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Home Technical What's a Voice Modem?

What is a Voice Modem? (Updated 27-Mar-06)

Most modems can be classified with these characteristics:

  • Data/fax
  • Data/fax/voice
  • Data/fax/voice/speakerphone

Voice generally means that the modem is capable, with appropriate software, of supporting telephone answering machine functions: the modem can 'record' and 'play' to the Windows wave device. The answering machine software will also use the sound card on the machine to play and record. The software may also include functions to dial or answer calls using your sound card's microphone and speakers or headphones.

Windows comes with a Phone Dialer. This utility will dial a number with any type of modem; after Phone Dialer dials a number, you use any normal phone (connected to the 'Phone' jack of the modem) to complete a voice call.

Third-party software can be used with a voice modem to enhance functionality. One such package: ModemSpy can record phone calls to wav files.

All modems are also capable of supporting voice functions provided by 'Internet Telephony' - the modem is connected to your ISP in data mode, and software on your system sends and receives voice-encoded data to a compatible telephony server to complete a call. (Many of these services used to be free.) Some providers include: PhoneFree, Dialpad, IConnectHere, Net2Phone, and Skype.

A modem that includes speakerphone capability will have additional audio components on the modem to provide an interface for a microphone and speaker or headset. This allows the modem to dial or answer and provide high-quality full-duplex voice functionality.

Full duplex means you can talk and hear at the same time. Many 'voice' modems when used on voice calls will provide only half-duplex functionality: at any instant, you can either be talking or listening. The quality of the audio produced using a voice modem is often a problem.

Voice modem chipset makers include in the driver or firmware code to interface to the wave device, but do not develop the software that provides voice functionality. The modem makers generally bundle  "compatible" third-party voice modem software. Some voice modem software offerings: Ring Central, BVRP, and Messaging Software. Microsoft Windows provides TAPI (a telephony application program interface) and a Unimodem service provider (driver). The Microsoft-provided Unimodem driver uses your modem driver (.inf file) to support TAPI-compliant applications and your modem. 

CALLER ID is not automatically supported by all modems. In most cases, data/fax modems will not provide any caller id support. The chipsets for voice, speakerphone and even most data/fax modems are capable of caller id, but the modem must include additional components: the caller id signal is sent by the phone company between the first and second rings while the phone, or modem is still on-hook. Modems that support caller id must have a circuit to receive the caller id information without taking the modem off-hook. 

DISTINCTIVE RING - Many modems are capable of supporting distinctive ring - however, Windows XP & 2000's Microsoft-provided Unimodem is not: see Distinctive Ring & Modems.


I can hear but they can't hear me: If you are using a microphone connected to your sound card, make sure that the microphone is enabled in Windows (volume control /mixer). To do this: double-click the Volume icon in your taskbar. (If you can't find it there, you can also access it from Control Panel -> Sounds - Audio tab - Volume... button. Switch to Recording properties by clicking 'Options' on the Volume Control's menu, then Properties:

Make sure Microphone is checked, click OK, and then adjust the mixer control for the microphone all the way up. On the playback properties, be sure and select 'Phone' and adjust the slider for it as well (to hear).

If you still can't hear or be heard, you may not be using compatible software, or your modem is not capable of interfacing with your software. (For example, Microsoft Windows phone dialer software will not permit soundcard/mic input - it can only dial phone numbers.)

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