Why a slow attack gives you more attack
As well as controlling dynamic range, a compressor can be an effects unit in its own right. One of the things you can do with a compressor is to make a sound more punchy or attacking. This works particularly well on kick drum and bass guitar. But don't stop there - go where your imagination takes you...
Compressors always have a control marked 'attack', calibrated in milliseconds. So you can set a fast attack or a slow attack. Which setting gives you most attack in a sound?
Counter-intuitively, it is the slow attack that leads to a more 'attacky' sound. Strange but true - read on...
A compressor operates by sensing the level of a signal. If it is above a set threshold level, then it reduces the level of the signal. When a signal rises from below the threshold to some point above it, the compressor takes a certain time to respond. This is the attack time.
Now if the attack time is set very short, so the compressor is quick to respond, then it will clamp down on the signal right away. This dulls the sound (which often leads the engineer to boost the HF EQ to compensate subjectively).
But if you set a slower attack, not all the way down but a couple of tens of milliseconds maybe, then the compressor lets the initial transient of the sound through, then it clamps down. So the 'front end' of the sound is actually boosted in level with respect to the 'body' of the sound. Hence it is subjectively more attacking.
This is something you need to try out to understand. Get yourself a kick drum sample, something mid way between soft and attacking. Then loop it and put it through your compressor - hardware or plug-in. How experiment with the attack time to your heart's content.
You will find that the attack control of the compressor can make an amazing difference to the attacking qualities of a sound.