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Your PPM Boxes Have Arrived. Now What?

Broadcasters in markets using the Arbitron PPM electronic ratings system must develop systems that can reliably detect encoding problems as soon as they occur and that will immediately notify technical responders of trouble.

(click thumbnail)Greater Media’s Larry Paulausky discusses the Arbitron PPM during the NAB 2008 BEC. Photo by Jim PeckWhat is worse than being off the air? Having a problem with Arbitron Portable People Meter encoding.

Why? Because if you’re really off the air, someone is going to tell you; but if you aren’t PPM encoding, you won’t find out until the next ratings period!

Broadcasters in markets using the Arbitron PPM electronic ratings system must develop systems that can reliably detect encoding problems as soon as they occur and that will immediately notify technical responders of trouble.

The PPM system requires broadcasters to place Arbitron-supplied encoding boxes in the audio air chain of each program stream. The encoders analyze the program audio and opportunistically add a subaudible coded message to the content. The message uniquely identifies the program stream and includes a timestamp. Portable pager-sized listening devices carried by survey respondents recover the codes.

Beginning in the spring of 2007, Philadelphia was the first U.S. market to “go live” with official published audience estimates based entirely on PPM data.

Respondent PPM devices

Panelists in the survey carry small PPM devices that monitor the audio environment and identify PPM encoding if it is present. Arbitron says its devices can reliably detect PPM encoding after only a few seconds of exposure to the encoded stream, even in noisy acoustic environments.

Headphone listening is accommodated through the use of “loop-through” jacks; external source equipment (for example, a walkable radio) is connected to the PPM device with a short jumper, then the listener’s headphones are plugged in to the PPM device itself. The PPM devices have their own internal clocks and maintain a record of decoded audio streams throughout the day.

The PPM devices also contain sensitive motion sensors, and can add a notation to their internal logs when they are not moving. This notation can be used to exclude “listening” results that might have been recorded while a device was not actually being carried by its survey respondent.

Arbitron makes available dedicated rack-mounted decoder boxes that are programmed to respond to the presence or absence of a particular encoding stream. By connecting these decoders to an off-air feed, the broadcaster is warned when encoding has failed.

Arbitron equipment

The encoders and the confidence decoders are the only components of the PPM system whose operations are under the broadcaster’s control. While their deployment is relatively straightforward, the number of these boxes required to support the program streams generated by a cluster of stations can be surprisingly large.

(click thumbnail)Silence sensors and Arbitron confidence decodersStart by considering how many separate programs in your facility will require Arbitron encoding. Our facility, with one AM station and four FM stations, various HD-R and streaming offerings, and backup air chains for every program, required no less than 44 separate Arbitron encoders.

Even if your facility does not have dedicated backup air chains for every single program stream, it is nevertheless advisable to install backup Arbitron encoders for every stream. These units can be wired in series, with one unit actively encoding and the other unit in bypass.

With such a backup unit already installed in this “hot standby” configuration, a failure of the main encoding unit can be quickly remedied. Without a backup encoder, you would need to wait for a replacement unit from Arbitron. During that time your facility would not receive any PPM listening credit.

Next, consider how many confidence decoders will be required.

For most organizations, a reasonable guideline would be, “If it is important enough to encode in the first place, it is important enough to make sure it is being encoded.” In our case, we elected to obtain confidence decoders for all 22 of our program channels.

The confidence decoders have XLR audio inputs for connection to encoded audio (preferably, from an off-air or post-transmission source), and a D-connector that provides a dry contact closure indicating that encoding is successfully being detected.

The confidence decoders also come equipped with a rear-panel RS-232 output, which outputs a text stream at periodic intervals, indicating either that encoding is being detected, or that encoding is not being detected.

In the Philadelphia market, Arbitron’s engineers were in contact with market engineers commendably early in the PPM rollout process. We placed orders for encoders and decoders many months before the system was scheduled to go online, and equipment showed up in plenty of time for both main and backup units to be installed and thoroughly tested.

Verification of proper encoding in many cases could be done over the telephone. A local engineer could simply hold his telephone receiver up to a speaker playing various examples of encoded audio, one program at a time, and the Arbitron engineer at the other end of the line could verify the encoding was correct.

Other equipment

As if the prospect of the sudden delivery of 66 boxes of equipment isn’t daunting enough to you and to your receiving department, it is worthwhile to examine what other equipment will be needed to monitor your system successfully.

Recall that since Arbitron’s PPM encoding process analyzes the program and adds encoding energy where it won’t be audible, it follows that if for some reason a program stream is silent, PPM encoding cannot occur. The predictable result is that a station will not get ratings credit for any period that it has silence on the air.

Given this, evaluate all air chains to be certain they can successfully and automatically recover from silence problems. Many devices exist that can monitor a program air chain and switch to a backup source (an emergency CD, for example) when silence is detected.

Secondly, an off-air silence sense is a useful tool for technical responders to evaluate whether Arbitron decoder alarms are in fact due to an Arbitron encoding problem, or are simply due to silence on the air. This is especially important for channels that may not be easily monitored by an on-call technical responder, such as HD-R or Web streaming channels.

In our case, we elected to replace a haphazard existing system of silence monitoring with new, centrally located silence sense devices, one for each program stream.

Next, monitoring requirements should be addressed. Each Arbitron confidence decoder and the associated silence sense for that channel, if one is used, needs to have a dependable source of off-air or post-transmission audio.

Analog channels each require a dedicated analog tuner. HD1 and HD2 channels each require dedicated HD Radio tuners. Web streaming channels each require a dedicated computer or a dedicated Internet radio appliance “tuned” around the clock to recover audio from the stream in question.

Your facility should plan to acquire these monitoring sources, or if you already have them, plan to extend audio from the monitoring sources to the Arbitron confidence decoders and silence senses. Do not overlook that a stack of individual computers used to monitor your Web streams will probably require consumer-to-pro level audio interface converters, a local rackmountable pullout monitor and keyboard, and a large, remotely accessible KVM switch.

Last, all the dry alarm contact closures from Arbitron and from silence sense equipment need to be connected to remote control monitoring equipment. Such a remote control should be capable of permanently logging error conditions and then generating several types of alarms, from e-mails and pages to POTS line voice callouts.

It is also useful to consider a system that can evaluate alarms and make appropriate callout decisions. For example, problems with Arbitron encoding on a main analog channel are top priority and delivered to all on-call engineers, while problems with stream encoding are delivered to the IT department on-call staff.

You may need to find space for new racks, as well as evaluate power and cooling needs.

Other considerations

Give some thought to where in the program chain to locate the Arbitron encoders. Arbitron recommends that they be installed after a pre-limiter, but before final audio processing and before EAS encoding equipment.

Note that this means a station would not be generating Arbitron encoding while its EAS device is running tests, forwarding alerts, etc., assuming the EAS encoder is in the air chain and not an input to the console.

A station using a broadcast delay system should install the Arbitron encoder after the delay, so that an obscenity “dump” wouldn’t disturb the encoding.

Stations that don’t use an obscenity delay nor IBOC delay may question whether the Arbitron encoder adds enough throughput delay to cause problems with live off-air headphone monitoring.

Very early versions of Arbitron encoders were a concern in this regard; some air personalities were sensitive to the post-Arbitron encoded sound and found it somewhat unpleasant. However, our experience was that Arbitron worked attentively to address this issue, improved its coding algorithms very significantly, and effectively solved this problem in early field testing many years ago.


Installation of the Arbitron encoders is easy. XLR connectors are provided on the rear panel for audio in and out connections. The device is equipped with a hard relay bypass, so that if power is removed from the unit, a relay releases to directly connect the input to the output connectors.

A front-panel, key-operated switch provides a similar function; turning the key to the “Bypass” position also connects the input and output connectors. Software inside the unit will also force a bypass if certain error conditions are detected.

The unit has a front-panel LED that is green when all is normal and flashing red when various faults occur. The unit also has an LCD screen that provides messages about the current state of the device.

A vital step in the setup process is to verify with Arbitron that the encoders all work as intended. Consider that in a market-wide rollout, hundreds of boxes will need to be processed, shipped and installed; you would like to know for certain that the box in your station’s air chain that will be responsible for your station’s ratings is the correct one, and that it is working perfectly.

The confidence decoder installation is also straightforward. Plug line-level audio from the correct air monitor on XLR connectors into the box, and the front-panel LED will almost instantly change from flashing red to steady green.

A confidence decoder box will only successfully decode its dedicated companion encoder. For example, WJJZ’s decoder will not show a green light if it is hooked to WMMR’s off-air monitor, even if WMMR’s encoding is working properly. Arbitron says its decoders have an internal three-minute delay before a loss of detected encoding results in an alarm.


Greater Media elected to acquire additional space in our building’s penthouse mechanical area to hold the three new racks full of Arbitron confidence monitoring equipment we installed.

The leftmost rack contains the monitoring devices: analog tuners, HD-R tuners and rack-mounted CPUs for Web stream monitoring.

These are arranged in frequency order from top to bottom, with the analog tuners first, the HD-R tuners next, and the CPUs at the bottom.

Since monitoring devices for our entire facility are now centrally located, we also located a remote node from our routing switcher to this rack, bringing access to all of these feeds, many of which were never commonly available before, to all routing switcher destinations in our facility.

The middle rack contains half of the remote control system, all of the dedicated silence senses — one per monitored program stream — with each arranged to the immediate right of its corresponding audio source.

Finally, the rightmost rack contains the other half of the remote control system and the Arbitron confidence decoders. Again, each one is arranged to the right of its corresponding monitoring source.

Walking in to the room, it is easy to see at a glance the status of the various devices. Blank spaces were left in the rack at appropriate locations for the eventual installation of HD3 monitoring equipment.

The remote control system continuously monitors the various dry status contact closures of the system, and responds on an alarm condition. E-mails and pages are sent, and the system can place POTS calls and speak in English to an on-call respondent.

Possible improvements

We have added a remote power cycle feature to each of the tuners in the rack, such that if the remote control notices a silence sense indication of failure on a particular tuner, the remote control can issue a momentary pulse that will cycle the power for that tuner. If a receiver lock-up caused the silence problem, the reboot would cure the condition before the Arbitron confidence decoder’s three minute time-out, preventing nuisance alarms.

Keeping computers running and happily connected to a live Web stream is an ongoing issue. Nuisance alarms occur when a machine spontaneously disconnects from its host and comes up silent. We respond to these alarms by logging in via VNC from a remote location and manually restarting the affected computer.

Other audio monitoring points have been considered, such as the post-encoded audio right before it leaves our office on the way to the stream host provider. We rejected these alternatives because if used, they would be unable to alert us to problems that might develop with the streaming host itself.

We are experimenting with the use of the Roku SoundBridge M1001, a small, inexpensive device that can directly access Internet streams and which, in theory, would offer several advantages: The Roku doesn’t require a dedicated computer so it is much less expensive. The device can be easily remotely controlled and reset via Ethernet, and it will automatically and continuously try to reacquire the stream should the stream be temporarily lost.

The author gratefully acknowledges the use of information contained in Arbitron publications “Studio Grade Encoder: 1U Analog Interface. Operations and Field Service Manual” and “CBET Encoder Monitor. Operations and Field Service Manual.”

This article is based on his NAB Broadcast Engineering Conference paper, “Practical Considerations of Radio Broadcast Operations in an Arbitron PPM Market.”