Voice Support via TAPI Modem driver

Most of existing Voice-Fax programs designed to operate with Voice Modems, does not really use TAPI to work with voice functions. Even when working via modem driver, the so-called passthrough mode is generally used. In the passthrough mode the program communicates with the modem directly, the implementation of voice commands in the modem driver is not required. However, some programs work with Voice Modems via TAPI functions, that requires a full Voice Modem Support in accordance with TAPI specification. Examples of such programs are CallStation and IVM Answering Attendant Software.

Fax Voip T.38 Modem program is equipped with TAPI compliant Fax Voip 14.4K TAPI Voice-Fax Modem driver. With this driver voice modem functions are supported not only in the passthrough mode, but also via standard TAPI functions. The standard Unimodem Full-Duplex Audio Device driver is automatically installed by Windows when installing modem driver.

When operating using Fax Voip 14.4K TAPI Voice-Fax Modem driver via TAPI and passthrough mode is disabled, the 8-bit unsigned linear PCM at 8000 Hz format is always used.

The installation of Fax Voip 14.4K TAPI Voice-Fax Modem driver also fixes the well-known playback bug with Unimodem Transform Module in Windows Vista and above (include Windows 11 and Windows 10, both x64 and 32-bit) which prevents from playing audio through the modem to the phone line. Any telephony application that uses the modem wave driver to play audio through the modem will encounter this problem. This problem is debated for many years on Microsoft forums, but for some reasons has not been solved by Microsoft so far.

Also, in Fax Voip T.38 Modem the Hardware Hangup by detecting CD dropping from lowering DTR signal feature is implemented. This is often used by TAPI applications to reset the modem.