If you are a frequent reader of Radio World, you may have seen articles from myself and others discussing HD Radio time alignment over the last few years.
At the Radio Show in September, the NRSC adopted NRSC-G203 IBOC Time and Level Alignment Guideline, which can be found here: http://tinyurl.com/yc8u8dxw.
Perhaps at first glance, it might appear to be more of the same — but this is a new document that goes beyond the research and experience of just one person or company’s experience or viewpoint. The majority of the content in this document was researched and developed by the NAB Radio Technology Committee. The draft NAB document was submitted to the NRSC in April for final review and released as an NRSC guideline.
NRSC-G203 is the first comprehensive, collaborative effort of the industry to consolidate all of what is known regarding this important topic that directly impacts the listening experience.
WHY DOES IT MATTER?
If your station(s) employs HD Radio, depending on the population you serve, you likely have hundreds, if not thousands, of listeners listening to your station in HD, and they don’t even know it.
While the radio industry has frequently griped in the past about the lack of HD receivers and raised eyebrows about the number of HD listeners that are actually out there, the reality is, they are out there, and the number of listeners to your HD signal is growing at a rapid pace.
While broadcasters have recently been more focused on other areas (streaming, websites and social media), HD Radio receiver quantities have been growing by the millions each quarter, thanks to increasing adoption of HD Radio by automotive manufacturers in many popular makes and models. HD Radio is showing up as standard equipment at all automotive price points.
|Xperi New Vehicle OEM Penetration Report Mid 2017
(Click to Enlarge.)
The latest numbers provided by HD Radio technology owner Xperi indicate that in the first half of 2017, nearly 46 percent of all new automobiles included HD Radio. For those following the last few years, there has been an increase each year. HD Radio receivers are being deployed at an accelerated pace, and we’re now seeing a critical mass of HD Radios out there, in markets large and small.
Total U.S. HD Radio penetration is now at 14.4 percent of all cars on the road, but Xperi also maintains market-specific research data. There are nine markets that exceed 20 percent now, and two of those are over 25 percent. Imagine that — one in every four vehicles in the New York and Miami markets have an HD Radio. And in many other markets one in every five vehicles has an HD Radio.
What’s also interesting to note is this trend is happening in markets with large populations and small populations. In New York, there are over 3 million HD Radios in the market, and Los Angeles has almost that many as well. It’s an important trend that this industry needs to start focusing on.
While you might not have an HD Radio in your car, many of your listeners do. Imagine: 20–25 percent of your mobile audience is listening on an HD Radio. We can no longer ignore this audience.
Remember, if your station’s analog and digital signals are not precisely time aligned, this will cause the “blend” between the two to become audible, and the further out of specification, the worse the experience can become.
The blend happens more than once for most listeners. For listeners at the edge of coverage, their radio may be crossing between analog and digital constantly, and if your time alignment is not perfect, and if your audio processing is not nearly identical on the two channels, it can cause your station to sound awful.
As we’ve noted in previous articles, some stations are misconfigured so that the amount of delay is drifting constantly. The end result is the listener hears this and, not knowing that it is the radio station that is the problem, often complains to the automotive manufacturer or their car dealer about the radio receiver having a problem.
|Xperi Top 10 HD Radio Penetration Numbers. *HDEC=HD Radio-Equipped Cars
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This is the number one complaint automotive manufacturers have about HD Radio — that the broadcasters are offering a poor listening experience.
It is very important that the radio industry focuses on the listening experience of this growing audience. The automotive industry has finally embraced the technology our industry deployed over a decade ago. It’s time for broadcasters to start paying attention to these systems and the listening experience.
WHAT DOES NRSC-G203 BRING TO THE TABLE?
This document was the result of a collaborative effort of dozens of engineers, from a wide variety of backgrounds, all of whom have unique experiences with HD Radio transmission. This group included station-/market-level and corporate engineering personnel from many different broadcasters, large and small across the country.
In addition to this, all the major vendors that produce transmission hardware, as well as time alignment measurement and correction devices, provided feedback.
Design and implementation engineers at Xperi (formerly DTS, iBiquity, the creators of HD Radio) also were involved, commenting and contributing.
While previous papers and articles on this topic have discussed various aspects of this, NRSC-G203 brings the collective knowledge of the industry into a single reference document. Instead of casually discussing certain parts of the system, this guideline discusses and diagrams all major implementation methods used by broadcasters.
Much care was taken to create system diagrams of all known implementation methods. These methods were discussed, and then companion diagrams were developed to show where automatic time alignment would be inserted into the air chain to dynamically correct for the problem.
This document discusses many different issues that have been known to cause drift or time shifts and alignment problems. It discusses best practices on how prevent them from happening.
EXPORTER AT THE STUDIO NOT RECOMMENDED WITHOUT AUTOMATIC TIME ALIGNMENT
In what was perhaps a breakthrough for the industry, all of the collaborators discussed and agreed that today’s current transmission hardware, the commonly deployed third-generation Exgine system, is not able to maintain precise time alignment manually when the exporter is not collocated with the exciter.
While I have mentioned this in the past, it’s important to note; there were no objections to this premise amongst all the parties.
Simply put, if your exporter is not at the same site as the exciter (i.e. exporter is at the transmitter site) then the industry has agreed that some form of automatic time alignment/correction is required to meet the NRSC-5 time alignment specification. The best practice would be to collocate the exporter to the same location as the exciter.
But the NRSC recognized that some broadcasters would be reluctant to do that, based on costs, operational convenience or other factors. After much discussion and research, it was agreed that it could be possible to maintain specification, but it requires continuous, active time alignment methods to be implemented.
|This image, Fig. 19 in the NRSC document, shows exporter and audio processor located at studio, Exgine located at transmitter utilizing inline auto correction.
(Click to Enlarge.)
Depending on your station’s STL configuration, if you do have the exporter at the studio, the cost to upgrade the STL to a bidirectional link might be greater than employing some of the automatic alignment devices or systems.
For example, see Fig. 10 on page 21 of the NRSC document. This is a pretty common deployment of HD Radio, with the exporter at the studio. The NRSC specifically does not recommend this, and suggests co-locating the exporter at the transmitter site as the best option, or if that is not possible, using automated alignment as shown in Fig. 19 on page 33 of the document.
EXPORTER AT THE TRANSMITTER SITE
Even though the exporter at the transmitter site, collocated with the exciter is the preferred installation method, that does not necessarily mean you do not need to have automatic time alignment, either.
NRSC-G203 goes into great detail on what external factors can cause drift or jumps in time alignment in this environment, as well. The problem is, without the latest time alignment measurement hardware out there today, you likely have no precise way of knowing you are in specification either.
Just because the exporter is collocated with the exciter does not mean you are immune from this problem. There are still a variety of best practices discussed in detail (i.e. E2X network isolation, direct 10 MHz/1 pps clocking configuration, GPS synchronization, ensuring the exporter and exciter are on a UPS, etc.) in the document.
SEPARATE PROCESSORS NOT RECOMMENDED
The entire industry has come behind the recently learned guidance that separate processors are not good for blending, even when the station has perfect time alignment. The NRSC encourages common, single-box, integrated FM+HD audio processors.
Note that if your exporter is at the studio, while an inline correction device can fix the drift caused between the exporter and exciter not being collocated, it cannot fix the problems caused by separate, dissimilar processors, which are often deployed in these split systems. Hence, the best solution is to collocate everything at the transmitter site, and employ a single FM+HD processor.
LOW-COST MEASUREMENT TECHNIQUE
While there are new products that can measure and/or maintain the time alignment, they may not be initially available to you for various reasons.
While the industry struggled with getting time alignment right through manual means in headphones or using first-generation time alignment devices, we overlooked the common oscilloscope sitting in most radio engineering shops across the country. This, combined with an HD Radio in split analog/digital mode, can display a Lissajous pattern. This becomes a highly accurate time alignment/measurement device that is far more accurate than the primitive tools we used over a decade ago. See Section 5.2 for information on how to make these measurements. The desired result is shown in Fig. 14 on page 27 of the document.
KNOWN STABLE VERSIONS
For those who remember the early days of HD Radio, there have been many software and firmware updates over the years. One of the most commonly overlooked elements is that you might be running a known time-stable version on one station, but you might be running an older, non-time stable version of software on another station. Unless you dig into the configuration menus, you might not remember that.
You should review each station that you have and confirm it is on the latest software, as shown in Table 2 on page 24 of the document.
MANUFACTURER-SPECIFIC CONFIGURATION INSTRUCTIONS FOR DIRECT CLOCKING
Since the document strongly recommends to collocate the exporter and the exciter, Annex 1 (page A1-1, PDF, page 40) offers manufacturer-specific settings on how to do exactly that. Configuration instructions are included for most exciter platforms. In addition, verification instructions on how to confirm that the exciter is using that 10 MHz and or 1 pps clocking reference are shown.
I personally consider the information in this section to be more clear and concise than the technical manuals for these products. Perhaps over time, manufacturers can offer this level of information in their manuals and bulletins. But for those engineers with multiple types of exciters under their supervision, this is a one-stop reference.
Information on HD Radio time alignment has never been in one place.
This is a single, comprehensive document that has been vetted by the industry. It contains the best practices, everything the industry collectively knows on the topic. It allows engineers in the field to review the best practices, review how their station is currently configured — it suggests different topologies, and it also shows engineers where automatic corrective devices could be placed in their air chain.
The NRSC “G” series of guideline documents have been very good “how to” and “hands on” resources for the industry. This new G203 document adds to that collection.
Many NRSC guideline documents are revised periodically, and as the industry learns more on this topic, we can look forward to updated versions. If there are new techniques or configurations that evolve over time, this document can be updated to reflect that.
If you have a comment or contribution, the NRSC is looking for more participants, as always. We encourage interested parties to join and participate. But even if you are not a member, you can submit additional suggestions and feedback by submitting the document improvement form at the end of the guide.
Alan Jurison is a senior operations engineer for iHeartMedia’s Engineering and Systems Integration Group. He was a major contributor to the NRSC-G203 document and chairs the NRSC RDS Usage Working Group. He holds several SBE certifications including CPBE, CBNE, AMD and DRB. His opinions are not necessarily those of iHeartMedia, the NRSC or Radio World.