Interesting filming facts about Michael Manns 1995 movie ‘Heat’ starring Robert De Niro and Al Pacino;
1) “Principal photography for Heat lasted 107 days. All of the shooting was done on location, Mann deciding not to use a soundstage.”
It seems very strange that all filming was shot primarily on location – in most high budgeted films and TV shows are now predominantly filmed in a studios – it allows better quality of setting and audio. the fact that Mann decided to not use a sound stage probably really affected the quality of the audio recording – in Sound stage the walls are padded to absorb the best audio.
2) “All the gun sound effects in the shootout sequence were taken from onset audio”
The director had originally planned to add gunshots to the audio in post production. But when he tried to do so, he didnt feel like is sounded real enough, so he kept the audio as it is.