AMI Monitor action not working correctly

Hi guys.
I am using the asterisk manager to record calls on my asterisk 1.6.2.14. The action on the manager interface goes like this:

Action: Monitor
Channel:
Mix: true

This is executed with success and the recording starts on the specified channel and the bridged channel as well. When the call ends asterisk puts the two wav-files into one and here the problem occurs. The wav-file consists of first the voice from one channel and then the voice from the bridged channel. They should be mixed together, not player after each other. If I set Mix: false the result is exactly the same. I have done this many times in Asterisk 1.4 without issues. What can be wrong here?

“Mix: 1” is the same.

Thanks

Resolved: The included sox version 12.18.1-1 in AsteriskNOW does not support the -m (mix) flag. I downloaded SoX v14.3.1 and compiled and installed it from source. Then it worked.