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Why did dial-up modems make so much noise?



  A whooping cartoon of a dial-up modem
Benj Edwards

Screeeech. . . to be. . . squaawk. These are familiar sounds to anyone who has ever used dial-up internet or called BBSes. It seemed noisy especially late at night. Have you ever wondered why all that sound was needed? And did you know that you could have muffled your noisy modem?

Wait, what is a modem?

In the past, people had to use a peripheral device, called a dial-up modem, to connect to online services or to link two external devices to computers. Dial-up modems are designed to work with the regular wired telephone network that connects almost every home and business in the developed world.

Using special software, your computer would give your modem the telephone number to be called. Your modem will then connect to another modem (and computer) on the other side of the line. The two computers could then share data, such as files or messages.

The word "modem" is a combination of "modulate" and "demodulate". Modems record and convert (modulate) digital data into audio frequencies that can be transmitted over the analog voice telephone network. The modem on the other end of the line receives those sounds and converts (demodulates) them back into binary data that a computer can understand.

A similar principle was used to store digital data on analog compact audio cassettes during the early PC era home of the 1

970s and 80s.

Why the Screeches?

If you interrupt a modem connection by picking up a telephone receiver and listening, you will hear screeching, hissing, buzzing and various other sounds.

"That's the actual sound of the data being sent and received," said Dale Heatherington, co-founder of Hayes Microcomputer Products and the circuit designer of the first direct-connect modem with a speaker.

Specifically, the sounds you hear at the beginning of a modem connection the two modems "handshaking". Handshaking is the process of two modems testing the waters and negotiating settings, such as which speed and compression methods to use.

This detailed chart, created by programmer Oona Räisänen in 2012, breaks down all the sounds you hear while handshaking

But wait a minute, why are we listening to modems performing this intimate dance in the first place?

Why did modems even have speakers?

  An Anderson-Jacobson acoustic modem link.
A modem with an acoustic coupling. Anderson-Jacobson

Before 1984, the US telephone network was a monopoly controlled by AT&T. The company had strict rules about who could connect a device to its network. To get around this, the first dial-up modems used devices called acoustic couplings. This allowed modems to be linked to the network acoustically, but not electronically.

To control a modem with an acoustic link, picked up the phone, dialed a number, and listened for a modem or person answering on the other side. When everything was clear, you put the receiver in two cups that served as a microphone and speaker. The connection would then begin.

After the new FCC rules eased the limitations of AT&T in the mid-1970s, companies began making direct-connect modems that were connected directly to the telephone system using modular plugs.

However, if a direct-connect modem dialed out and could not connect, there was no telephone receiver to let you know what was going on. A line may be busy or the call has been lost, an answering machine may be recording, or you may reach a fax machine instead.

To solve this problem, Hayes Microcomputer Products included an internal speaker in its groundbreaking 1981 modem for personal computers, the Hayes Stack Smartmodem 300.

  A 1982 ad for the Hayes Stack Smartmodem 300. [19659024] Hayes Microcomputer Products </span></figcaption></figure>
<p>  Heatherington designed the circuitry and firmware of the Smartmodem 300 and maintains a beautiful website with old photos of his time at Hayes. We asked him by email why he included a speaker in his modem design. </p>
<p>  "So that the user would know if the line was busy, a person answered or a modem answered," he replied. </p>
<p>  Certainly, an early print ad for the Smartmodem 300 emphasizes exactly these benefits of the modem's speaker, including monitoring the handshake process: </p><div><script async src=

Built-in audio monitor. Thanks to an internal speaker, you really listen to your connection. You immediately know if the line is busy or if you have reached the wrong number – and you don't even need a phone!

"As I remember there was some resistance to the idea because of the cost," said Heatherington. "But the benefits were worth it."

Hayes pioneered many technologies used in dial-up consumer modems in the 1970s and 80s. Features of Hayes modems, including the internal speakers, have been widely copied among competitors.

Since then, almost every built-in dial-up modem has had an option for audio feedback from the connection process You can thank Heatherington for the nostalgia of your 90s dial-up modem.

How to turn off the scream

It is no coincidence that the first modem with built-in speaker – the Smartmodem 300 – also first was you to turn that speaker off You did it with special codes called the Hayes Command Set which allowed people to change modem settings through simple commands using a AT prefix sent via terminal software.

To disable the speaker, simply send the serial command AT M0 before calling. (Put it in the initialization string of your modem.) You can also adjust the speaker volume with commands such as AT L1 . Here is a page from 1992 Hayes Modem Technical Reference that explains everything.

  A page from 1992
Hayes Microcomputer Products

In semi-modern versions of Windows, you can disable modem connection sounds in "Phone and Modem Options" in Control Panel. Internal modems on Mac OS X or higher can easily mute the system volume.

Anyway, if you use a dial-up modem nowadays, why not bask in the modulated tones of history? [19659039]! function (f, b, e, v, n, t, s)
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