Kaaaaaahhhhahnn!!!

I drew up a AM Stereo time-line [LINK] years ago but never really dug into the subject. It's time to revisit the war between Motorola and Kahn. First I should admit that there were more than two players. In D.C. we have two major parties, but there are a number of smaller groups that bear mentioning. It was the same with AM stereo. The top five were as follows:

1. Motorola (C-QuAM)
2.  Kahn-Hazeltine (Independent Sideband AM aka "ISB")
3. Magnavox (PMX)
4. Harris Broadcast (V-CPM)
5. Belar System

I am sure there were other patents...but those were the notable players and I'm sure I'll have the time to  fixate on obscure AM mode another day.Of those five, Kahn and Motorola were the 800lbs Gorillas. Barry Mishkind himself blamed the failure of stereo AM on the competition between the two "AM Stereo receivers went in the opposite direction, opening the bandwidth when the pilot was detected. Sadly, the Motorola-Kahn Wars all but doomed that mode." [LINK.] Barry knows what he was walking about as usual. AM radio was already in a precarious position and the failure to unify on a consistent standard put things over the edge.

Motorola's C-QUAM was invented in 1977 and was used widely in both the US and Canada and showed early signs of becoming a standard. But fast forward to 2014 and you can count on your fingers the number of American stations still using it: WLS-AM, WNMB-AM, WBLQ-AM, WIRY-AM, WAXB-AM and WLAD-AM. It's patents have expired and it is generally accepted as the international standard for AM Radio broadcasting despite being incompatible with IBOC. Despite those poor North American numbers... if there was a winner it was Motorola. The FCC finally adopted it in 1994.

Leonard R. Kahn's system didn't go quote as far. But he was a true believer. He was an AM radio evangelist. He once actually said "There is no limitation to the fidelity of AM radio.  From a mathematical standpoint, AM does better in frequency response than FM." This is complete malarkey of course. Because an AM radio station has a maximum bandwidth of 20 kHz, it is patently and inherently inferior to an FM station with 200 kHz of bandwith. On that comment he was wrong by a full exponential order.  More here and here.  But Kahn had more than 100 patents and his AM stereo patent was granted in 1958.He tested the technology on WQXR-AM in new York in 1956.

When Motorola was granted their C-QUAM patent they couldn't even steer it around Kahn's intellectual property. Patent US4172966 cites Kahn... twice Always the spoiler, his own ISB system was a compromise between double sideband (DSB) and single sideband (SSB) [ I know I am ignoring vestigial sideband (VSB) systems. Some of the same ideas re-appeared when he debuted CAM-D, his Compatible Amplitude Modulation-Digital system to compete with IBOC.] Still, Kahn did everything in his power to fight C-QUAM.


He criticized  the system for it's "platform motion" effects. While later revisions diminished the problem,it's stereo audio was susceptible to skywave interference.The result was a moving stereo balance with the audio "center" moving left and right randomly. It was true and even in the FCC order that declared it the standard they admitted that the problem was never completely resolved. But he also made a legal attempt to block Motorola from using its C-QUAM in the US entirely. In 1986 he filed a complaint claimed that C-QUAM violated FCC emission bandwidth specifications: specifically 73.44. He was right, but he was nit-picking. In the end C-QUAM won because they had the most radios on the market, and the majority of stereo AM broadcasters were using their system. The FCC adoption specifically mentioned other countries using the system. C-QUAM did not win because if technical superiority. It was a lesson that Ibiquity took to heart a decade later.

AM Radio Bandwidth (Part 2)

We left off Monday with the NRSC having to referee where the FCC had failed to tread. Fifty years of indecision had ruined an industry. The NRSC made a compromise decision that might rescue survivability from certain destruction.  It was the 10 kHz roll off.

Technologically the bandwidth reduction is accomplished with a low-pass audio filter.  It just chops off everything above 10 kHz. But there is a price to be paid for that steep roll off: group delay distortion aka envelope delay distortion. This is so hard to explain I am going to quote Dana Puopolo, who did a very good job in  radio World article in 2005.

"To recreate any sound accurately, the reproduction equipment must have flat frequency response, low distortion and noise and a flat time response. In other words, the entire audio waveform must arrive at your ear clearly, at the right level and in the proper time. Group delay is exactly what it says: delay. As you approach the cut off frequency of a filter, the frequencies begin literally to slow down as they go through the filter. This means that they arrive after the fundamental and other harmonics. Problem is, humans can hear time delay distortions and filter group delay quite easily. We usually perceive group delay as a "phasiness" to the audio"

Not all frequencies have this problem. Let me explain why. When you pluck the first guitar string it is tuned to "E" also known as 83 Hz. But it has harmonics. You hear natural harmonics at even intervals 165 Hz, 247Hz, 330 Hz, 659 Hz, 989 Hz, 1.3 kHz etc..(there are a mess of other harmonics at uneven intervals) This continues outward from the fundamental frequency beyond the limits of human hearing.

Radio wouldn't be interested in data above 20 kHz or below 20 Hz as those are the limits of human hearing. More subtly human hearing sensitivity isn't uniform, not between people, and not between frequencies. That is part of the reasons that the NRSC put the roll off at 10 kHz. That cut off  means that only the frequencies above 7 kHz experience group delay distortion. But it does mean that people with sensitive hearing can hear upper harmonics above that frequency arrive after the fundamental.

That was 1986.Now Clear Channel and Crawford both are advocating a steep roll off at 5 kHz. It cuts the bandwidth in half.  If you understood that last paragraph the problem becomes quite clear. Group delay distortion now occurs at 3.5 kHz in the center of human hearing sensitivity. (Humans typically have a sensitivity plateau around 3kHz.) Some of this can be diminished with modern digital filters. But this had no effect on the tuner. Those cheap radios that were problematic in the 1970s are still what we use. They have very poor high-frequency response perhaps down 6 or more dB at 4 kHz, some even roll off at 2kHz.  this compounds the problem with a result of severe audio artifacts. In other words.. It sounds kind of crappy.  It's the same spacing as they use in shortwave radio.

 Their goal in reducing it to 5kHz is dubious. It allows the station to maintain a higher average loudness. It further reduces interference in a frequency band that's loaded with it. It may even open up some markets for some power increases. It also allots space to shoehorn in HDAM.  That's why Jeff Littlejohn at Clear Channel and Cris Alexander at Crawford Broadcasting have already shopped their AM talk stations to 5 kHz and music stations to 6 kHz. Notice their talk and music have been rolled off at different frequencies. This means that on a Clear Channel owned station, a Talk radio station sounds only 1kHz better than a land line phone call. 6kHz for music is unspeakable, sub-MP3 audio quality. For reference, remember that FM radio has up to 15kHz.


In the book The Age Of Electronic Messages author By John G. Truxal rhetorically asks the question "Why did the United States adopt these regulations that doomed AM Radio to music of poor quality?"  He then spent a few paragraphs describing what it would really take for an AM station to have high audio quality. I'll summarize.  To reproduce the full range of a CD quality recording you would need a 36 kHz allocation. That would reproduce frequencies all the way up to 18,00 Hz. The problem is that then AM stations would need to be 36 kHz apart. It would require reducing the number of AM radio stations by about 66%. That really underlines the source of the problem.

The problem is human, not engineering. We have tried to find solutions in compromise. Physics isn't interested in placation. Reality is not negotiable. Listenership is already sliding. Trading around different painful compromises is no solution. The refusal to commit fully to one solution is the problem and always has been the problem. FM achieved ratings parity with AM in 1979.  It's all been downhill for AM since then. My assessment is that it will continue to be the problem until no one is listening anymore. ...Or more cynically, until the remaining audience is old enough that they can't hear the problem anymore.

AM Radio Bandwidth (Part 1)

It is a simple engineering argument over AM audio frequency response. But the topic is so conceptually above the laypersons head, that very questionable decisions are being made in an arena where regulation should be making the final decision. I've kept the specifics out of the preamble and I'll begin in the arcana of AM history.

The problem is nearly as old as radio itself.  It's called "splatter" which is short for Spectral Splatter. This is when the broadcast includes noise at frequencies other than the frequency of the carrier wave. If there was only one radio station this wouldn't need to exist, but we have 14,000. So much like the suburbs, where your lawn ends, another neighbors lawn begins.  Because the goal is to have as many choices as possible, we want to use the existing bandwidth efficiently.  But you cant put your ficus bush on your neighbors property.  Radio is much like this where stations are squeezed in together such that splatter will occur on adjacent channels and not vacant space. Essentially, there is no vacant space. This situation requires a referee (the FCC) and a lot of regulations. In radio, FCC regulations require radio signals be contained in a particular frequency band. This is defined by a "spectral mask". OK, new word. It's also called a channel mask or transmission mask.

"...a mathematically-defined set of lines applied to the levels of radio transmissions. The spectral mask is generally intended to reduce adjacent-channel interference by limiting excessive radiation at frequencies beyond the necessary bandwidth. Attenuation of these spurious emissions is usually done with a band-pass filter, tuned to allow through the correct center frequency of the carrier wave, as well as all necessary sidebands."

The key phrase there is "all necessary sidebands."  This is the topic over which engineers have been arguing. the carrier wave is what you tune the radio to.  If you're listening to 100.1 FM, on a graph 100.1 FM is just a line, or a point. Data takes up space.  In the most rudimentary sense this is referred to as bandwidth. Here is a picture of an FM HD signal to help visualize the relationship. The sidebands are mirror images and the carrier wave a dividing line. How far away from this center point the side bands can be is the point of contention. Enter the NRSC.

Right now AM bandwidth is fixed at 10 kHz as per the NRSC standards that were set November 20th 1986 read it here. The ruling was sort of late to the AM radio game. FM radio had already overtaken AM radio by the early 1980s at least in sheer numbers. FM had them on fidelity, and bandwidth  was partially why. I'll quote the December 1976 issue of Popular Mechanics to summarize the situation:

"Most of the inexpensive portable or table radios... are too insensitive to pick up any but the strongest signals clearly, are plagued by interference, and are limited by tiny speakers that produce only tinny sound. Even the AM sections of component high-fidelity tuners and receivers are frequently cheap, poorly designed circuits... the fewer listeners who can hear the difference at home between  good and bad AM broadcasts, the less motivation AM stations have to clean up and improve their signal."

AM stations are spaced 10 kHz apart. that sounds fine except that the FCC allowed AM stations to broadcast sidebands on some stations up to 30 kHz wide!  That's 15khz to each side  of course. the math is obvious, broadcasting more than 20kHz increased the odds of interference significantly. But there was a second problem. Most AM radios tuned much more narrowly than 30 kHz.  they did so for 2 reasons. First is was cheaper, second it reduced interference by avoiding second adjacent stations. But that also meant not receiving the stations high frequencies. It made everything sound muddy.

Stations fought back. They used an audio process called "pre-emphasis" to boost high frequencies.  It's wasn't a radical new technology.  The RIAA equalization curve on 33 rpm and 45 rpm vinyl records used pre-emphasis. it can also be used in digital processing to reduce bit errors. the downside was that in the already narrow world of AM bandwidth, it caused even more interference. Makers of consumer radio tuners narrowed bandwidth even further to reduce that interference. By the 1980s the end result of this downward spiral is that most AM radio tuners reproduced 4 kHz of bandwidth. That's only a slim margin better than the audio quality of a land line telephone (3.4 kHz.) Consumers were driven away from AM toward FM. It was about then that the FCC OK'd AM stereo. It was the perfect storm.

The NRSC tried to salvage a radio service from this nightmare.  The NRSC studied the problem and came out with a simple compromise: the 10 kHz steep audio roll-off.  ...more in part 2

The binaural Emory Cook

For a number of years, Emory Cook was considered a truly exceptional audio engineer. He was born and raised in Albany, NY and attended Cornell University. He worked for the Audio Engineering Department at Western Electric. He was a strong proponent of binaural sound, an inventor and audiophile. He once described binaural sound thusly:

"Stereophonic recording differs from Binaural in that the microphone placements are selected for loudspeaker reproduction. Binaural properly applies to a two-channel system designed for headphone reproduction. It thus requires the use of two channels fed by microphones spaced about seven inches apart."

Those magic 7 inches represent the average distance between a pair of normal human ears. it's the founding idea behind binaural sound. It is supposed to put the listeners perspective sonically where the sounds on the recording or broadcast originated. I consider it a subtype of stereo sound. Stereo sounds being if nothing else.. at least less specific. More here.

It's strange, but binaural sound actually predates stereo. In 1881 Clement Ader installed pairs of carbon mics on a Paris opera stage for telephone subscribers to listen in. How is this separate from the evolution of stereo? It's not. They're inextricably linked. Every step in the evolution of stereo sound can also be claimed by the evolution of binaural sound. The only difference is snobbery. There is a gri-gri quality to binaural sound that stereo lacks. But let's get back to Emory. There was a lot of gri-gri to him as well.

Emory created a record player with two needles meant to play records with two parallel grooves. He founded Cook records in 1949 and eventually put out more than a hundred binaural LPs. His plant was based in Stamford Connecticut. Emory was using his personal brand recognition to hype a series of binaural LPs: Sounds of the Sea, Nightmare in the Mosque, Speed the Parting Guest. He demonstrated them at the Worlds Fair. They're all over eBay now for the kitsch.

But there were also radio broadcasts were live like Toscanini, WQXR string quartet and the Godina opera hour. But this was 1952. stereo sound was entirely new in broadcasting. WQXR was achieving "stereo" by using it's using its AM and FM stations towers as separate Left and Right audio channels. Was it stereo, was it binaural? I don't distinguish a difference. Binaural enthusiast will tell you this was the first binaural broadcast. I think it's bunk. In 1925, on 5XX the BBC had broadcast stereo with the Left channel on medium wave and the right channel on long wave. That's 27 years before WQXR. WGN-AM and WGNB-FM did the same thing in 1952 just a few months before WQXR. All they're beating their chests over is microphone positioning in the source audio. It's bunk; clever bunk, but bunk nonetheless.
The irony is that in the process of supporting the bunk idea of binaural audio the very educated and clever Cook actually made other developments. He made microphone and amplifier improvements that made it possible to record audio above 20,000 cycles, he even developed a process to press vinyl in a powdered form to reduce surface noise. Previous to this they were always pressed starting with a preheated puck of vinyl, a technique based on shellac 78s. He called the new technique “microfusion.” Sadly it didn't catch on.

Emory Cook died in 2002 at the age of 89. Emory donated his master tapes, patents, and papers to the Smithsonian Institution in 1990. Obit here.

Reprocessed from Monophonic

The great conversion from mono to stereo was traumatic. In 1958 all AM stations were stillmono as were FMs. But in just a few years, home stereo systems were switching over to stereo even without a clear technical standard. The reason was that radio was feeling a little peer pressure in the stereo cabinet.

 LPs were going stereo. Western Electric had pioneered the Westrex process called 45/45, a single groove stereophonic system. The important part is that existing monophonic equipment could still play the Lps ensuring instant consumer acceptance. It worked. Western Electric was the manufacturing arm of AT&T for the better part of a century. They started out in the 1850s making typewriters.

In the 1970s, the now flat-sounding mono records were commonly rereleased with "enhanced" sound. this was also called "Duophonic" sound after the Capitol records process. These were marketed as stereo versions of the original releases. But the monophonic master tapes had no stereo separation. So they had to fake it. The stereo effect was created through a couple remarkably simple techniques. Some audio filtering was used to separate out certain sounds to pan them. This usually produced noticeable audio artifacts. Also common were slight adjustments in EQ and phase which is what RCa seemed to focus on. An offset of 20 and 50 milliseconds was another very rudimentary change that mimicked the stereo effect.Worse yet was over-dubbing. A small trio would be brought into the studio to overdub minor parts to add stereo sound to the mono recording. There is an abominable Roy Orbison LP out there with a dubbed in accordion track that is a testament to the general badness of this idea. Also interesting is that as Stereo picked up, these old mono recordings went out of print. It left both radio and record collectors forced to either play the new clunky "enhanced monophonic" Lps or move on. Mono was essentially dead by 1978, but enhanced mono dragged out straight through the 1970s. Some Labels carried Mono, ST (Stereo) and DT (Duophonic) notations, but the collections were usually a mix of all three regardless of labeling.

AM Stereo Time Line

Ironically Stereo AM produces higher quality audio than IBOC AM. Yet Am stereo died struggling like Betamax did, in front of everyone and there was nothing we could do to save it. Stereo sound reproduction was first experimented with in the early 1900s, and was put into use in motion pictures around 1930. However, Stereo sound did not gain real market penetration until the introduction of the Stereo LP in 1957. More here.

Early experiments with Stereo radio broadcasting involved two separate stations broadcasting the Left and Right audio channels. Consumers did not accept this This Rube-Goldberg set up as it was just as ridiculous as it sounds.

In the early 1980s four competing AM systems went on air. These were:

1. Motorola (C-QuAM)
2. Magnavox (PMX)
3. Kahn-Hazeltine (ISB)
4. Harris Broadcast (V-CPM)
5. Belar System 

AM Stereo timeline Highlights:

• 1960 - AM Stereo first demonstrated on XETRA-AM, Tijuana, MX, using the Kahn ISB system.
• 1963 - WHAZ runs a stereo program on eight AM stations, four on each channel.
• 1984 - The FCC begins AM Stereo testing with five systems. Initially they select the Magnavox system. Their research is immediately accused of being flawed and incomplete.
• 1993 - FCC makes Motorola's C-QUAM the AM stereo standard. This sets off another series of lawsuits and accusations resulting in the FCC deciding that the marketplace should decide. The marketplace decides to continue fighting like children and this becomes a death blow to the possibility of AM stereo.

There are still over 100 stations still chugging along with stereo broadcast...
one that no one can receive, they are listed here.