham, AL) purchased three I/O BLADEs for an existing WheatNet-IP audio network.
  • South Carolina Educational TV (SCETV) (Columbia, SC) purchased a Dimension Three TV audio console.
  • Purdue University (Fort Wayne, IN) purchased a Series Four TV audio console for its TV production curriculum.
  • Tribune’s WITI-TV (Milwaukee, WI) added another E-6 control surface to an existing WheatNet-IP audio network.
  • Russia Today (Moscow) purchased two LX-24 control surfaces.
  • Beasley Broadcast (Philadelphia, PA) purchased an E-1 control surface.

Audioarts Engineering

  • Townsquare Media’s KRFO-AM (Owatonna, MN) purchased an Air-4 console.
  • WOOC
-FM (Troy, NY) purchased an Air-4 console.
  • Radio Brazil purchased fifteen Air-4 consoles.
  • Crawford Broadcasting’s WCDX-AM (Rochester, NY) purchased a D-76 console.
  • City of Monona (Wisconsin) purchased an Air-4 console.
  • KUZZ-AM/FM (Bakersfield, CA) purchased an R-55e console.

Wheatstone Audio Processing

  • Cornerstone Broadcasting (Port Orange, FL) purchased a VP-8IP multi-mode audio processor. 

  • WBGW
-FM (Fort Branch, IN) purchased a M2 dual channel mic processor.
  • KWWK-FM (Rochester, MN)
 purchased an FM-55 audio processor.
  • CBS (New York, NY)
 purchased an M2 dual channel mic processor.
  • Entercom (Wichita, KS) purchased a VP-8IP multi-mode audio processor. 

  • Blue Sky Broadcast (San Diego, CA) purchased an M2 dual channel mic processor. 

  • Educational Media Foundation (Omaha, NE) purchased a VP-8IP multi-mode audio processor.