ABLM is a gain control which enables level matched and sample accurate AB comparison of FX chains.
Most DAWs can easily enable/disable (AB) single plug-in or even whole FX chains, but in most case there is an audible loudness difference between both cases. In order to compare the impact of a plugin chain objectively the loudness of the incoming signal should match with the loudness of outgoing signal.
Comparing the plugin effect at equal loudness levels avoids the “louder is better” – pitfa
