How change freepbx audio codes?

,

i have two questions :

Question1-

about ““the audio codes of voice in freepbx””… is is controlled from freepbx?? or from the client voip side ?

i mean that if i have soft phone with code ulaw , and i have freepbx with specific audio code ,
which audio code will run ?

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Question2-
we have problem in low voice quality and interrupt when client has low speed internet .

my request is how to use the lowest voice quality that has the lowest bw and as a result we fix the problem of low quality and interrupt?

with my best regards

Did you read the wiki yet? It’s all there.