Codec vs Bandwitdh

In asterisk config files, the bandwidth variable could be set to low, medium, or high.

I would like nice quality audio, and I have Comcast Cable 8mbit download, 768Kbps upload, so which setting should I set it to? low, medium, or high?

Also there may be 20 concurrent connections so I would need the bandwidth to be able to support all of them.

Thanks for your help.

If you want to know what will be the bandwith
go to:

as for the qulity try G.711 then G.729 (you need license to use it)/ GSM (depends where you will connect no all providers have GSM)