[ubuntu] Slow wireless connection

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http://ubuntuforums.org – I have problems with slow WiFi connection on my Lenovo notebook with Ubuntu 12.04. When I try to play MP3 or movie from my network / server connected to local network through WiFi, it plays really slow, buffer somehow. When I connect to network with cable, the speed is OK. WiFi signal is excellent. Can you help me with that? (Hardware)