1. Issue: Windows 10 Version 1903 and 1909 TAPI Incompatibility

Date of issue reported June 12, 2019, 

TAPI is Microsoft’s Telephony API which we leverage to make Voice calls over TAPI compliant modems. The latest release of Windows 10 has broken audio for these calls. After updating Windows 10 to version 1903, users are experiencing no audio playback during phone calls made with a TAPI modem. 

This issue was created by Microsoft Windows and any devices that support TAPI (including WIN-911) were impacted by the update. 

A. Affected Systems


This issue impacts both WIN-911 V7 and WIN-911 Standard, Interactive or Advanced users. However, this only applies if you are using TAPI modems for Voice notifications.  

If you use a Multi-Tech MT9234MU-CDC-XR modem for Voice notifications, your system will be impacted. Other TAPI compliant modems are likely affected as well.

WIN-911 systems using Dialogic boards or VoIP for Voice notifications are NOT affected.


B. Recommended Actions

The compatibility of Windows 10 Version 1903 is a Windows issue and outside of the control of WIN-911. However, as WIN-911 is investigating a workaround the current solution is to disable Automatic Windows Updates to prevent an upgrade to Windows 10 version 1903.

If your Windows installation previously updated to version 1903 and you're using a TAPI modem, we recommend downgrading to version 1809 and disabling Automatic Windows Updates.

WIN-911 Software works with previous versions of Windows 10 Including:  

  • Version 1809 (OS build 17763)
  • Version 1803 (OS build 17134)
  • Version 1709 (OS build 16299)
  • Version 1703 (OS build 15063)
  • Version 1607 (OS build 14393)

If you require assistance downgrading Windows 10 the following steps will walk you through the process.

C. Alternative Solution to TAPI 

Since this issue is outside of the control of WIN-911 the recommend alternative to TAPI is to use the Grandstream IP PBX. The Grandstream Overview Video will discuss the product and the Grandstream Configuration article will walk through the configuration. 

Note: Grandstream requires WIN-911 Version 3.19.9 or higher and is only available on the Interactive or Advanced license. Grandstream does not work with Version 7.

If you are not interested in using the Grandstream to future-proof your voice solution, then as a temporary fix, you can revert back to the previous version of the operating system. If the Windows update has happened within the past 9 days, you can follow these steps, but after 10 days, Windows will not let you roll back.

There is also a registry edit process that can successfully get the TAPI modem working again in the versions that broke it. 


Procedure to fix Windows registry:

Open Windows registry for edit - (Click start button, and type "regedit")

1) Goto [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Drivers32]

Find the last wave parameter; say for example "wave" and "wave1" already exist, you would need to create a new wave entry that is 1 number higher than the existing entries: wave(+1):


(if you only have "wave" you would create "wave1", if "wave" and "wave1" and "wave2" already exist, you would create "wave3") 

2) Goto [HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Windows NT\CurrentVersion\Drivers32]

Add the same as in (1)


3) Restart the computer

2. Downgrading Windows

1. Click Start, then Settings:

2. Click on Update & Security: 

3. In the sidebar, choose Recovery:

4. Under Go back to the previous version of Windows 10 click Get Started:

5. Select why you’d like to go back to a previous build and click Next. If the link is greyed out, you did not select a reason from the checkboxes above.

Technical support

To create a support case, you will need either your Maintenance Support number or your CD Tracking number. You can create a Case online or contact the product support line: (512)326-1011.