[Asterisk-Dev] zaptel "rest value" of 0xff is not appropriate when ALAW is in use

[steve at daviesfam.org]

Hi,

I've just been doing some experiments on my test box with looped E1 PRI 
spans - playing with app_test with a view to adding more tests.

In the process I "Monitor"ed to disk the audio heard on both ends of my 
bridged call.

When I loaded the audio into Audacity to take a look, I was suprised to 
see that a channel that isn't being transmitted on seems to be seen at the 
receiving end as non-zero samples.  So every time the sending box starts 
and stops sending audio then there is a jump of the "zero level" to true-0 
and then back to the resting value.

The "resting value" is 832, which I note is AST_ALAW(255)

By contrast, AST_ULAW(255) is 0.

od -x </dev/zap/1 shows that channels not otherwise in use  receive 
nonstop 0xff.

So for channels that are being used for alaw, the "rest value" shouldn't 
be 0xff but rather 0xd5, being AST_LIN2A(0).

Steve