The New York parallel compression drum mix technique is where you send a drum mix to a stereo bus and then apply compression to the bus and feed that signal back into the two mixes. It can be very subtle or obvious depending on the amount and character of the compression, and how the compressed signal is fed to the stereo bus.
However, at low volume, you get both preserved transients and the loudness from the compression thus, you’ll get a different result from compressing the tracks. Moreover, when the song gets louder, the effect of the compression on the bus is less prominent because the uncompressed tracks swell up and dominate the mix.
Read more about this here: https://www.prosoundweb.com/channels/recording/in_the_studio_dynamic_eq_for_vocals/