[asterisk-dev] Request for User Configurable DTMF Twist settings to be in 1.8 and above.

[Alec Davis]

Review https://reviewboard.asterisk.org/r/2141/ are the changes proposed.
It adds 4 user adjustable twist variables to dsp.conf, defaulting to AT&T
values if left as is.

The issue is that the current Asterisk DTMF specifications are based on the
AT&T specs.

But we are seeing reports in non AT&T deployments that are not having a very
succesful DTMF hit rate.
By changing the values (removing the twist tests) in ASTERISK-20442 tbsky
(based in Taiwan) was able to get 100% hit rate on caller id. He'd already
set relaxdtmf in chan_dadhi.conf

For reference the table below shows the different acceptance values for
twist(normal/reverse).
 
; Power level difference between frequencies for different
Administrations/RPOAs
;              Power Gain               equiv
;              normal  reverse          dB's
; AT&T(default) 6.31    2.51            8dB(normal), 4dB(reverse)
; NTT           3.16    3.16            Max. 5dB
; Danish        3.98    3.98            Max. 6dB
; Australian    10.0    10.0            Max. 10dB
; Brazilian     7.94    7.94            Max. 9dB
; ETSI          3.98    3.98            Max. 6dB

The review only adds additional configuration options to a deployment, and
doesn't change any functionality, if left at defaults nothing changes.

Alec Davis