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Artist Experience and Album Art Via HD Radio

The Clear Channel deployment experience

Fig. 1: OEM Automotive Radio: GMC Terrain

Fig. 2: OEM Automotive Radio: Toyota/Lexus The author is a senior operations engineer for Clear Channel Media + Entertainment’s Engineering and Systems Integration Group. He holds several SBE certifications including CSRE, CBNE, AMD and DRB. His opinions are not necessarily those of Clear Channel or Radio World.

In the United States, many broadcasters have employed HD Radio as a method to provide digital transmission alongside analog transmission on the FM and AM bands. While the initial focus of many broadcasters implementing HD Radio was to provide digital audio delivery to consumers, some of the emphasis on this has changed in recent years. The HD Radio transmission system is flexible enough to use portions of the digital spectrum for data instead of audio.

All of the emphasis for data delivery via HD Radio has been on the FM bands, as the data rate starts at 96 kilobits per second (kbps) in standard MP1 hybrid mode. The audio channels on HD Radio use adjustable-bitrate codecs, so the bitrate of the audio channel(s) can be reduced slightly to allow for additional data services. The total available bandwidth increases from 96 kbps to 124 kbps in MP3 mode, 149 kbps in extended hybrid MP11 mode, and 253 kbps in all digital MP6 + MS4 mode.

At this time, the AM HD Radio system does not offer the framework to provide these services, as all the data must be used for the audio codec. There is also considerably less bandwidth to allocate for this process, which would decrease audio quality. MA1 Core Only mode offers 20 kbps, MA1 Full Hybrid mode offers almost 37 kbps, and MA3 All Digital mode offers nearly 40 kbps.

Data services delivered over HD Radio are an exciting and growing development in the industry. One of the most visible applications of data delivery is the concept of using some of the data bandwidth available in the HD Radio stream to deliver graphical images synchronized with the audio. This involves sending images related to the current song on the air, such as album cover art. The concept is known as Artist Experience. The concept dates back to the earliest inception of Advanced Application Services over HD Radio technology (1999).

Clear Channel Media and Entertainment worked with iBiquity on the initial commercial efforts of this service and started the first implementations of Artist Experience in June 2010. The two companies worked together to provide a proof of concept and an initial development of this new feature. The result of that effort included an implementation offered by iBiquity to all broadcasters, which became available in May 2011.

Fig. 3: OEM Automotive Radio: Volkswagen

Fig. 4: Aftermarket JVC (upper) and Kenwood (lower) Because Artist Experience was evolving, Clear Channel’s initial rollout took some time and was only offered on a limited number of stations so that development could be focused. Much planning was needed to develop an internal solution for providing album art to many stations concurrently. The design needed to consider approximately 390 HD Radio stations running Artist Experience, which when coupled with HD2 formats meant that the system had to simultaneously support approximately 780 individual audio channels. It also needed to be scalable for any additional stations we decide to convert to HD Radio in the future. To date, there are no products on the market that scale to this level.

Clear Channel completed its nationwide rollout of Artist Experience in September 2012. This process has not gone without challenges. We have learned quite a bit in the process and continue to refine our implementation. It is our hope to share this information with the industry to help assist other broadcasters and vendors in this endeavor, as we feel this is a good development for the industry.

Receivers with Artist Experience support are being released to the marketplace in various forms, including but not limited to portable, tabletop, aftermarket automotive and OEM automotive (factory-installed car radios). A list of some of the products available for purchase that support this technology are in Table 1, and some Artist Experience images from these receivers are shown in Figs. 1–5.

The number of receivers supporting Artist Experience continues to grow, and there is interest from automotive manufacturers in implementing this feature. BMW, Buick, Chevrolet, GMC, Lexus, Mazda, Toyota and Volkswagen have radios in some of their models that support it. More designs from these manufacturers and others are on their way.

There are multiple factors driving this. Consumers are used to smartphone devices with interactivity and apps — and the automotive space is starting to embrace this trend. In addition, the United States Department of Transportation is mandating backup cameras in all vehicles produced after May 1, 2018. Most implementations require an LCD screen in the “center stack” of the dashboard — where the radio typically is. Automotive companies are looking to use this screen in ways to produce a positive experience for the driver and passengers when the car is not in reverse. Artist Experience is one of the items many automotive manufacturers are implementing — it is free content for them — and this is certainly an exciting feature that radio stations can offer to their listeners.

Artist Experience offers a great listener benefit. It also gives terrestrial radio a visual element to help compete with so many other digital audio products, such as portable audio players, streaming websites and smartphone apps.

The image displayed must be tightly synchronized with the song or audio being played. Only one image can be associated with an individual song. If the Cover Art or primary image is unavailable, a station logo or other default image is displayed on the receiver. Fig. 5 shows an example of a station logo.

Fig 5: Insignia Tabletop and Portable Program Service Data (PSD), formerly known as Program-Associated Data (PAD), is a structured data format that provides metadata (title, artist, album and other information about the song) currently on the air. PSD messages must arrive at the broadcast equipment within 0.5s of each new segment or song, so that the image can be tightly synchronized with the song.

The image synchronization trigger is sent through a custom frame in PSD called the XHDR. The image should be sent prior to the start of the associated song. Transmitting station logos is critical since receivers use the logos as a fallback when song specific synchronized images are unavailable.

The emphasis in this paper is to help broadcasters implement Artist Experience on their stations. To do that, one needs to understand the overall system architecture and the requirements in greater detail.

First, the station must be an FM station transmitting an HD Radio signal. That is an entire topic in itself, but it requires a transmitter and exciter capable of generating the digital IBOC waveforms. The exciter has an Exgine card, which is an Ethernet interface that accepts HD Radio encoded information from the Exporter. This link is considered the Exporter to Exciter (E2X) link. The Exporter should be running IRSS 4.3.2 or greater. Clear Channel recommends and uses version 4.4.7 on all of its stations, which is the latest available at the time of this writing. Exporters running versions below 4.3.2 will need to be upgraded; consult your equipment manufacturer for assistance.

If you are planning an upgrade, be sure to use 4.4.7. While 4.4.7 is not required to deploy Artist Experience, it adds a few new features. And most important, it adds to the robustness and stability of your HD Radio systems. Note, Exporter and Exciter hardware combinations that predate the Exgine configuration platform use Low Voltage Differential Signaling (LVDS). These systems can also support Artist Experience if using the proper software versions.

The Exporter encodes the Main Program Service (MPS) HD1 audio, along with any data that comes from an Importer. Typically, the Importer was just used for encoding your Secondary Program Service 1 (SPS1) HD2, SPS2/HD3, etc. audio channels. However, it is also where any ancillary data sent via your HD Radio signal is put together and transmitted to the Exporter. This data is aggregated by the Importer and then transmitted through the Importer to Exporter (I2E) link. Since Artist Experience is an additional data stream, it is encoded on the Importer as well.

The Importer, too, should be running version 4.4.7. While 4.3.1P1 may work, we strongly recommend 4.4.7 in combination with Exporter 4.4.7. This pairing makes the I2E link very robust. It also includes a newer version of the SPS Capture Client which encodes the SPS (HD2, HD3, etc.) audio that is much more robust and stable than previous versions. The Importer must be configured to allocate a portion of the HD Radio data bandwidth for Artist Experience. This is typically 4 kilobytes per second.

Many engineers and IT technicians who have implemented HD Radio systems before are familiar with these components we have just discussed. The biggest change — and how Artist Experience is implemented — is a program called MSAC that runs on the Importer.

MSAC is a platform-independent software program written in Java and designed by iBiquity, used to send data over the HD Radio transmission system. It can be configured in a variety of ways depending on the data transmission requirements. In the case of album art, it is used in a Large Object Transfer (LOT) capacity to transmit images at specific times to receivers.

The MSAC client software is distributed by the Importer manufacturer and the license is conveyed as part of the Importer license. Station usage of MSAC falls under the standard terms of the advanced services license with iBiquity.

MSAC accepts incoming TCP or UDP messages from a data provider. For Artist Experience, TCP/UDP messages must be sent from the server, application or device that is providing your album art. This information is transmitted to MSAC via a structured data format provided by iBiquity when a developer makes arrangements to obtain the MSAC API/SDK. Once received, the images are scheduled to be transferred via the HD Radio transmission system.

In the case of Artist Experience, there are two types of requests that are sent to MSAC, pre-sync and sync events. And for station logo, there are async events. These events associate images for transmission via the HD Radio data system.

For the image to be shown successfully at the start of the song, the image must be transferred to the receiver before the song occurs. That is because there are inherent delays in the HD Radio transmission system as information is buffered, transmitted and decoded. In addition to those encoding delays, there are transmission delays in the album art data channel itself.

Album art images are in the JPG or PNG format, sized to 200 x 200 pixels, and have a maximum file size of 24 kilobytes. Generally, the data size allocated for transmission of Artist Experience is 4 kbps. So, a maximum file size image of 24 kilobytes would take 48 seconds to transmit. Smaller files obviously would take less time to transmit.

Fig. 6: Clear Channel Artist Experience System Topology
The Artist Experience bandwidth is pooled across all HD channels, so the images for the MPS/HD1, SPS1/HD2 and other channels share the same data bandwidth. Since it takes time to transmit files through the data channel, there is possible contention between multiple HD audio channels (two songs may start at approximately the same time).

MSAC must schedule sending the image before the song starts depending on the bandwidth allocated, the size of the image and considering when images may need to be transmitted for other audio channels. MSAC is dynamic and does these calculations on the fly. It is configurable and will optimize to make use of the available bandwidth based on the following factors: size of the image, the image repeat rate and the image data transfer rate.

The key to making sure those images arrive at the radio before the song starts is to have MSAC properly configured, have your time synced to a reliable source for all systems (automation, any middleware, Importer) and have your systems accurately predict when the next song is going to play. Timing is very important, and if the system time of any of these components departs from exact time, this could cause issues in transmitting images. It is important for solutions to consider any non-HD related delays in the transmission system in its timing calculations. Most commonly, this would be the use of profanity delays on the radio station. Commands being sent to the MSAC must be compensated for any non-HD related delays, such as a profanity delay.

Table 1. Select Receivers With Artist Experience The best way to make sure images are sent at the proper time is to ensure the on-air playback automation system is set to export the current song playing plus at least one (or more) of the songs next to play to your album art services. These systems can then forward the estimated time the next song will play to MSAC. When MSAC has this information, it can make sure images are delivered once to receivers shortly before each song starts.

Typically, if the timing calculations are correct from the automation feeds the item will be received by a receiver about 10 seconds before the song starts. The receiver stores the image and prepares it for display.

When the song starts to play, your Artist Experience solution needs to do two things concurrently.

First, a Program Service Data (PSD) message needs to be sent to the Exporter (MPS/HD1) or Importer SPS Capture Client (SPS1/HD2, SPS2/HD3, etc.). This is likely already happening in your older system so that radios could show the PSD (title, artist, album etc.) of the current song in text form on the receiver display.

However, to implement Artist Experience, your systems must incorporate HD Radio HDP PSD SDK v4.7 or greater. These versions support an image synchronization trigger through a custom frame in the PSD called the XHDR. This trigger matches an image previously sent by MSAC through a unique identifier called a LOT ID. Without the PSD message with the XHDR trigger, the image would simply sit in the receiver memory but never be displayed. The PSD trigger is what indicates to the receiver that the image is associated with this song. As mentioned previously, the PSD message timing must also be compensate for any non-HD transmission delays, such as a profanity delay, to make sure the PSD (title/artist) data and the image are displayed when the song starts and stops.

The second item that needs to happen concurrently with a new song starting is that your systems need to send a SYNC event to MSAC to let it know that the song has started playing. This allows MSAC to schedule a send of the image shortly after the song start. For receivers that were tuned in before the song started, this is a redundant send and ignored. For those receivers that were not tuned into the station before, or had a data impairment issue at time of transmission, they will receive the image shortly after the song starts. Remember, the sync event should also compensate for profanity or other delays.

The SYNC event also allows MSAC to know if the timing of the song start has changed. This could happen if the song was started early for some reason, i.e. maybe the on-air operator started it earlier than scheduled, or quickly juggled around the schedule. The SYNC event keeps MSAC up-to-date with the song timing information so that it can continue to optimize the transmission of images to receivers. Depending on the configuration of the MSAC, it is possible for MSAC to send the image a third or more times after the song has started. However to conserve bandwidth, it is typically recommended to only send it once more, perhaps no later than halfway through the song.

To transmit a station logo, there are a few things to consider. The logo image must follow the same technical specifications (JPEG or PNG, 200×200, under 24 kilobytes). MSAC must be told about the station logo via a slightly different message called an ASYNC SEND request. This request needs to be sent periodically so that MSAC is aware of the logo associated with the specific channel (HD1/MPS, HD2/SPS1, HD3/SPS2, etc.). Once the request has been received by MSAC, it will schedule the station logo to be sent periodically. While configurable, Station Logo tends to be broadcast once every 15 minutes or less. MSAC treats this as a low-priority send.

When MSAC sends the station logo, receivers that support this service will cache the logo. It can be displayed in instances where no Artist Experience image was sent for a particular song. It can also be displayed when the broadcaster sends a specially crafted PSD XHDR message to the receiver indicating that the station logo should be displayed. For instance, at Clear Channel, we use this command when we display the default generic PSD messages, so that receivers that support Station Logo will display the image.

It should be noted that not all radios that support Artist Experience support Station Logo. While Station Logo is supported in the majority of receivers, the decision to implement this feature is left with the receiver manufacturer. They may leave it out to control cost or conserve available memory space. On these types of radios, they may display a generic image for all stations, such as the HD Radio logo, or perhaps a generic music note or other image.

An item left to the receiver manufacturer is how to store or cache images. Some advanced designs cache these images to non-volatile storage devices such as flash memory or a hard drive. These tend to be some of the best implementations, because the radio will associate and store the image for a particular station, song, title, artist and its unique LOT ID. For these receivers, you can tune into the station and receive an image once and the radio will remember that image for that song. If you tune away to another station and then tune back to the original station, the image will display immediately. Or, you could tune into that station hours or days later and in the middle of the song and the receiver can display the image immediately.

In contrast, other receivers only store the images in volatile memory, which means that it only stores the images temporarily. There are some that save them per radio listening session, so they will act like the radios with more permanent storage methods, but when the receiver is powered off, it loses these images.

Others at lower price points limit memory, as it is a considerable cost factor. There may only be enough memory to store the image for the current song and the next song. If you tune away from a station in the middle of the song, and then tune back, it may purge the images in memory. Then you will have to wait until MSAC transmits the image again before it will display to the consumer.

These same storage and memory considerations apply to the Station Logo service as well. You may notice certain receivers permanently storing station logo images, while others might need to wait until that is sent over the HD Radio system by MSAC before displaying it each time you tune to the station.

Another consideration in implementing Artist Experience is licensing the use of album cover art or other images for transmission. Clear Channel directly negotiates with providers of these images for our many distribution platforms (iHeartRadio streaming, web/digital, mobile, etc.) so we were able to include HD Radio as part of our licensing agreements.

One of the largest challenges in this process has been trying to include relevant artwork for all of the songs that our stations play across the country. Clear Channel employs a centralized database of all songs, which is managed and maintained uniformly throughout the enterprise. This offers us great benefits, in that everything related to the songs we play can be managed, including extended song metadata from a single source. Clear Channel catalogs more than just artist and title, but many other relevant fields, such as iTunes reference data and album art image data. We are constantly striving to improve the match rate of songs and album art. However, it is a continual process to maintain that library.

Much of this paper has focused on the early development and concepts behind Artist Experience from Clear Channel’s implementation perspective. These components are summarized in Fig. 6. While the scale of the system we have developed is extensive, such scope is not necessarily needed for individual stations or small- to medium-sized group owners to employ Artist Experience on their stations.

There are several third-party software/hardware companies that provide solutions. While neither I nor Clear Channel endorses any particular vendor named below, these companies have partnerships with iBiquity and automation system vendors to provide Artist Experience for your stations.

Regardless of which solution you select, the concepts mentioned above apply to whether your company develops its own Artist Experience system like Clear Channel did, or decides to select an outside product. The providers below offer middleware software/hardware solutions that can be placed between your on-air playback automation system, and the HD Radio software/hardware infrastructure designed by iBiquity.

These solutions collect the now playing and future playing song information from the station’s on-air playback automation systems, match them with album art or other relevant images, and send them to the Importer and MSAC for transmission.

Each of these vendors offers matching of songs to cover art, and can assist you in matching, monitoring, maintaining and licensing those images for transmission:

Arctic Palm’s Center Stage

Broadcast Electronics /
“The Radio Experience” (TRE)

Emmis Interactive / TagStation


Standardization is the main reason why Clear Channel was able to implement this feature so rapidly nationwide. Once the final parameters of deploying Artist Experience were determined, we were able to convert the initial batch of approximately 80 stations in a matter of weeks to our new systems. We learned from that process, and used those experiences to help roll out the remaining 310 stations in a period of three months. The final push of 170 stations was completed in a two-week timeframe. Our standardization process was so refined that an individual engineer at the market level would spend approximately an hour onboarding their first station, and then typically 30 minutes or less implementing additional stations.

For those charged with implementing Artist Experience on more than a handful of stations, I strongly recommend that standardization be considered as part of your Artist Experience deployment strategy. There are many components needed to execute this properly and it is best to consider standardizing to implement this rapidly.

I recommend that you standardize your Exporter version to version 4.4.7. Make sure every station is running the same version of Exporter. Having a variety of versions may cause you slight variations or differences in your rollout.

Similarly, I recommend that you standardize your Importer version and configuration to version 4.4.7. Much of the legwork to get Artist Experience working involves configuring the Importer. It seems many engineers deal with importers on a one-by-one basis. If you have only a few stations, that might be fine. But upgrading importers, reinstalling software and other aspects can be cumbersome and not easily duplicated amongst several Importers. If you have more than a few stations, you should consider putting your IT skills to work and develop a standardized image (OS included) for the Importer. Hopefully you do not have too many hardware variations to consider as part of this. It does help in cases where you have a large variety of types of Importer hardware to consider standardizing on a single hardware platform. That makes this process much simpler to implement. Also in cases of a hardware failure, it is much easier to restore the station back to full functionality. If you do go in this direction, start with a freshly formatted hard drive, a new OS installation, new installation of Importer 4.4.7 and latest MSAC. Have all of your configurations complete before creating your system image.

If making images of the entire Importer is not something you wish to do, I do encourage making backups of the Importer and MSAC configurations from an Importer where you have everything working to your satisfaction. You can restore these configurations on other Importers, but you will also have to closely monitor version differences on the Importer software and MSAC. The amount of time you spend upgrading Importer versions and restoring configurations can be extensive. This is why I recommend developing a full image for the Importer already installed and configured the way you want it.

While I cannot offer advice of which vendor to select, I recommend you work with one you have experience with, ask colleagues what solutions they have used and consider evaluating several products. Once you’ve made a selection, standardize on this solution for all of your stations.

Get a few stations working with standardization in mind, and learn from those implementations. This will make your deployment go so much faster and save you considerable time, resources, and frustration.

Make sure you invest in a receiver that supports album art. At this point, I would recommend using one of the aftermarket automotive radios. Personally, I have used the JVC devices the most, and their Album Art implementations are very good. While they are expensive, you can either install them in a car as designed or in a fixed location with a good antenna. The portable units on the market are not as sensitive or robust. I would not encourage you to make decisions on timing, delays, and derive an overall impression of Artist Experience from these devices. Hopefully that experience will improve in the near future.

Special thanks to Jeff Detweiler and colleagues at iBiquity Digital Corp. for providing additional details on Artist Experience to help further the education and understanding of this technology.

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