In order to get to the root problems of AM (aka Medium Wave, or Medium Frequency) broadcasting, a bit of history is required. For the sake of brevity, here is the cliff notes version:
Early broadcasting services were entirely AM and heavily regulated by the FRC and later FCC
FM broadcasting was introduced in the late 1930s experimentally, then commercially circa 1947
In 1946 the FCC relaxed its regulations allowing many more AM stations to be licensed as both class II (currently class B regional) and class II-D, II-S, and III-S (currently class D) stations. Between 1946 and 1953 the number of AM stations more than doubled from 961 to 2,333
In spite of FM’s technical superiority, AM remained dominant until approximately the mid to late 1970s when the FCC forced FM stations to end simulcasting with co-owned AM stations
Broadcast deregulation came in small waves at first; programming rules, business rules, some technical rules, and operator license requirements were done away with, and enforcement of other rules became more selective
Deteriorating antenna systems, splatter, modulation wars, declining technical resources, and increased electrical noise created interference issues
The electrical noise floor gradually increases as more electrical appliances, street lights, fluorescent lights, and other intentional emitters increase
Radio manufacturers responded to consumer complaints by greatly reducing the audio bandwidth of their AM receivers
Broadcast deregulation greatly increased in the 1980s
The FCC voted in 1980 to limit skywave protection of clear channel (class I or A) stations to within 750 miles of the transmitter site allowing former daytime-only stations to stay on at night which increased interference
AM Stereo is implemented in 1982 to improve quality and compete with FM broadcasting. Competing systems are proposed, FCC does not mandate a standard, lets the market decide, and the technology dies off
The National Radio Systems Committee (NRSC) is formed and comes up with a standard (NRSC-1) that restricts AM broadcast audio to 10 KHz or less, mandates yearly measurements
Ownership rules are loosened somewhat in 1994, then greatly in 1996
The expanded AM band (1,610 to 1,700 KHz) is opened up in 1997 to existing AM broadcasters. Once stations are licensed to operate in the expanded band, they are supposed to surrender their former licenses, few do
The great radio consolidation takes place; from 1997-2004. Synergy is the word of the day, stations are overvalued in multiple transactions which created a debt bubble
Skywave listening is mostly depreciated as an acceptable communications method by the industry
The introduction of IBOC hybrid analog/digital broadcasting in 2002 greatly increased the adjacent channel interference issues. Sidebands out to ±10-15 KHz of the carrier are introduced with power levels of -16dBc. For a 50 KW station, this equals approximately 2,500 watts of power transmitted on each of the adjacent channels. Analog audio of stations transmitting AM IBOC is restricted to 5 KHz, background digital noise is often present in analog audio, further degrading the quality
Inside electrical noise greatly increases as compact fluorescent lamps (CFL) and LED lamps become popular energy-saving measures
Night-time operation of HD radio was permitted in 2007 creating greater interference problems to distant adjacent channel stations
There are 4,738 AM stations licensed, 89 are silent, approximately 210 transmit HD radio, and approximately 66 (mostly class A and B stations), transmit HD radio at night
There is not any one development that can be singled out as the smoking gun that killed the AM broadcast band, it is rather, a death from a thousand cuts. Because of heavy debt loads, technical, programming, promotional, and personnel resources are directed away from AM stations (and FM stations too). After the staff was reduced and news departments eliminated, AM stations became a dumping ground for mediocre satellite-syndicated talk programming. Eventually many also became a technical nightmare due to deferred maintenance.
There can be little doubt, AM broadcasting is a tough business to be in. In spite of all of that, however, there are several AM stations that are not merely surviving but thriving. What does it take to be a successful AM broadcaster in 2013? There seem to be several common threads, but the two most common are good technical operations and local programming.
After reading this article in Radio World it seems the all-digital AM testing completed last December was “nearly flawless.” This comes as no surprise considering that WBCN is owned by CBS, also an iBiquity investor. Could there really be another result? I think not. But let us examine the technical aspects of the WBCN test itself.
WBCN is on 1,660 KHz in the expanded part of the AM band. According to the FCC database, it transmits from a single 90.7 degree tower. As such, the tower is likely either broad-banded already or easily modified to be. Also according to the FCC database, there are eight other stations licensed to 1,660 KHz, all of which transmit with a power of 1 KW at night. This eliminates much of the interference issues found on the rest of the AM band. It can be further noted, the problem with electrical noise is most prevalent below 1,000 KHz. There is little wonder in the nearly flawless results.
From a technical standpoint, this is about as favorable a testing configuration as can be conceived for AM IBOC. If AM HD radio did not work under these test conditions, then it would never work at all. The actual data from the tests has yet to see the light of day and it may never be released. This is likely due to the same reason the NAB will not release its technical improvement study on AM; we simply won’t understand it.
Near the end of the article, someone (it is not exactly clear who) asks the NAB, “Why the opacity?” For which the answer given is “to get stuff done.” There is a fair bit of hubris in that statement. Is the NAB now the technology decider for the rest of us? I think not. Shutting out everyone but a very select few rightly causes suspicion, something that the Radio World article acknowledges.
Accurate, real-world testing involves more than using one technically favorable test subject. In fact, the tests should be run in the most technically challenged environment to present meaningful data points in real-world conditions. Stations like a six-tower directional on 580 KHz, a 190-degree tower with a folded unipole on 810 KHz, or pretty much any class C AM station at night time. These types of tests will represent at least a few of the existing antenna systems and stations. Will that happen? It depends on whether the FCC will hold somebody’s feet to the fire and demand meaningful testing.
Much ink has already been spilled by various trade publications debating the future of AM broadcasting. Most take the position that there are several technical issues that make AM broadcasting problematic if not downright untenable. There are indeed some technical issues with AM when compared with FM or IP-based audio distribution. There are also several ways that AM broadcasting is superior to both FM and IP-based audio distribution. The truth is that AM broadcasting’s issues are complex and involve technical, regulatory, and operational considerations.
These can be broken down as follows:
AM is prone to electrical noise interference
AM is prone to co-channel and adjacent channel interference
AM has inferior bandwidth and thus the audio quality
AM has poor signal quality
AM has a low or no market share
All of these problems conspire to make AM broadcasting unprofitable, or so the narrative goes. Does all-digital AM HD radio really solve any of these problems? From the WBCN test alone, the results are inconclusive.
Transmitting a signal in digital format does not make it immune to noise or interference. It simply masks the interference until the noise floor becomes too high causing excessive bit errors, at which time the receiver mutes. Thus, with AM HD radio in a noisy environment, the listener will not hear static, that much is true, they may not hear anything at all. Is this all-or-nothing reception an improvement?
AM broadcasting audio bandwidth problems are mostly self-inflicted. AM stations created loudness wars in the 60s and 70s, causing splatter and adjacent channel interference on older, cheap diode detector-type receivers. Receiver manufacturers responded by limiting IF bandwidths to 3-4 KHz, slightly better than telephone quality. The industry came up with the NRSC-1 standard which limited AM bandwidth to 10 KHz or less. For a long while, AM radio receivers remained very poor. This appears to be changing with newer receivers that are both more selective and more sensitive. My Toyota has a Pioneer radio which has good bandwidth on AM. Is it as good as FM? No, but it is certainly listenable, especially if no other station is playing that style of music.
That brings me to programming, which is the real crux of the issue. Continued in part II.
FM and AM broadcast radio processing has gone through many iterations. At first, the main processing function was to limit the input audio to a transmitter and prevent over-modulation. This was a particular problem with early tube-type AM transmitters, where over-modulation could create power supply overloads and kill the carrier while engineers scrambled around resetting things and hopefully pressing various buttons to get the transmitter back on the air.
Over the years, processors incorporated not just limiting, but compression, gating, equalization, clipping, and so on all in an effort to keep ahead or at least abreast of the station across town.
Today, broadcast air chain processors come in all shapes and flavors. In addition to that, internet streaming stations have their own unique set of issues to deal with. The top-of-the-line Telos Omina or Orban Optomod systems are great, however, they can set one back a pretty large sum of money. Enter then, the Stereo Tool PC based software processing program.
Stereo Tool sofware screen shot
The first difference between, say the Omina and Stereo Tool is the end user decides the hardware and basic operating system. The second difference is Stereo Tool comes with a free trial. Then there is the price difference, which ranges from about $48.00 US for the basic version, to $161.00 US for the basic FM version and finally $269.00 US for the full version (actual prices are in Euros, which will fluctuate day to day and the credit card company will likely charge an exchange fee). Add to that a medium-speed (2 Ghz) Intel Pentium4 or better computer, 1 Gb or more of RAM, good sound card and it all comes out to a reasonably priced audio processor.
Here are some of the specific features for broadcasting:
The idea of PC-based audio processing is new and interesting to most of us. The designer and owner of Stereo Tool, Hans van Zutphen, was nice enough to answer a few questions I posed to him via email:
PT: What prompted you to write audio processing software?
HvZ: Since I was very little I’ve always wanted to have my own radio station. I remember playing with walkie-talkies and trying to receive their sound on a real radio when I was about 8 or 9. I never really did anything with it until I found out in 2001 that you could easily start a webradio station – I actually found out because I was listening to a pirate station in my car which turned out to have a stream; within a week my own station was online.
Of course, I needed a bit of processing for it, and I wrote some command line tools – a single band compressor, a stereo-to-mono converter that didn’t cause any loss of audio (I was broadcasting hard trance on a mono 56 kbit/s stream, and this was the only way to get a decent sound out of it), and sometime later a multiband compressor.
In 2004 I left the company I worked for (ASML, they make machines to make computer chips, customers are companies like Intel, AMD etc.) to start working for Philips Healthcare, where I was going to work on image processing for X-Ray systems. I had 2 months of ‘spare time’ between those jobs, and I wanted to learn to program in Visual C++, so I decided to a GUI around my command line tools, and make a Winamp plugin out of it. I called it ‘Radio Tool’. I never really planned to do anything with it, it was just an exercise project.
About a year later I came across the Winamp site again and I saw that you could upload plugins. So I uploaded my program, now renamed to ‘Stereo Tool’ because a Google search for “Radio Tool” gave far too many hits. Within a week there were over 1000 downloads and a while later it surpassed 90,000. At that point I decided to create a new version, Stereo Tool 2.0.
For quite a while this remained a hobby project, I occasionally worked on it for a few months and then I wouldn’t look at it for months. But at some point I was approached by someone people who worked at a “real” (FM) Dutch radio stations who asked for some extra features – he couldn’t get the audio loud enough, and that’s how I got into clipping. Things started to get better, I learned more and more about processing, the number of downloads increased and people became more and more enthusiastic about it. At some point, after reading something about how an FM stereo signal looks, I thought it might be possible to output a stereo signal with a 192 kHz sound card, so I bought one and did some tests and it worked that same night, and within a few weeks I added RDS.
PT: Do you know, approximately, how many stations (AM/FM/internet) Stereo Tool is being used on?
HvZ: FM: About 500, ranging from small community and pirate stations up to large nation-wide stations which run Stereo Tool at a dozen transmitter sites. Streaming: Not sure, but definitely over 1,000, probably a lot more.
PT: I have read through the forums on your site, Stereo Tool looks like a very complete processing system. Any plans for new features, future upgrades, etc?
HvZ: Yes. I’m currently working on a new multiband compressor. The multiband compressor in Stereo Tool is still based on the code that I wrote in 2001 for my webradio station, which in turn was based on an even older version that I had used on 8-bit audio. It also has far too many bands. Because of this, the multiband compressor is currently the weak spot of Stereo Tool. In the last weeks, I have made a new single-band compressor that sounds a lot better, it actually outperforms other compressors I have tested, and I expect great results for the new multiband compressor, which will also have fewer bands. Something else that I’ve been planning for a long time is a composite clipper, which will add 1-2 dB of extra loudness and especially better highs. Stereo Tool can already be louder with good audio quality than nearly any hardware box on the market (see for example this video, Radio 538 uses an Orban 8600 http://www.youtube.com/watch?v=4VpfcqUPQys – unfortunately due to the mpeg compression it’s a bit difficult to compare but listen for distortion ) – but there’s always room for improvement.
PT: What are the advantages of a PC software-based processor vs. a hardware-based (e.g. Omni or Optomod)?
HvZ: Ah, good question. Not sure if it’s the right question… With processing, a lot of things come down to taste, and there are several stations that have replaced their hardware processing with Stereo Tool not because it’s software and PC based but because they preferred the audio that comes out of it. Stereo Tool is also one of only 2 processors that contain a de clipper (the other one is the Omnia 9, I licensed my de clipper to them). For a demo of the declipper see: http://www.youtube.com/watch?v=oqOljvx9KaM
Also, Stereo Tool contains a stereo and RDS coder, but most other processors don’t, so instead of having a whole bunch of devices everything can be done in a single PC, which also results in better quality. Recently I added a new feature that enables synchronizing multiple FM transmitter signals that all connect to a simple Shoutcast stream (video: http://www.youtube.com/watch?v=GYQ5CYs0ZX8 ), so you also don’t need any streaming hardware anymore.
Of course, there’s the price. A hardware box that gives “similar” quality (of course every processor sounds different, and it’s a matter of taste, so it’s difficult to compare, but I’m assuming that things like low volume levels, gain riding, distortion, and lack of clarity in the highs are bad) easily costs $10,000 or more. And you can always easily upgrade to new versions. If you already have a PC with enough spare processing power you don’t need to buy anything.
I know that some people at radio stations are ‘afraid’ of using a PC in their processing path, but based on feedback I get from the stations that run my software it’s completely stable – and of course, if a PC does break, you can replace it with any fast enough PC you have lying around – you just need to put the proper sound card in.
But for development, the advantages are huge. If you use DSPs, it’s usually a lot of work to even make a very small change. When I worked at Philips Healthcare, the image processing that had been done – without many changes – on DSPs for many years was being converted to PCs because of the speed of development and the price of hardware. Once the conversion was finished, the development speed increased dramatically and 2 years later the image quality had improved beyond anything that was imaginable with DSPs. PCs get faster every year, and you don’t have to do anything for that – for the same price the processing power that you can buy roughly doubles every 1.5 years, and if you pay more you can get even more. If you use DSPs, you have to do a lot of work yourself, you cannot just ‘buy a faster DSP’. Testing things is very easy, I can write some code that does something new, post it on my forum and I’ll have feedback from users the next morning – with DSP that’s a LOT more difficult and it takes a lot more time. I’ve learned by now that everyone hears things in a different way, and occasionally there are groups of people who hear something they find very annoying while many other people (often including myself) don’t hear anything wrong with it at all. Especially in cases like this, it’s really great to be able to quickly send new versions to several people all around the world for testing.
PT: Are there any particular sound cards that work better with Stereo Tool?
HvZ: Yes. For the best results, use the Marian Trace Alpha, with the ESI Juli@ as the second-best choice (it needs calibration).
Thank you very much, Hans, for the interesting insight.
Check out the videos, especially the de clipper video, which is quite amazing. That will clean up all but the most ham-handed DJ mistakes.
PC-based audio processing software is a great solution station on a limited budget that cannot afford high-end air chain processors. There are many LPFM’s, Part 15 stations, and others that can get great-sounding audio and RDS for a very reasonable price. Currently, the AM settings do not allow asymmetrical modulation, which is more of a US thing. There is some talk of adding it in a later update.
In keeping with the theme “Take pictures now, because someday these stations may disappear,” I was out at WVOS-AM in Liberty, New York today removing some old studio equipment. The former studio building is going to be leased out as office space. The call letters mean the “Voice Of Sullivan” county, where the station is located. Urban legend has it, the station’s claim to fame is that while Max Yasgur and Michael Lang were negotiating the use of Yasgur’s nearby farm for a music festival at the local diner, the diner staff overheard and called the radio station. Thus, WVOS-AM was the first to break the story of Woodstock.
WVOS-AM transmitter building and former studios
The station originally signed on the air in 1947 from this location with a power of 250 watts. At some point, the power was upgraded to 1000 watts along with all the other class C AM stations in the lower 48 states. The original building has been added onto and recently resided. An FM signal was added in 1967. These studios remained in use up to December of 2005, when the stations were moved into the co-owned WSUL studio facility in Monticello, NY.
WVOS-AM tower, along NY Route 17, Liberty NY
This is the original tower, which is 194 feet (59.16 meters) tall. As such, it is no longer required to be lighted or painted. This is the tower that is on the right-hand side of NY Route 17, just as one is entering the village of Liberty.
Lobby, former WVOS studio building
The former studio building itself is in remarkably good condition. Oftentimes, when a studio gets moved, the old equipment is abandoned, the heat is turned off and the place is shuttered. After years of neglect, these buildings are usually in very rough shape. Not so with this building.
Nautel Amphet 1, WVOS-AM, Liberty, NY
The transmitter is a Nautel AMPFET 1, short version. Its serial number 132, which, I don’t know the year of manufacture but I’d bet it was before 1990. At some point, an add-on matching unit was installed to better match the transmitter to the tower. In my mind, transmitter-to-antenna matching is best done at the tower with an ATU. I don’t know why the matching unit was deemed necessary.
Gates BC1T transmitter, WVOS-AM Liberty, NY
The backup transmitter is a Gates BC1T, made in 1968. The nice thing about these old tube transmitters is you can match them to almost anything. On more than one occasion, I used a Gates BC1 series transmitter with a horizontal wire, while a tower was being replaced.
WVOS 1240 KHz
It looks like the roof might have leaked onto this transmitter at one time.
When I was there, the station was playing some sort of Hot AC format. There is no mention of the AM station on any company-owned website. It appears to be changing formats often as several sources have it listed as either Spanish talk, ESPN sports or country music. Seems to be a throwaway, at this point.
