Handling Telephone Calls With Your Audioarts Engineering Radio Console

1. Introduction to Handling Caller Segments

When we talk to customers, one of the topics that comes up with regularity is the handling of telephone calls. How do I connect to the phone system? Do I need a hybrid? Just what is a hybrid anyway? Why is the caller not hearing me? Why can't I hear the caller? What's up with the delay and/or feedback I'm hearing?

The fact is that dealing with telephone callers in the radio broadcast environment is a little different than doing some announcing or playing some music. The object of this paper is to help you, whether you are the installer, operator, or program manager, to gain a little insight and understanding into the somewhat mysterious world of telephone conversation broadcasting.

To this end, we will begin with a discussion of the issues involved in interfacing the telephone world to the broadcast world. Then we will look at some of the equipment involved, and what we expect that equipment to do to help us achieve our goal of being able to broadcast telephone talk. This leads naturally into a discussion of how the equipment is connected, and, of course, how it is operated.

General Issues

Why is there a problem with handling telephone calls in a radio broadcast situation? What are the issues involved? Why is this so hard?

So what are the issues? First, there is the fact that balanced, professional level audio, or even unbalanced, commercial level audio, is not the same as telephone audio. In fact, not all telephone
audio is created equal.

Once upon a time, if you had a telephone, it was connected to a POTS, or Plain Old Telephone Service. Although the days are long gone when we can be so certain, there are certainly still a lot of us connected to a POTS. And that may be what we have in our studio, that listeners will be calling us on.

I suppose that if this was the only kind of system we had to worry about, life would be easier. What else might we encounter these days? Well, there's ISDN, which stands for Integrated Service Digital Network. Since POTS is analog, the key word here is “digital.”

Of course, these days, it's hard to find an ISDN (or POTS) line anymore. Most telephone is Voice over IP, or VoIP. In fact, even when your phone company is delivering you an analog line, chances are it's VoIP until they turn it into analog and hand it off to you.

There are VoIP telephone hybrids that can talk natively to your phone provider and accept analog or digital audio from your console and turn the caller audio into either analog or digital audio for your console to accept.

The purpose of this paper is not to go into great depth about the characteristics of these different types of phone lines, so it is enough to let you know that there are different systems out there.

Interface Problems

There are a myriad of problems encountered in trying to fit the telephone call into our broadcast routine, and we're going to list a few of them here. Once again, the plan is not to go into great detail, but just outline some of the challenges that are faced. Once we've got this under our belt we can proceed to some solutions.

Electrical Conditions

The POTS is an analog system, but the voltages and impedances are not compatible with state of the art professional audio equipment. Voltages of a magnitude that can cause damage to the op-amps used in today's pro audio equipment are present in the POTS. The system is powered from -48V, and the ring voltage, which may be as high as 130 VRMS, rides on this dc offset.

Audio levels are not consistent with pro or consumer grade audio standards. And the phone system is usually limited in bandwidth, unless digital techniques are applied. Line noise may be excessive, especially outside of the limited usable phone system bandwidth.

The phone jack we have access to is usually a 2 wire system, mixing the audio in both directions onto a common path. Part of what the telephone receiver does is to separate the send and receive audio so that we can deal with each separately.

Digital phone systems can address some of these concerns, but they come with their own set of challenges. The various digital formats are not the same as AES-3 audio and thus cannot be directly connected to the console's phone connections, even if the console can handle digital audio.

VoIP is delivered entirely in the IP world until it's converted to analog or AES-3 for your console to accept.

Required Features

We may need to have more than one caller on the line at the same time. And while all callers may be live to air at the same time they usually aren't. Further, we may want the callers to hear each other, a feature known as “conferencing,” or then again we may not.

We may want the caller to hear one thing while we have them live on air, and something completely different when they're on hold. Or not.

We may want to record the callers, or some of them, or none of them.

And we certainly do not want the callers' voices getting back to them, which requires a feature known as "mix-minus" that we'll discuss in a bit.

Solutions

We need to figure out how we can overcome these obstacles. One way to deal with all of these issues is to divide the problem between two pieces of equipment. This is the Audioarts Engineering approach.

We at Audioarts Engineering do what we do best, which is provide the finest in professional grade audio equipment that is equally at home in the broadcast world and the recording studio, and leave the messy details of the physical interface to the phone system to a piece of equipment known as a hybrid, as we will see next.

This paper is mainly concerned with the Audioarts Engineering line of broadcast consoles, and thus console specifics mentioned will revolve around that product line. But many of the discussions in this paper can be applied to the entire spectrum of broadcast consoles and control surfaces manufactured by Wheatstone Corporation.

Do I Really Need A Hybrid?

The telephone hybrid is a device that, on one end, connects to the phone system, and, on the other end, connects to the Audioarts Engineering console. One of the most common calls we get relating to operation with a telephone system is “Do I have to use a hybrid?”

If you are planning to use the fader labeled Caller on your console, there are basically three answers to this question:

1. Yes
2. Most certainly, yes!
3. Let me say that one more time – YES!

Some Audioarts consoles have Bluetooth I/O. If you are going to record a caller using a cell phone via Bluetooth, that may be the only exception to the rule. But when reliability matters on air, use a wired telephone connection and a phone hybrid.

The next question is often “What brand of hybrid should I get?” The answers to this question are numerous, and they all start with the phrase “I don't know - that depends on . . .” The brand and model of hybrid you get depends on several factors, including the type of phone system you have, the need to handle multiple callers, the need to treat callers differently on air than off air, whether you want callers to hear each other, and so on.

Audioarts Engineering/Wheatstone Corporation does not endorse telephone hybrid brands and models. If you're not sure what to buy, contact your favorite broadcast equipment dealer, who will be more familiar with what's on the market today and can help you find something that fits your needs and budget. Please don't ask us in support to recommend a phone hybrid, it's outside the scope of what we do.

Having said that, it's also true that, depending on the console and how it deals with callers, some hybrid features are more desirable than others to search for. We will touch briefly on some of these issues at the appropriate points in the discussion.

What Can I Expect From The Console?

We covered a lot of ground very quickly to get to this point in the discussion. We've now arrived at the good stuff.

The console is, in many ways, the heart of your broadcast facility. Sure, if we made transmitters I'd say the transmitter was the heart, but, really now, the console is the heart of the facility.
If our facility is engaged in broadcast that includes telephone audio as one of its sources, then the console and the hybrid have to play well together. To verify that this will be the case, you need to understand how the two work separately and together. We have already covered the workings of the hybrid, although not in any great depth. We defer explanation of the details to the folks who make the boxes.

Now we will dig into the console in enough detail to make you dangerous.

Consoles Without Dedicated Caller Hardware

First let's consider the minimalist approach. In this case, the console provides nothing special in regard to handling phone calls, but you can still do the job to a limited degree. This is the approach taken with the Audioarts Engineering Air 1. This is also the way it was done before dedicated phone modules were available.

In this approach, caller audio from the hybrid is brought in on a normal console input, and audio back to the caller comes from an output bus that other input modules can be assigned to. Since the caller inputs and outputs are mono signals, some thought needs to be given to the connections if stereo inputs or outputs from the console are used. This will be covered more thoroughly when we discuss the handling of multiple callers in section 4.

In order to have the caller as part of the air signal and also have the caller hear audio from the console, he console must have two output buses available at minimum. One bus will provide the normal air feed and the other bus will provide the mix-minus audio back to the caller. For audio that you want to be on air and also available for the caller to hear, assign that source's channel to both buses. The key thing to remember is that you must not assign the caller input channel to the bus that provides the audio back to the caller. If you forget this you will experience feedback, and not in the good sense.

Multiple callers can be handled with this approach. If you need audio returned to one caller to include another caller's voice, you will need to have a separate bus available for each caller feed, in addition to the air bus. Although this is really a conferencing issue it bears mention here since it impacts the number of callers that can be handled, based on the available console outputs.

Consoles With Dedicated Caller Hardware

Now let's take a step up to a console that provides a special input to handle one single caller. This approach is represented by the Audioarts Engineering Air 4 analog console, the AML Azalea and the Audioarts Engineering DML Series.

In this approach, caller audio from the hybrid is brought in on a dedicated caller input, and a special output sends a mix-minus of one of the standard output buses back to the caller. This approach is generally much easier on the operator than the minimalist approach, since there is no need of being wary of which bus the caller is assigned to, at least in regard to feedback. The caller audio simply cannot be accidentally returned to the caller by any action the console operator can perform, as long as everything is connected properly and nothing is blatantly broken.

The dedicated caller mix-minus can generally be used in conjunction with any of the console's main output buses, and is usually determined by the bus or buses we have decided to assign the caller to. If, for example, we assign the caller to the PGM bus, then the mix-minus back to the caller will be whatever is on the PGM bus, but without the caller voice included. In most cases you can assign the caller to multiple buses in the console1. You should be wary when doing this, since the caller will hear certain sources louder than others if some sources are only on one of the selected buses but other sources are on more than one bus.

2. Handling A Single Caller

Now let's discuss handling a single caller on a console that has dedicated caller hardware.

Getting Caller Audio To The Console

Assuming the hybrid can handle only one caller, the hybrid will have one audio output connection that will feed the caller's voice to the console. The name given to this output may vary from manufacturer to manufacturer, or even from model to model by a given manufacturer. And the characteristics of the audio connection, as well as the connector type, can also vary. You will need to read the hybrid's manual to help you determine how best to make the connection.

You will also, of course, want to read the console manual. If you don't want to read the console manual, read it anyway! But, as far as Audioarts Engineering is concerned, you will always find that the caller input to the console is a professional quality balanced analog connection designed to receive a +4dBu signal. So if your hybrid provides a balanced +4dBu analog output, you only need to connect the two with a good quality shielded pair cable. For the uninitiated, the audio connections will be labeled HIGH (or H, or +), LOW (or L, or -), and SHIELD (or S, or GND, or COMMON). Connecting is always done from HIGH to HIGH with one wire of the shielded pair, from LOW to LOW with the second wire of the shielded pair, and from SHIELD to SHIELD with the outer shield of the cable. The two wires of the pair are usually color coded in some fashion to help you avoid cross-connecting HIGH and LOW.

If your hybrid has an unbalanced audio output, then the connection will be a little different. There are two approaches to take. Ideally, you would use a balun (balanced-to-unbalanced converter) designed to interface the +4dBu balanced professional audio world with the (typically) -10dBV unbalanced commercial audio world. But if that luxury is not available there is a second option. Using the same type of shielded pair cable that we use with balanced connections, connect the hybrid output hot side (typically the center pin of an RCA type connector) to the console HIGH input with one wire of the pair and connect the hybrid output ground side (typically the shell of the RCA connector) to the console LOW input with the other wire of the pair. Then connect the cable shield to the console SHIELD input, and leave the cable shield disconnected at the hybrid end.

Getting Audio Back To The Caller

In the other direction, the console caller feed audio output has to be fed back to the hybrid. On Audioarts Engineering consoles this will always be a professional quality +4dBu balanced analog connection. Once again, the connection at the hybrid end may vary. Also once again, connection is simple if the hybrid has the same +4dBu balanced connection, but if not you are once again faced with two choices. The first choice (need I say once again?) is to use a balun type device. If one is not available, you can still wire things up, but the method you use will depend on the console's output circuit. Rather than try to address the issue in this paper, please refer to your console manual's discussion of unbalanced connection wiring.

Mix Minus

Mix-minus is a topic that befuddles most of us when we're first exposed to the concept, so it begs more discussion than some of the other topics we encounter.
First, think of the term “mix” as it applies to audio. If I have one guy talking into a mic and that's the only thing I'm broadcasting, I don't have a mix. But if I add a CD player, even if the voice and the music don't occur at the same time, I do have a mix. I have “mixed” two signals together and now I have to be aware of how loud one is in relation to the other. That's really simple mixing in a nutshell: balancing the volume of two (or more) audio sources. Sure, there's more to it than that, but for the purpose of our discussion that serves to define the term adequately.

Now the “minus” part – this is where the best of us have stumbled from time to time. The caller should never be hearing his or her own voice coming back over the telephone. This is the very practical consequence of the basic fact that, by the time the caller's voice has reached across the phone lines and gotten into the mix output of the console, there has been a noticeable delay. And by the time that the signal you send back has gotten to the caller's ear, even more time has elapsed. As a result, the caller says something and brief moments later hears a voice repeating the words just spoken. Very disconcerting. And annoying.

For this reason you always want to be sending the caller a mix that is minus the caller's voice.

The mix-minus may be generated in the hybrid, or it may be generated in the console, or it may be done in both places. It's usually not good if it is generated in both places at once if mix-minusing is done by a nulling process. Briefly, if I have audio with a voice and music and I null that audio with audio that is only the voice, the nulling process adds the voice to the mix, but out of phase. If the phase and levels are right, the voice is canceled, or nulled, from the mix, creating a mix minus. But if I assume that the incoming audio is a mix of the voice and the music, and, acting on that assumption, add the voice to the mix out of phase, and further, if the incoming audio actually is a mix-minus already, so that the voice is not present, my attempt to cancel it by adding it out of phase will not cancel it after all, but what I have done instead is to take a perfectly good mix-minus and reinfect it, if you will, with the undesired voice component.

Go ahead and read that last paragraph again if you need to.

Generating The Mix Minus

We've explained the idea of what a mix-minus is in fair detail. What we want to discuss next is some of the approaches Audioarts Engineering has taken to the topic of creating a mix-minus that your hybrid can work with.

One mix-minus method was mentioned above in section 2. This is the nulling method. As inferred, this method takes advantage of the fact that when a signal is added to a copy of itself at exactly the same magnitude and exactly 180 degrees out of phase with the original, the two signals cancel, or null, each other out, and the result is that the signal essentially disappears. The problem with this method is wrapped up in that simple word “exactly.” We can seldom insure that the copy is either exactly the same level or exactly 180 degrees out of phase with the original, especially over a range of frequencies, even the limited range of frequencies used in POTS. Variables such as uneven frequency response and unpredictable circuit impedances play havoc with the nulling process. Thus the nulling technique, although usable in many situations, is not the ideal way to handle mix-minus generation.

Audioarts Engineering consoles do not use nulling to generate the mix-minus.

What we use instead, in most of our analog consoles, is a process that might be called “downstream insertion.” With this method, the caller voice is inserted into the bus signal path at some point after the point where we take the signal off the bus to feed it to the caller. The success of this technique isdependent on a circuit being unilateral, which is to say, in simple terms, that signal flows in one direction but not the other. In the real world there is no such thing as a completely unilateral circuit; this is a characteristic of the elusive “ideal” amplifier. But with modern circuit topologies and components one can achieve a signal path that is very highly unilateral. In practice, this method gives us excellent mix-minus characteristics over the audio range, and is used in the Audioarts Engineering Air 4.

What's In The Mix

Sometimes you may want to know where the caller feed is coming from, i.e., what console bus, or buses, contribute to the feed to the caller. Audioarts Engineering has used a few different methods of selecting the source bus. With the Air 4 consoles, the caller feed is derived from the same bus or buses that the caller audio is assigned to.

Many of the Audioarts Engineering consoles have a feature known as Talkback, and more specifically, Talkback to Studio, that, in some consoles, is pertinent to telephone interfacing as well. In essence, the Talkback (TB) bus is a separate bus to which selected sources can be routed pre-fader and pre-on. In some of these consoles the TB bus is also available as a caller feed source, to be used to talk to the caller while the caller is not on air. The big variation is in what sources can feed the TB bus.

In the Air 4 mic 1 always feeds the TB bus, and no other sources can feed TB.

Other consoles use DIP switches to choose the TB Mic. Consult your console's manual.

Off Air

With a single caller, what are we likely to want to do when we are off air?2 Certainly the host needs to be able to talk to the caller. This often (but not always) implies that the host is not talking on air at the same time. Possibly we want the caller to also hear a song that's playing, or a segment giving clues for a contest, or some such audio that is on the air. And we certainly want the host to be able to hear what the caller is saying.

A common feature in Audioarts Engineering consoles with dedicated caller handling is an off air intercom of sorts, selected by a button that has been variously labeled SETUP, COM, or CUE.
Typically, when this button is pressed, the caller audio appears on the console cue speaker, allowing the host to hear the caller. At the same time, provision is made so that the host can talk to the caller and/or play an audio segment for the caller to hear. The mechanism varies from console to console.

Sometimes a bus is available that can be assigned to on a pre-fader, pre-on basis from input modules, thus allowing the host mic to be available on that bus even if the input handling that mic is turned off and the fader is all the way down. In this case the bus is usually routed to the caller by pressing a bus assign button or a dedicated "caller feed" button. In other consoles, an internal talkback bus having the host mic and, possibly, other sources, is routed to the caller. The DML Lyric and Verse use PGM 3 to create an offline mix fed to the caller when the caller fader is turned off; when the fader turns on it switches to a mix minus of PGM 1.

See your console's manual to see what mixes are available.

On Air

When the caller is on air, things are easier. If the caller is feeding PGM and the host is listening to PGM, the host hears the caller. And if the caller feed is set up to be a mix-minus of PGM, then the caller hears the host. Mission accomplished.

Recording

Sometimes we want to record a caller segment for later air play, or for archival purposes. One approach is to use an otherwise unused bus, such as AUX (assuming such a bus exists in the console). We can assign the sources we want to be recorded, such as the host, some music, and, of course, the caller, to this bus. Then we simply feed the bus output to the recorder.
One problem with this approach is that we may not get an ideal mix of caller voice against the rest of the recorded material.

3. Two Callers, One Caller Channel

This section asks the musical question, “What do I do if my console only handles one caller, but I need to handle two with it?” We will frame our discussion around the idea of handling two callers with a console designed to handle one, but the same approach can be further extended, both in terms of adding more than one caller, and also in adding to a console that has provision for more than one caller to start.

Basically, the idea is to combine the console's dedicated caller capabilities with the minimalist approach outlined in section 1 by using a normal console input to handle the second caller.
As for handling more than two callers, you may have a hybrid that handles the required number of callers, or you may have to use multiple hybrids. In either case you'll need to apply the appropriate techniques, as already discussed, based on a thorough reading of the equipment manuals.

A Simple Example

Caller 1 is brought in on the dedicated CALLER input. The audio from the hybrid goes into the console's CALLER input and the audio to the hybrid comes from the console's CALLER output. The caller hears program minus themselves. The Caller fader is placed in PGM 1 and PGM 2. Mission accomplished.

Caller 2 is brought in on a line input fader, with the audio connected to the left and right channels, and this fader is in PGM 1. All faders other than the one Caller 2 is wired into are placed in PGM 1 and PGM 2. The output of PGM 2 is wired to the hybrid for Caller 2. Because all faders other than hybrid 2's input are in PGM 2, the caller will get a proper mix minus and hear program minus themselves. Because the second hybrid is in PGM 1, they are both on air and sent to the other caller.

Most importantly, because they have separate mix minuses, the callers can hear each other, which is critical when you have a guest on Hybrid 2 and listeners on Hybrid 1 asking them questions!

4. Summary

Handling caller audio in a radio broadcast situation introduces challenges that are not present in the simple broadcast of a DJ playing some tunes. But those challenges can be overcome with the right equipment and some basic understanding of how to use that equipment.

Hopefully we've given you some ideas of how to make that happen with your Audioarts Engineering console.

If there is any concept to take away, you always want to feed a caller program minus themselves, so whether your console has built-in mix minus or it has simple mix buses, ensure that the caller doesn't get their own voice looping back at them.

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