There are a lot of exciting things we can do with audio signals — but level matching usually isn’t on the list. Adjusting the volumes of two or more audio sources so that they have equal volume when comparing them isn’t something that usually gets people’s creative juices flowing.
Level matching usually isn’t as simple as turning up the fader volume at some point in the signal chain of the quieter signal. If two signals have differing peaks, they still won’t sound even. The best way to level match signals starts with having a good metering plug-in that offers accurate RMS metering.
Read more about this here: https://www.sweetwater.com/insync/level-matching-demystified/