A mistake would be clipping the beginning or ending of the audio. Carefully editing out the 911 dispatcher’s question about what color the perp was was a deliberate act. NBC is still lying.
Exactly. Moreover, if you listen to the dishonestly edited version of the audio, you can hear a distinct difference in the audio background. At the edit point, Zimmerman seems to have shifted the phone in his hand or something because you can hear the noise. In the original unedited version, the background sound seems normal and actually starts before he says that he thought that Martin was black. In the edited version, it begins suddenly at the edit point.
Not only was the edit dishonest, it was sloppily done.