Why do faxes/modems produce strange noises ?

[McCrunchy]

And is the UFO-type squeak necessary for it to work properly ?

 

McCrunchy

[insane_alien]

i'm sure you've noticed that phones are used to transmit sounds. and that faxes and modems use phonelines to communicate.

 

so when you accidentally(or intentionally) dial a modem or fax number, you'll hear all the screeches and tones as the fax or modem tries to identify what type of modem or fax you are and if you'll allow it to connect to you.

 

as humans tend not to conform to the fax and modem communication standards you hear wild screeching. a fax or modem would screech back in a similarly bewildering manner and make a connection.

 

the screeching is the way they send data. it is actually the modem jumping between two tones. a high and a low. the data is encoded in the jumps between frequencies. for example, the jump from low to high could be a one and the jump from high to low would be a zero.

 

as the modem changes about really rapidly to send a practical amount of data per second, you hear a whole low of different tones rather than just high and low.

[CaptainPanic]

But why does a fax or a modem have a speaker?

 

Many faxes and (dial-up) modems actually make the screeching noise even when you use it properly.

 

I mean, while the signal is in the phone line, it's just some electrons (current & voltage). Why convert it into sound at all?

[insane_alien]

they do? mine never done that. and i just tried the modem in my laptop, it doesn't do that either.

 

i thought he just meant when you pick up a phone when it is connected to a modem and listen in.

[Mokele]

I've encountered fax machines with speakers. I assume it's so that you can hear what the machine is doing, and so you have some sort of audible assurance that it did make the connection correctly.

[John Cuthber]

I always thought it was to let you know when someone telephoned your fax/ modem line.

[bascule]

The noises you are hearing are quadrature amplitude modulation, which is where modems derive their name from (they are modulator/demodulators)

[CaptainPanic]

they do? mine never done that. and i just tried the modem in my laptop, it doesn't do that either.

 

i thought he just meant when you pick up a phone when it is connected to a modem and listen in.

 

In fact, modern fax/modems almost never make noise anymore. But I remember my first old dail-up modem. I am exaggerating when I say that I needed ear plugs.