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Biamp Systems

Changing the Hook Flash duration on an analog telephone interface

One of the many features our telephone interface supports is Hook Flash.  If your phone system supports it, a Hook Flash can put a line on hold, establish a second call, and then join them together. Occasionally, the Hook Flash doesn’t seem to work reliably with some phone systems. The reason is usually simple and easy to solve. 

Hook Flash mechanics

A Hook Flash is nothing more than hanging up and picking up the line very quickly. By default, Biamp's telephone interfaces are set to do a Hook Flash in 150 milliseconds. In some instances, this is too quick for the phone system to detect, so you’ll hear a click but the line will not go on hold and you will not get the second dial tone.  Extending the duration of the Hook Flash is usually the fix for this problem.

Changing hook flash duration

  • Locate the Control/Status block for your analog telephone interface in your file and select it. If you don't have a Control/Status block, check the How to restore the Telephone Control/Status block article.
  • Open the Property Sheet of the Control/Status block (right-click on the Control/Status block and select Properties).
  • Under the "DSP Attributes" tab, look for the "Hook Flash Duration" line.​

​​Hook Flash Duration.GIF

  • Increase the Hook Flash Duration to 300.
  • Reload your configuration file and test the Hook Flash.
  • If the Hook Flash still doesn't work, repeat this process of increasing the Hook Flash Duration by 50-150ms intervals.  If you get to a point where the hook flash hangs up on the first call, then the Hook Flash Duration is too long.
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