Phone Tones

Original artwork by  Michael Zhang .

Original artwork by Michael Zhang.

This episode was written and produced by Casey Emmerling.

We unpack how touch tone dialing changed communication forever. Join us on a deep, quirky dive into telephone history. We’ll also deconstruct these sounds and reveal their hidden brilliance. Featuring author Annabel Dodd and telephone aficionado Jim Hebbeln of the Telecommunications History Group.


Before the Lens by Steven Gutheinz
Soft Shoe by Steven Gutheinz
Friday Night 8pm by James Childs
Creature Set by Uncle Skeleton
Allright by Uncle Skeleton
Ode to Estes by Uncle Skeleton
All Coming Together by Dexter Britain
Retrofuture by Uncle Skeleton
Something to Believe In (Instrumental) by Benjamin Love
Sweethearts by Uncle Skeleton
Cherry (Instrumental) by Chair Model
Waiting on You (Instrumental) by Breakup
When You Come (Instrumental) by Kylie Odetta
You've Got Me Running In Circles (with Oohs & Ahhs - Instrumental) by Sonny Cleveland

20K is produced out of the studios of Defacto Sound and hosted by Dallas Taylor.

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View Transcript ▶︎

[SFX: Dial tone] + [SFX: Phone dialing] + [SFX: ringing]

Hello! You’re listening to Twenty Thousand Hertz. I’m Dallas Taylor.

[music start]

The sound of a number being dialed on a telephone is instantly recognizable. But now-a-days, how often do you really hear those sounds? When we call a friend, we just scroll down to their contact. When we call a business, we Google it, tap the phone number, and tap to call. Or we just ask our phone to call it for us.

[SFX: Siri Voice: Okay, calling Music Millennium]

Up until pretty recently every call you made meant dialing all 10 digits of a phone number, one button at a time. And that meant hearing those tones over and over. If there was a phone number you dialed a lot, like your best friend, or your parents, you’d eventually memorize what their number sounded like. Strung together, the tones would start sounding almost musical. Like a jingle you couldn’t forget even if you tried.

[SFX: Mario DTMF]

[music out]

But before we jump into the push button phones most of us are familiar with, we need to go back to the very beginning.

[music start]

There’s still some debate as to who exactly deserves credit for the invention of the telephone. But we do know know that Alexander Graham Bell was the first to patent it. That was back in 1876. A year later, Bell and his father-in-law formed the Bell Telephone Company. Over time, the Bell Company evolved into the American Telephone and Telegraph Company, or AT&T as we know it today.

[music out]

[SFX: AT&T Slogan: When you can hear the joy, that’s AT&T. Reach out and touch someone.]

A quick sidebar: The distinction between Bell and AT&T gets pretty convoluted, and you’ll hear them being used interchangeably throughout this episode.

Right away, it became clear that AT&T had a monopoly on the new telephone industry, meaning they could charge whatever they wanted for phone service. This was especially bad news for anyone who lived outside of the city, since it was expensive to run miles of phone line out to just a few houses. So, to convince regulators they should be allowed to operate, AT&T did the most obvious thing a major corporation could do! They struck a deal with the federal government.

[music in]

Annabel: AT&T would promise to provide phone service throughout all of the United States, Canada too…

That’s Annabel Dodd, a professor, consultant and author of The Essential Guide To Telecommunications.

Annabel: Then in return, AT&T would not only provide the phone service, but would provide universal service where people in rural areas weren't charged anything higher than people in urban areas, so that there was comparable prices throughout the United States.

With the signing of that deal, the era of the telephone had begun. Soon, telephone lines were installed all across the country. But, calling someone back then was very very different than we know it today.

[music out]

Annabel: The early years are very interesting. At the time in the early 1900s, late 1800s, United States was largely agrarian, rural country. People had phone service, but they didn't have a dial on the phone. They'd pick up the handset and reach the operator and they would direct the call to whomever that person requested. And that telephone operator knew everything that was going on in the town. And who was talking to whom.

As you might imagine, being the gatekeeper for every phone call made in your town gave these operators quite a bit of power.

Jim: In Kansas City there was an undertaker, his name last name was Strowger, S-T-R-O-W-G-E-R.

That’s Jim Hebbeln. He worked in the telephone industry for over 40 years, and now volunteers with the Telecommunications History Group.

Jim: And he was wondering why he wasn't getting as much business as his competitor, until he realized that his competitor’s wife was the switchboard operator in Kansas City, and so if someone asks for an undertaker, his competitor got the business.

Strowger realized that if people could call each other directly, without an operator, he could stop his rival from stealing his business. So, using a hatbox and some mechanical equipment, he designed what would become known as the Strowger Switch.

[music in]

Jim: It didn't have a dial at the time, initially you might have three buttons on your phone. You'd pick up the phone and one button would be labeled hundreds, another one would be labeled tens and another one would be labeled units, and if you were supposed to dial 1-5-3 you'd press the hundreds button once, [SFX] and it would cause the switch in the central office to jump up one level and connect to another switch. Then you'd press the hundreds key five times, click, click, click, click, click, and it would go up five and then you press it the units digit three times. Click, click, click and it go over three and it would ring their phone [SFX].

The Strowger Switch was eventually replaced by the type of phone we all know from old movies, the rotary dial phone.

[music out]

To dial a number on a rotary phone, you put your finger in the corresponding slot, spin it clockwise all the way to the right [SFX], then pull your finger out while the dial spins back into place.

[SFX: Rotary Dial Ad: For example, suppose you want to dial 23650. Dial each numeral in this manner, pulling the dial around to the finger stop each time. Be sure to allow the dial to freely return to its normal position.]

Annabel: So those phone calls, took I think it was 11 seconds to complete dialing. And the problem with that was that the dialing tied up phone company equipment for a long time. The phone company couldn't handle as much traffic as they wanted to.

[music in]

To speed up long-distance calling, which still required an operator, the phone company developed a new switching machine called the Number Four Crossbar. This was the first time a keypad of numeric buttons was widely adopted, though it was only available to operators.

Jim: The operators had a key pulse, it's a dial, but digits were arranged in two columns of five digits per column, and they could just tap on these buttons and it would produce a pair of tones for each digit dialed.

Since each number on the dial used a specific pair of pitches, the sounds they produced were called “multi frequency” tones, or “MF” tones.

[music out]

Jim: The tones were 700 [SFX], 900 [SFX], 1,100 [SFX], 1,300 [SFX], 1,500 [SFX] and 1,700 [SFX] hertz, and some combination of two of those tones would represent each digit. For example, 700 and 900 was a one [SFX: MF 1], 700 and 1100 was a two [SFX: MF 2], 900 and 1100 was a three [SFX: MF 3].

The Bell System saw the benefits of a touchpad right away.

Jim: People within the Bell System watch these operators just be able to go [SFX] push, push, push, push, push, push, push, push and dial these numbers rapidly in a couple of seconds rather than using a rotary dial.

Bell wanted to get push-button phones into the hands of customers, but the oscillators that made these MF tones were too expensive to mass produce. In 1948, in the suburb of Media, Pennsylvania, Bell made a handful of these push-button, keypad telephones and gave them to customers to try out.

Jim: They had six different length reeds that were tuned and you could push the buttons, one, two, three, four, five on the phone, but it would produce multiple frequency tones like the operators did by plucking two of the six reads, [SFX: Kalimba plucking] bing, bing, bing bing.

[music in]

Customers immediately loved the convenience of dialing with a touchpad. Unfortunately, the reeds weren’t sturdy enough to stay in tune after repeated use, and the prototype was shelved. Though in the 1950s, Bell experimented with different phone designs, and eventually settled on using transistors to produce the tones for each key. They still hadn’t decided on the best layout for the buttons, so they brought in a group of volunteers to test different button arrangements.

Jim: And in the process of doing human studies, they decided that the best kind of a dial was something similar to like what accountants used on adding machines, but the public didn't like the dial starting from the bottom and going up like adding machines did. They wanted their digits displayed across the dial like you read off of page of paper: one [SFX], two [SFX], three [SFX] across the top, seven [SFX], eight [SFX], nine [SFX] across the bottom. Accountants did not like Touch Tone dials, but everybody else enjoyed the design.

[music out]

Arranging the buttons in a grid allowed Bell to assign a pitch to each column and a pitch to each row. Each button pressed would simultaneously produce the tone from its column [SFX: tone] , and the tone from its row [SFX: tone] . These were called “Dual Tone Multi Frequency” or “DTMF” tones. AT&T patented it with a catchier name, “Touch Tone.”

[SFX: World's Fair: Hi, this is the Bell System’s new Touch Tone dialing. With this indicator, you see how many seconds you save the new way. Let’s try it! Okay, I’ll race ya. Ready, go… I beat ya.]

[music in]

Although DTMF shares many similarities with MF tones, there are important differences. For one thing, they use a completely different set of pitches.

Jim: So in the process of figuring out what tones they wanted to use, they picked some really odd tones that don't really match up with any tuned musical instrument, they're always off key. So they picked these bizarre frequencies like 697 hertz [SFX] or 852 hertz [SFX] for the different pitch tones.

And unlike MF tones, which are only dialed at the beginning of a call, DTMF tone-receivers are ready to receive a key input at time during the call. By choosing these odd, specific frequencies, Bell made sure that nothing else, from music [SFX: distant music] to traffic [SFX: cars] to human voices [SFX: Voices] could be misinterpreted as a key press.

Here are the numbers one through nine on a Touch Tone phone. See if you can hear the two separate pitches for each button.

[SFX: Dialing 1-9]

If you listen closely, you can hear how the row pitch, (which is lower) changes after every third button, while the same pattern of three pitches (for the columns) repeats on top of it.

[SFX: Dialing 1-9]

Since the bottom row of keys had two extra slots, Bell added the pound and star keys. These buttons really didn’t have an intended use early on, but later gained more functions. Things like dialing *69 to find out the last number that had called you or star 67 to prevent the person you’re calling to see your number on their caller ID.

[music in]

Touch Tone technology would go on to dominate the second half of the 20th century. But, it wasn’t without a few hitches. After the break, we’ll hear how people learned to “hack” the Touch Tone system, and how these tones might be disappearing from our society altogether.

[music end]


[music in]

Early versions of the telephone led to AT&T’s patented “Touch Tone” technology. The phone company loved it because it tied up their switching equipment for far less time than rotary phones did. Customers loved it because, well, it was more convenient.

Here’s a commercial by C&P Telephone, an East Coast branch of Bell.

[music out]

[SFX: Touch Tone Ad - It’s a lot easier. And if you have to have to make a lot of calls, like we do here in this office, it’s just great to have. Where with a Touch Tone, you’re dialing a number as fast as you’re thinking it. You’re thinking, uh, 411 for an operator, where with a dial phone it’s 4… 1… 1… My parents had dial service for years and years and years. It took me like a year to talk them into getting Touch Tone, and now they wouldn’t give it up.]

[music start]

This Touch Tone technology quickly swept the globe, and businesses developed automated answering systems that you and I know and love. It took advantage of this new DTMF technology.

Annabel: It became a way for entry into data systems. So the automated attendants, “Press one if you want to reach sales, press two if you want customer service, press three if you want to hold for three hours for an operator.” You know most people hated it.

[SFX - Answering system - “Your call is important to us… Please hold”]

It may not surprise you to hear that pre-recorded phone menus weren’t exactly popular, but there were some benefits. For example, you could enter in sensitive information like your bank account number or social security number without having to say the numbers out loud. Now, that doesn’t mean someone listening in can’t decode them, but that’s another story. Another important use of these tones was voicemail control.

[SFX: Voicemail: You have three saved voice messages. To listen to your messages, press one.]

Annabel: Voice messaging was a big application for Touch Tone.

While answering machines that recorded onto tape had been around since the 1940s, the voicemail services that came out in the early 80s began storing messages digitally, and relied on DTMF tones to control functions like restart, skip, and delete.

The explosion of voicemail machines also led to a bizarre trend of using kitschy, pre-recorded songs for voice messages. In the early 80’s, a company called Formidable Inc. sold a tape of “Tele-Tunes” with 13 different messages that people could put on their answering machines.

[SFX: Song 1: Talk to this machine. Leave a message that you mean. If you leave your name, and where you’re at, I’ll call you right back!]

[SFX: Song 2: We’re not in, but you can leave a message at the tone. We’re not in, we’ll be back soon. We’re not in…]

[SFX: Song 3: So when you hear that little sound you can start to speak, but don’t hang up when you hear the beep. I’m in the shower, can I call you back? I’m in the shower, can I call you back?]

DTMF also had applications beyond the telephone. For instance, DTMF tones were used by TV networks to insert local commercials into national broadcasts.

Jim: They were using touch tones to tell a local controller that they were able to then insert their local commercial for the next 30 seconds.

So, let’s say it’s 1988. You’re watching a new sitcom called Full House, on ABC. The show cuts to commercial.

[SFX: ABC Messages: After these messages, we’ll be right back.]

First, you see some ads for big, international brands:

[SFX: RC Cola Ad: Nothing really gets to you like RC Cola can.]

[SFX: Atari Ad: The fun is back, oh yessiree, new 2600 games from Atari.]

[SFX: Die Hard Trailer: Bruce Willis. Die Hard. Got invited to the Christmas party by mistake. Who knew.]

These ads are visible to everyone watching the show, no matter where they are. But then you see an ad specific to your area: maybe it’s for a local furniture store...

[SFX: Harlem Furniture Ad: Harlem furniture, you'll like our style…]

A DTMF signal transmitted by ABC tells the affiliate station when to insert these local ads, and when to cut back the main broadcast. In fact, before the technology improved, you could actually hear these tones during the commercial break. Here’s a less than subtle example on A&E.

[SFX: A&E DTMF: You're watching the A&E Cable Network, the best in comedy, drama, documentary and the performing arts.]

And here’s one from Nickelodeon.

[SFX: Nickelodeon DTMF: Ready or not, fellow mutants, I'm back with more freaky facts on Nick's Kid Almanac.]

[music start]

No discussion of phone tones would be complete without mentioning the Phreaks (that’s Phreak with a “P H”). It’s important to remember that even after phones started using DTMF to communicate with switching equipment, calls were still connected using those original MF tones. In the 60s, a group of college students figured out how to manipulate the receiving machines by producing these tones artificially.

Jim: Most of them were just discovering how the system worked. They were curious, they were not out to make money, they were not out to fraudulently sell free phone calls to their friends for a whole lot less than what the phone company would charge.

[music end]

The key to hacking the phone system was reproducing a tone of 2,600 hertz.

[SFX: 2600 hertz tone]

Jim: It's around E or E flat, a couple octaves above middle C. I used to be able to whistle it, but I can't anymore, which used to really irritate people, cause if I'd walk in a room and whistle it and if they were on a long distance call, it would knock their call down.

By producing a tone of 2,600 hertz, the Phreaks could trick a remote switching machine into thinking the call had been disconnected. From there, they could make long distance phone calls and disguise them as a call to a toll-free number or directory assistance.

Jim: So you had a little box that would manufacture the multi frequency tones and you just punch in deet deet deet deet deet deet deet deet deet [SFX] and the other end just blindly put the call through, no questions asked…

Famously, the Phreaks often used plastic toy whistles that came in boxes of Captain Crunch cereal in the 70s. If you glued a hole on the whistle shut, the whistle would consistently produce a tone at 2,600 hertz [SFX].

Jim: I have to admit, I did it a couple of times using a Hammond organ to simulate the MF tone. It did work. I was satisfied that it did work, but I didn't want to get in trouble because I didn't want to jeopardize my job.

[music in]

Like everything else, the phone industry was changed dramatically by computers. In the 90’s, the phone system started to turn digital, and multi-frequency tones lost many of their original functions.

So, in other words…

Jim: No more phone Phreaking [laughs].

Unfortunately, these technological advancements didn’t translate to higher quality calls. You’ve probably noticed that phone calls still sound pretty terrible. This is because of data compression. To push all of this data, they reduce the audio quality as much as they possibly can. (whispers) Way too much in my opinion.

First, they chop off all of the low frequencies [SFX]. This one kind of makes sense because most of us take calls on tiny speakers. Those tiny speakers can’t make those frequencies anyway. But then, they chop off even more of the low frequencies [SFX]. Ok, well, we can deal with that… but THEN, then chop off some of the high frequencies [SFX]. Ugh, I’m starting to sound pretty terrible. Then the audio gets hyper compressed, meaning it kind of just brick walls and slams all of the audio at a single volume. To top it all off, the audio data gets hyper compressed as well [SFX]. So, here’s where we land. Bla bla bla, yuck yuck yuck, gross gross gross.

Jim: So there's a definite trade off between cost and quality.

[music out]

For most of us, oh hold on one sec… [SFX: switching back to high quality audio]

For most of us, the convenience of a cell phone is worth the tradeoff. As for those Touch Tone sounds, they’re really there just for show.

Jim: It's just a digital packet. Your phone produces Touch Tones only to be able to do end to end signaling, like operating voicemail systems or automated attendants that answer at the far end.

[music in]

But even those uses are becoming outdated. Between text, email, and social media, we don’t leave voicemails anymore. When we do need to check our messages, we can do so through an app, no phone call required. As for automated attendants that use Touch Tone sounds, those are gradually being replaced with voice recognition.

[SFX - Robo voicemail - “You can say 'Billing question,' 'update address,' or 'Speak to a representative."]

It’s very possible that within the next decade or so, Touch Tone signaling will be a thing of the past. Once it is, will phone companies even bother to put these useless noises onto our cell phones? Will the next generation even recognize those sounds? I mean, when was the last time you heard this [SFX: Ready dial tone sound] or this [SFX: Phone off the hook sound].

Just like those other phone sounds, touch tone sounds might slowly fade into oblivion. Before you even realize it. Whatever happens in the future, it’s undeniable that Touch Tone had a huge impact on not only the telephone industry, but mass communication in general… and those of us who grew up hearing DTMF tones on every phone call we made will never forget what they sounded like.

[music end]

[music in]


Twenty Thousand Hertz is produced out of the studios of Defacto Sound, a sound design team dedicated to making television, film and games sound insanely cool. Find out more at defactosound.com.

This episode was written and produced by Casey Emmerling, and me, Dallas Taylor, with help from Sam Schneble. It was edited, sound designed and mixed by Jai Berger and Colin DeVarney. Special thanks to our guests Annabel Dodd and Jim Hebbeln for taking the time to speak with us.

Jim, last question, so out of all of the sounds in the world, what is your favorite sound?

Jim: It probably would be those multi frequency tones. Well, just a second, I probably would say that comes second, I love you… You know, from my wife.

To learn more about the Telecommunications History Group, the group that Jim volunteers with, go to telecomhistory.org, or check out their museums in Seattle and Denver. And, check out Annabel’s book, The Essential Guide to Telecommunications.

The music you heard throughout this episode came from our good friends at Musicbed. Check them out at Musicbed.com

What’s your most memorable telephone story? We’d love to hear from you, and you can get in touch on Twitter, Facebook, or by writing hi@20k.org.

Thanks for listening.

[music end]

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