Success of a Broadcast Medium: The Muzak Transmission Process

By Andy Oram
November 18, 2009

One successful story is often omitted from surveys of broadcast media: Muzak, a corporation that has just celebrated its 75th anniversary. A friend of mine, who worked for the company in the 1980s, got me interested in several intriguing facets Muzak its approach to content, its business model, and its technical means of dissemination. I'll focus on the last item here because I'm writing for a technology blog. I'll draw on background give to me by staff from the company.

Although the constant butt of jokes, Muzak has been a channel for hundreds of leading American musicians and can promise its clients happier customers and improved worker productivity (not in jobs like the ones I've held, but jobs that people wait through the day to go home from). The famous Dorsey Brothers, Tommy and Jimmy, who were highly respected by Charlie Parker, played for the Muzak company for years.

A hotbed of innovation in telephony and radio

The urge for technical innovation behind Muzak started long before it saw the light of day. The company's founder, George Owen Squier, served earlier as an army general who invented innovative ways of transmitting information both inside and outside the armed forces.

Squier also invented multiplexing over phone lines, using it to transmit high-frequency signals over wires that were strung for lower frequency transmission. (This sounds like a century-old version of the technique used for Asymmetrical Digital Subscriber Line (ADSL) transmissions, the critical hack that phone companies used in the 1990s to catch up with cable companies and offer a relatively high-speed Internet connection to their customers cheaply over existing copper lines.)

Squier patented his work in 1911 and donated his patents to the American people, allowing anyone to use the technique--although he expected it to have only noncommercial uses, and was upset to see that companies made money by using the technique to allow multiple voice calls over a single wire.

In the 1920s, Squier used his technology to broadcast music over wires, but turned to the radio medium in 1934 when he founded Musak.

Content production and selection

From the 1930s through the early 1960s, the American music business was homogeneous easily satisfied by broadcasting the popular swing bands. When the musical revolution of the 1960s hit, followed by the public embrace of diversity (for instance, the growing popularity of various forms of Latin music), the company realized they had to branch out.

Rigid copyright laws prevented them from licensing and rebroadcasting original recordings, so they hired their own orchestras to record non-vocal versions of current hits, producing the "elevator music" sound--they prefer to call it "environmental"--that most people think of when they hear the company's name. This environmental music is still one of the hundred-odd channels they offer, because (as the company representative told me) "it's wildly popular in Japan."

I doubt that many of the people who have heard this traditional form of Muzak noticed the rigid construction of its audio stream. After all, the whole point of the service was to remain in the background and not impinge on people's consciousness. But the Muzak corporation had an agenda, and their song sequence implements it. (Much of this section, I should warn you, comes from my friend's recollections and could not be verified by company staff because it's so old.)

Each song was classified at a particular energy level, which could be carefully modulated through choice of orchestration, rhythmic elements, and melodic elements. The three-minute songs were then arranged in groups of five to make fifteen-minute segments that began with a very calm mood and built incrementally to a relatively high-energy peak. The whole sequence restarted after fifteen minutes with a new set of songs--all day long.

Studies by industrial psychologists demonstrated that the fifteen-minute segments, with each selection increasing in stimulation value, gave a feeling of forward motion and an energy lift to people working in offices or factories. The studies documented greater work productivity when people were exposed to Muzak background music.

In 1984, changes to copyright law allowed Muzak to license music recorded by others. This led to the proliferation of Muzak channels--know as "core programs"--of all types as well as custom disks. They can give you a selection of 500 or 1000 songs in a genre of your choice (even hip-hop), and update it every month. If a genre is very current and experiences a lot of churn among artists, Muzak will update their offering relatively frequently.

Broadcast business and technology model

What surprised me most about Muzak was its use of radio broadcasting for many of its most prominent years. Currently, as I have indicated, the company distributes a variety of formats in a variety of ways. But for much of its history, Muzak was exactly the same in every location. The jingle you heard in a hotel lobby in San Francisco would be the same one an office worker was listening to (or absorbing unconsciously) two thousand miles away. Some of this section, once again, comes from my friend and could not be corroborated by the company representative.

One interesting bit of technology history is the way Muzak used standard FM radio frequencies without interfering with their regular transmissions. They did this through a "side channel," also known as storecasting or the SCA. This technology has nothing to do with the metaphorical use of the term "side channel" by security experts to denote an attack that works its way around normal communication mechanisms. I couldn't find any help understanding the term from three popular search engines, because any possible references to the technology behind "radio" and "channels" were totally drowned out by pages about commerce (an interesting metaphorical example of interference in action).

The Wikipedia page on FM radio provided a better signal-to-noise radio, but things really got crackling when I walked down to my town's public library and picked up Elements of Radio, Sixth Edition (by Abraham Marcus and William Marcus, published by Prentice Hall, 1973).

An FM channel consists of 75 Kilohertz (KHz), but only half that range is needed to hold a radio signal of adequate sound quality. Whatever the FM number is--for instance, a Boston-area station at 92.9 was used for Muzak--this number can be considered the central 38 KHz frequency in the 75 KHz band, and the rest of the band is arranged around it as follows:

0-15 KHz
This holds the sum of the frequencies from the left and right channels and is called the L+R signal. A monaural receiver can demodulate this signal.
19 KHz
This is a pilot signal, which is used to reproduce the central 38 KHz frequency that the tuner uses to synchronize with the radio station. The exact purpose and mechanism for using the pilot signal is irrelevant to this blog, and I might not be able to describe it accurately anyway. The 19 KHz signal is isolated from the rest of the signal to avoid interference. That is, nothing lies in the 16-18 or 20-22 range.
23-53 KHz
This large band, centered on the 38 KHz frequency, fills out the stereo signal. Called the L-R signal,this band consists of the right channel frequency subtracted from the left channel frequency. The Wikipedia page I referred to includes a fairly nimble description of the signal's use: "A stereo receiver will add the L+R and L-R signals to recover the Left channel, and subtract the L+R and L-R signals to recover the Right channel."
59-75 KHz
This is the "side channel" or SCA used by Muzak and other broadcasters for specialized uses, holding the rest of the high frequencies that are not needed for ordinary broadcasting.

As far as I can establish (once again, historical evolution is hard to corroborate officially), when satellite transmissions because possible in the 1970s, Muzak used them to transmit its signal to local radio stations in each area. Eventually, the company stopped using radio stations as intermediaries. Customers who had the physical and financial means to mount satellite dishes took their audio directly from Muzak or one of its franchises.

Customers who couldn't mount a satellite would get Musak on other media. Muzak used cassette tapes when those were cutting-edge, then invented their own proprietary disks, similar to CDs but incorporating encryption to prevent copying and reuse.

Currently, Muzak's delivery options include satellite, disks, and the Internet. Satellite and Internet users download new material in the background and then play it directly from the Muzak device, so bandwidth demands are low. Normally, customers choose to download new selections each night, so the device doesn't interfere with routine network use during business hours. Muzak's devices are now quite small (they weight 11 ounces and can fit in the palm of the hand) and hold flash cards that store a day's worth of music.

A final inspiration: cue the strings

Computer programmers and Internet protocol designers build on a tradition that, decades earlier, found innovative ways to use extremely limited communications resources. Knowing that so many founders of modern computer programming played with radios, it would be interesting to speculate about how the ways of thinking from the realm of electromagnetism were transferred to modern software engineering.


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