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Modem dial tones

By jardinier ·
Why do dial-up modems, both internal and external, make funny noises rather than a regular dial tone like a telephone?

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by willcomp In reply to Modem dial tones

Actually they sound rather like a phone when dialing. Like a re-dial on regular phone, it happens quickly.

The cacaphony you are probably referring to occurs when the other modem answers and handshaking between the two modems is happening. That process is quite noisy and takes longer for high speed modems. Essentially each modem is telling the other what speeds and protocols it can handle and they are verifying capabilities.


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by TheChas In reply to Modem dial tones


Listen very closely.

When the modem first connects to the line you will hear the dial tone for the short time it takes for the modem to verify that the line is active.

Next, comes the 7 or so tones for the phone number.

The cacophony you hear while the modem is negotiating the connection with the service is the Dual-Tone Multi-Frequency (DTMF) signals used for data communications over dial-up phone lines.

The dual tones make up the one's and zero's of the data.

The tones are loud in order to keep a high signal to noise ratio to improve data transfer accuracy.

This noise goes away after the connection is made because the default setting for most modems is to turn off the speaker after the connection is established.

The only reason to not turn the modem speaker all the way off is that with the speaker on, you know when your modem is dialing and can detect if a dialer worm had infected your system.


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