Digital Audio Broadcasting Survey results

I have been looking over this data for a few weeks and there are some interesting data points. First, I would like to thank everyone who participated. This is not a scientific poll, but rather an informal survey of those who chose to participate.

The survey consisted of ten questions and was posted on Facebook, Reddit as well as Radio World. There were 114 responses, which is a relatively small sample size and is less than anticipated. There were 5 people who opened the survey and then did not take it. This may indicate a level of apathy towards the subject. Most responses were from the United States, but there were a few from China, Europe, and Brazil. The average time to complete the survey was 1 minute 40 seconds.

The first question was a warm-up question and it shows a lukewarm response at best with the top two responses being “It’s Okay,” or “I am indifferent.”

A vast majority of respondents feel that testing other Digital Audio Broadcasting systems such as DRM30, DRM+, or DAB+ would be a good idea. In MB docket 19-311, the FCC left the door open for such testing in the future, stating in paragraph 26 “Finally, we (the FCC) emphasize that by approving use of HD Radio technology, we do not foreclose the possibility of authorizing alternative technologies in the future, if they are properly before us.”

Question #2 was an attempt to find out where most people are listing to HD Radio and radio in general. Not a great surprise that it is mostly in-car listening. The in-home listening is a little bit surprising. What is even more surprising is that 30% of the respondents do not have an HD Radio. HD Radio has been the digital audio broadcasting standard in the US since October 2002, when the FCC first authorized its use. Receivers are still an issue some 20 years into the project. I know that when I purchased a new vehicle (Ford) in April of this year, HD Radio was not an option in any but the highest trim packages. My first HD Radio receiver was a tabletop Sony XDR-S3HD purchased in 2006 or so for $200.00 which was a lot of money. A quick look on Amazon shows that the least expensive HD Radio is the Sangean HDR-14 for $70.00.

Questions #3 and #4 deal with the “analog sunset,” as originally proposed by iBiquity, the developer of HD Radio technology. After a period of time, according to the original plan, stations would turn off their analog signals in favor of all digital transmissions. In October of 2020, MB Docket 19-311 the FCC has allowed AM stations the option to do just that. Thus far, four AM stations have transitioned to all-digital broadcasting, one of which is off the air since the owner passed away.

According to the survey respondents, by a slim margin of 53-47%, all-digital AM is supported. The FCC has yet to consider all digital FM and by an equally slim margin of 46-54%, all digital FM is not supported.

Question #7 asks about perceived audio quality. I received a few email comments about this question. Three respondents noted worse audio quality on HD-2, HD-3, or HD-4 channels due to reduced bit rate CODECS. Five people skipped this question.

This gets to the crux of the problem; for radio station owners, it is expensive to purchase and install HD Radio equipment. If there are no great perceived improvements, what is the point? I find AAC audio codecs to be okay, however, there is a noticeable difference between CD player PCM and streamed audio no matter what the source. Low-bit rate codecs sound like they are coming from underwater. Why do we listen to the radio? Information and entertainment. I posted something many years ago: Listening to the Radio is like doing Cocaine. For the maximum dopamine effect, I like my music to sound like music, not some watery approximation.

Question #8 asks about additional features, most people find Program Associated Data (PAD) useful. Even in non-digital FM stations, RDS is an important feature and stations will get phone calls if the RDS is missing or stuck on one song for a prolonged time. Listeners have become used to glancing at the radio to answer that age-old question; what’s the title of this song?

In response to question #9 (How many hours per week do you listen to the radio (including streaming terrestrial broadcast radio stations via a website or smart device)? The average was 19.6 hours with a minimum of half an hour and a maximum of 90 hours. Interestingly, there were four people who put in 0 weekly listening hours.

Question #10 is very interesting. In spite of the lukewarm feelings it seems that most respondents would favor the FCC mandating a transition to all digital audio broadcasting by a margin of 62% with most opting for “at some point in the future.”

HD Radio has been stalled for some time. The technology has not lived up to the hype and for most stations, it is a way to feed an analog translator with additional programming. There is an overall lack of interest, the majority of those who did take the survey stated HD Radio was “okay.” Receivers are expensive and still difficult to obtain. All digital AM (HDMA3) has not progressed very far since the FCC allowed its use. Yet, the people who did respond felt that additional testing of various Digital Audio Broadcasting systems should be allowed. I don’t know, that ship may have already sailed.

AM radio in Electric Vehicles

I have been reading with interest the ongoing discussion about AM radios in Electric Vehicles. Rather than rehash the what, I thought it would be nice to dig into why it is happening.

My first thought is that many of the electronics use PDM or PWM to control various stages of charging, converting, or discharging the storage system. I quick review of a typical EV basic diagram shows that there are several systems involved

Searching through various chip makers’ data sheets on Li-ion battery chargers, DC voltage to voltage converters, regenerative braking systems, traction motor inverters, and so on shows that all of those systems use PWM. Some of those PWM frequencies are right in the AM band, while others are not. That explains why different manufacturers have different takes on AM radios in EVs.

Basic Electric Vehicle

All of those electrical components are controlled by an electronic system that handles battery charging,

This basic diagram shows several sections that rely on PWM to function. The traction inverter is very complicated, with sensors running to each motor and each wheel for traction control, etc.

I imagine the average EV driving down the road in a cloud of PWM-based electrical noise. Whether or not that creates interference with AM reception depends solely on the PWM frequency the chip manufacturer chooses. That is not all, even when sitting in the garage charging, the Li-ion battery chargers use PWM.

It seems a monumental task to attempt to mitigate the noise issue. The real question is; does the general public and more specifically, those who want to own an EV care about AM broadcasting?

There are many alternative entertainment options these days. I would say the average Tesla driver listens to iTunes.

It would be interesting to test MA-3 reception in a Tesla. That would be a real-world test to see how the HD Radio codec stands up to electrical noise. I would say the same about DRM, but you would need to find a receiver first.

All digital Medium Wave transmission

With the approval from the FCC for all digital broadcasting on the Standard Broadcast (AKA AM, Medium Wave, Medium Frequency) band, it might be interesting to dissect Xperi’s HD Radio MA3 (HDMA3) standard a little bit. It might also be interesting to compare that to DRM30 which has been in use in many other places around the world for several years now.

First, I will dispense with the givens; HD Radio sounds better than its analog counterpart. I have also listened to DRM via HF, and that too sounds better than its analog counterpart. Of interest here is whether or not either digital modulation scheme improve reception reliability and coverage area. Medium Wave has a distinct difference from other frequency bands as it can cover vast areas. Something that has been dismissed in recent years as unneeded due to reduced maintenance schedules and the cost of keeping directional antenna systems in tolerance (thus increasing skywave interference).

Secondly; after reading several studies of HDMA3 and DRM30, I will concede that both systems perform betterAnnex E, Ref 2; Section III para C, Ref 6 than their analog counterparts in a mixed digital analog RF environment. Both systems have features which can be used to improve reception during night time operation. Skywave exists, whether or not people want it. If it is not desired as a reception mode, it still has to be dealt with from an interference perspective.

The two main complaints against Medium Wave broadcasting is perceived reduced audio quality (over FM) and interference. The interference comes in two flavors; electrical impulse noise and broadcast (co-channel and adjacent channel AM stations). Both are problematic. To some extent; both can be somewhat mitigated by an all digital transmission. However, if the interference noise becomes too high, the program will simply stop as the data loss becomes too great to reconstruct the audio program.

Of further interest here is the technical aspects of both systems and whether or not one would be superior to the other for Medium Wave broadcasting. I found this comment on a previous post to be particularly interesting:

DRM and HD both use OFDM, but the parameters are quite different, eg. the length of cyclic prefix which determines the performance in sky/ground wave interference are different by a factor of 9 (0.3ms vs 2.66ms). That is why DRM is much robust than HD.

https://www.engineeringradio.us/blog/2020/04/all-digital-am/

First of all, is this a true statement? Secondly, does the cyclic prefix make a difference in sky wave to ground wave interference? Which system might work better in a broadcast service where there are 4560 stations transmitting (as of 9/2020) and creating interference to each other? Finally, could the implementation of either system make a worth while difference in the quality and reliability of Medium Wave broadcasting in the US?

To answer these questions, I decided to begin with the technical descriptions found in the definitive documents; NRSC-5 D 1021s Rev GRef 1 for HDMA3 and ETSI ES 201 980 V4.1.1Ref 2 for DRM30.

There are many similarities between the two systems; both use COFDM modulation schemes, both have various bandwidth and data rates available, both use audio codecs that similar, both have some type of FEC (Forward Error Correction) system. I prepared a chart of these characteristics:

Feature/SpecHDMA3DRM30
Carrier typeFull CarrierNo Carrier
OFDM subcarrier spacing181.7 Hz41.66, 46.88, 68.18,
and 107.14 Hz
Effective Data Rate, 20 KHz Channel40.4 Kbps30.6 – 72 Kbps
Effective Data Rate, 10 KHz Channel20.4 Kbps6.1 – 34.8 Kbps
Channel bandwidth10 or 20 KHz4.5, 5, 9, 10, 18, 20 KHz
CodecHDC-SBRHE-AAC, xHE-AAC,
CLEP, HVXC
Operating Modes (QAM carriers and spacing)14
Protection Class (FEC)14
Features of HD Radio MA3 and DRM30

Both systems have 10 and 20 KHz channels available. This could be one feature used to mitigate adjacent channel interference, especially at night. In the US, physical spacing of transmitter sites helps prevent adjacent channel interference during the day. However, at night, half of the 20 KHz wide analog channel is in somebody else’s space and vice versa. Switching to 10 KHz mode at night would prevent that from happening and likely make the digital signal more robust.

DRM30 has additional advantages; multiple operating modes, protection classes and CODECs are available. Another advantage is the number of studies performed on it in varying environments; The Madrid Study,Ref 3 The All India Radio Study,Ref 5 Project Mayflower, Ref 4 and others.

Lets answer those questions:

  1. Are HDMA3 and DRM30 different? Yes, as the commenter stated, both use COFDM however, there are major differences in carrier spacing, symbol rate, and FEC. DRM30 has been designed at tested on HF, where phasing issues from multi-path reception are common. There are many configurable parameters built into the system to deal with those problems. My calculations of the Cyclic Prefix Length came out differently than those stated (I may have done it wrong), however, they are indeed different.
  2. Does the Cyclic Prefix Length make a difference in ground/sky wave interference? This is more difficult to answer. I would postulate that all of the configurable parameters built into DRM30 make it more robust. The various operating modes help mitigate phasing issues and the various protection modes help mitigate multipath reception issues. The only way to know that for certain is to do a side by side test.
  3. Which system would work better in high broadcast interference environments? Again, it is difficult to tell with out a side by side study. There have been numerous studies done on both systems; Madrid,ref 3 Project Mayflower, Ref 4 All India,Ref 5 WWFDRef 6 etc. In order to conclusively determine, one would have to operated HDMA3 on a station for a week, then DRM30 for a week on the same antenna system, with the same environmental conditions. Extensive measurements and listening tests would need to be performed during those tests.
  4. Is it worth it? Possibly. The big issue is the availability of receivers for both systems. Currently, only HD Radio receivers come as stock items in US automobiles. There are current and planned chipsets that have all of the digital radio formats built in (HD Radio, DRM+, DRM30, DAB/DAB+). If consumers want the service, manufactures will make the receivers. It would take a lot of effort to get this information in front of people and offer some type of programming that was highly desirable and available only on the radio. That is a big stretch.

Objectively comparing those two systems, I can see that both systems have advantages and disadvantages. There are some common items required for both systems; a reasonably well maintained transmitter plant, a newer solid state transmitter, and an antenna system with enough bandwidth so as not to distort the digital signal.

There are more receivers available for HD Radio, especially in cars. HD Radio MA3 is less configurable and therefore less likely to be misconfigured. There has been a lot of ink spilled in recent years about the declining number of radio engineers and the increased work load they are facing. Are there enough people with sufficient technical skills to implement and maintain even a basic all digital system? A topic for another post.

DRM30 is more flexible. Operating modes, protection modes and CODECs can be adjusted according to goals of station owners. There has been more testing done with all digital transmission of DRM30 using Medium Wave.

Are there enough reasons to allow a test of all digital Medium Wave DRM30 in the US?

Why not allow both systems and let the Software Defined Receiver decide?

References:

  1. HD Radio Air Interface Design Description Layer 1 AM Rev. G December 14, 2016
  2. Digital Radio Mondiale (DRM) System Specification, ETSI ES 201 980 V4.1.1 January 2014
  3. Digital Radio Mondiale DRM Multi-Channel simulcast, Urban and indoor Reception in the Medium Wave Band, Document 6A/73-E September 19, 2008
  4. Project Mayflower, The DRM Trial Final Report, BBC, April 2009
  5. Results Of DRM Trials In New Delhi: Simulcast Medium Wave, Tropical Band, Nvis And 26 Mhz Local Broadcasting, Document 6D/10-E March 28, 2008
  6. All-Digital AM Broadcasting; Revitalization of the AM Radio Service, FCC Fact Sheet, MB Docket Nos. 19-311 and 13-249, October 19, 2019

All Digital AM?

I have been reading, with interest, the saga of HD Radio on the AM (AKA Medium Wave) band. First question; if it goes all digital, will we still call it AM? Of course, there are other questions and concerns:

  • The proprietary nature of HD Radio, AKA MA3 or NRSC-5D as they are now calling it, is problematic. Xperi, the latest patent owner, currently (their word) has agreed to waive licensing fees for AM station owners who install their system. Is this a limited-time deal for early adopters or in perpetuity for all stations?
  • The NRSC-5D tests on WWFD, Fredrick, Maryland are hopeful, but as I pointed out before, it is one station with a well-functioning antenna system. Many AM antenna systems are defective either in design or due to deterioration. Is the FCC going to start policing the AM band again to cure these self-inflicted wounds?
  • Of course, the NAB wants zero oversight on the entire adventure. Under their proposal, small ownership AM stations would have a difficult time remediating interference issues from all digital co-channel stations by eliminating any required notification period, as proposed by the SBE.
  • The NAB also wants to nix a 1 Hz carrier frequency requirement, which would help with both the analog and digital interference issue, saying it would be too expensive. I disagree. In this day of universal GPS timekeeping, it would be easy to implement this on all modern transmitters, especially if they were already installing an HD Radio exciter.
  • Denis Jackson’s Radio World Article states that reliable coverage can be had out to 0.1 mV/m. This seems very, very optimistic given that ambient electrical noise (non-broadcast related) on the AM band is at very high levels and still climbing. Further, once the all-digital conversion starts, more and more co-channel digital interference will happen, likely cutting down that contour to a great extent. It works now but may not work later. These types of statements seem naive or perhaps disingenuous. Again, WWFD is one digital signal in a vast ocean of analog carriers.

While I am skeptical of some of the statements made in various articles and comments before the FCC, I do believe that converting the Medium Frequency band to all digital will have benefits. The BBC DRM tests carried out in 2007 (The Plymouth DRM long term trial) show that digital on MF can work. DRM has been implemented in various countries with good results.

Getting rid of the hybrid IBOC/Analog is a step in the right direction.

My concerns are the small owners who are still making a go of it on AM. Those guys still doing community radio and serving the public interest. If they choose to wait, are they going to get buried under a digital dog pile and then have to pay the full license fee later? Something like that might be the end for them.

HD Radio in and of itself is not the panacea for the AM band. Other things have to happen to make it work right. The SBE speaks extensively about ambient noise on the MF band. They are entirely correct. In addition, there are many, many AM stations that do not have compliant antenna systems. There are stations operating a DA-2 system full-time on the night pattern. There are stations operating a DA-2 full-time on the daytime pattern and power. There are stations that are supposed to turn off at night, which stay on 24/7. There are stations not reducing power to nighttime levels. The list goes on. Simply putting digital carriers on everything will not reduce station-to-station interference, especially at night.

I am cautiously hopeful that the FCC will look into the ambient noise problem, which simply cannot be over-emphasized. They would also need to re-invigorating the Enforcement Bureau. Since they closed down most of their field offices, it has been kind of a free-for-all out here.