ΔE 16.9, loose: different enough that you should pick on purpose. Brass is noticeably darker, more muted than Old Gold.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Brass is noticeably darker, more muted than Old Gold.
The same difference applies the other way round: Old Gold is noticeably lighter, more saturated.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Old Gold on the colour wheel See Brass on the colour wheel
All matches: Old Gold equivalents · Brass equivalents