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Unimodem Modem Audio sound driver missing in Windows 10

Microsoft Windows 10 Version 1511 (Build 10586 and later) have a Unimodem problem that prevents voice modems from installing the Unimodem Full Duplex or Half Duplex Audio Driver.  This prevents some TAPI Voice applications from properly detecting the modem as a voice modem, and/or prevent the modem from playing back any audio to the modem. The exception is voice software that uses TAPI ‘passthrough’ mode to communicate directly to the modem.  If you are using a Conexant based voice modem please see additional notes below.

PROBLEM: If you updated from an earlier version of Microsoft Windows including Microsoft Windows 7, Microsoft Windows 8.x or Microsoft Windows 10 version 1507 (build 10240) to Microsoft Windows 10 version 1511 (builds 10586) or later, the Unimodem Full Duplex or Unimodem Half Duplex Audio driver for your ‘dialup’ fax/voice modem may no longer be installed in Windows.

SOLUTION: This problem was corrected by Microsoft in an Windows Update. Microsoft Windows 10 Version 1607 (Builds 14393.479 and later include this fix to Modem.sys for both 32-bit and 64-bit Windows)

You can verify your version of Windows 10 by right-clicking Windows Start, Click Run, and type ‘WinVer’ (Or Windows Key+R and type WinVer and press Enter) also, you can check the properties of the Modem.sys file in your Windows\System32\Drivers folder. The properties should report version 10.14383.479 or later.

NOTE: Windows 10 version 1903 and 1909 also introduced a new problem with voice modems. Please see this document

Conexant based modem considerations

If you use a Conexant based voice modem, some USB models will not be detected by Windows 10 as Voice compatible when using the default drivers. The default Windows drivers will usually install these modems as a Conexant CX93010 ACF Fax Modem. (Some of these modems have been identified with a PID of 1329, 1340, and 1349) This driver is sufficient for faxing and data, but will not provide voice compatibility with TAPI compliant voice software. The Unimodem Full Duplex or Half Duplex Audio driver is not installed as this modem is not detected as a voice modem.

Some specific USB models of Conexant voice modems (identified as PID 1329,1349) can be updated using Windows Update. The update will replace the existing Conexant CX93010 ACF Fax Modem driver and install a driver named USB Data Fax Voice Modem. This driver is detected as voice compatible, so Windows will also install the Unimodem Half Duplex audio driver with the corrected Windows 10 update.

To add to the confusion, an outstanding bug in the Windows Unimodem Tranform Module DLL (umdmxfrm.dll) prevents any audio to be played back with all these type of Conexant modems regardless of the modem driver you use above. The exception is TAPI compliant voice software that communicates directly to the modem using TAPI ‘passthrough’ mode. FaxTalk Messenger Pro will operate correctly with either driver listed above, with or without the Unimodem Audio driver installed.

The Conexant Fax Modem includes a custom driver to correct the issues with software using TAPI, so the modem will provide audio playback and recording with your TAPI or TAPI passthrough software. If you are looking to replace your modem and cannot find a compatible “voice” model we recommend this hardware based Conexant Fax Modem.

Unimodem Audio Driver Missing
Unimodem Audio Driver Missing

Further discussion

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We tested the voice and fax functionality with FaxTalk FaxCenter Pro, FaxTalk Messenger Pro and FaxTalk Multiline Server.  All voice mail functionality is working normally without the presence of the Unimodem Audio Driver in Windows 10 version 1511 or later. Call screening and playback for incoming calls in voice mode is working.  We have verified with Conexant USB Modems, MultiTech Modems using LSI/Agere chipset, and LSI 2.0 Chipsets.

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