If a dedicated server has VonCodecQuality=10 or lower the direct communication channel (DC) will be heard 3D (positional) around the player using the channel. Also the other channels will be heard 3D around the player to those players that are not in the specific channel (other group channel, vehicle, command etc. channel).

But if the server has VonCodecQuality=11 or higher it breaks the 3D function and the voice comms e.g. DC will no longer be broadcasted positionally but you just "hear voices in your head". (http://feedback.arma3.com/view.php?id=6894).

Also the broadcasting distance (and attenuation) changes for channels depending if 3D is working or not. When 3D works, DC can be heard to 80 meters with little attenuation but when the 3D is not working DC can be heard to 40 meters with no attenuation. Both these distances are too long but calls for another ticket. One exists for the case when 3D is not working: http://feedback.arma3.com/view.php?id=16723