Your brain is lying to you. It’s an incredibly powerful organ that is constantly using stimuli in your environment to construct a mental picture of the world around you. Sometimes, the techniques it uses to achieve this may not be an entirely accurate representation of your surroundings. In the context of sound engineering and production we can harness this cerebral trickery to create audio illusions that instantly make our music magical.
The Haas effect or Precedence effect was outlined by Helmut Haas as the mechanism by which our brain localises sounds within our environment. In basic terms we establish the direction of a sound by determining which ear is the first to perceive it along with its reflections off of the surfaces around us. The delay between our ears can be anything from 1-30ms. You can use this to add a more realistic stereo width to a sound in your DAW.
When you’re forced to deal with a sound that is particularly loud, as a response, the muscles in your inner ear are forced to contract. This limits the amount of vibrational energy that can be transmitted to your cochlea (The bit where the vibrations are translated into messages to your brain) and protects you from going deaf. Even though this reflex leads to a reduction of the noise’s volume, your brain still interprets this as a loud, sustained noise and works to fill in the gaps. This means that the sound can sometimes appear louder than it actually is. When you’re at a fireworks display, you’re almost imagining the roaring bangs as they explode.
This illusion can be harnessed in music production. If you have an impact sound that you’re using to introduce a breakdown, as an example, you can trick the brain into believing that it’s more ferocious than it already is. Artificially reducing the volume of the sound immediately after its initial transient will, strangely, add more weight to the sound. This technique is used all the time in sound design for films.
Thinking logically, it’d make sense that two sounds played at exactly the same volume would be perceived as equally powerful. The strange, illogical thing is, this isn’t entirely true. If you were to listen to a short, punchy kick sample and a sustained synth stab at the same level, the synth stab would appear louder. This is because our brains immediately determine sounds with a longer decay and sustain as more powerful, even if they aren’t playing at a louder volume.
This can be a useful trick to use with drum sounds. If you raise the decay of a drum hit, it will be perceived as louder without increasing the volume of the original sound which can lead to your mix clipping. This will also make the sample appear far more powerful as well.