From Halopedia, the Halo wiki
Album:
Halo: Combat Evolved Anniversary: Original Soundtrack
Composer(s):
Martin O'Donnell and Michael Salvatori
Length:
1:21
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In The Substance Of It is a track included in the Halo: Combat Evolved Anniversary: Original Soundtrack. It is heard several times during the Halo: Combat Evolved Anniversary campaign, including The Library. It runs for 1:21.