Perceived loudness vs db count

[Monowan]

Why does a sound sometimes appear much quieter than another sound peaking at the same db or even lower? Best example is, when setting up drum bus compression (something I still struggle with, but I'm so fed up with it I won't bother to start yet another thread), why does a heavily squashed signal still sound quieter than the uncompressed version even when I use make up gain to bring it at the same "mathematical" level ?

[Parnassa]

It has to do with how our ears work. Compressors minimize the dynamic range of a signal. Sounds with less dynamic range can seem quieter even at higher levels because it's the contrast between the highest and lowest parts of a waveform that help give us our impression of loudness.

My terminology probably isn't the most precise, but I hope that idea makes sense. Use your ears when it comes to compression and mixing in general, the meters can be misleading sometimes.

[hasezwei]

you see the trick with compressing drums is to NOT squash the signal
if you reduce a drum hit's amplitude after the initial transient you will still percieve the drum as being loud, even when the tail's volume is reduced.
that will give your drums a sharp, defined sound as opposed to the heavy/punchy sound you get from compressing with no attack (which is basically raising the tails volume)

also not all frequencies are percieved equally loud at the same db levels. you can google 'fletcher munson curve' for further reference.
for example sub bass needs to be a lot louder (even with a subwoofer) compared to lets say a hat peaking at 10khz to seem equally loud to the human ear.

[Monowan]

Makes sense, thank you

[Artie_Fufkin]

RMS, not peak levels

[NinjaEdit]

Also see the Fletcher-Munson curve.

[didi]

RMS, not peak levels

Reason #1

Also see the Fletcher-Munson curve.

Reason #2