Compression and sag - obviously a key aspect of any rig but I, probably like many, have not given it much thought and have only really engaged it by experimentation, feel and knob-tweaking. So whilst both reduce dynamic range aside (one from a stomp box and via a power amp characteristic) would anyone care to explain the difference between the two things?
Whilst we're at it I would also be interested to hear arguments for and against compression/sag in certain music contexts and how individuals utilise and employed it within a rig.
Comments
It's just that sag is a byproduct of having a limited amount of available power for each amplifier stage as all the stages try to pull juice from the same source, and unless you're designing the amp yourself is uncontrollable - it just is part of what the amp does. And it can have side effects such as inter-modulation between gain stages, and with the wall voltage, that introduce different harmonics
Compression is designed to give a controllable reduction in dynamic range, there are different kinds of circuits that do the job in different ways and with different effects on the audio, but you get various controls to influence how it does it.
Bandcamp
Spotify, Apple et al
"Sag
Controls power amp sag or compression 0% tight, 50% normal, 100% more touch for dynamic sustain.
Lower Sag values offer a "tighter" responsiveness for metal and djent playing; higher values provide more touch dynamics & sustain for blues and classic rock riffs. High Bias (closer to class A) reduces the effect of the Sag control. Sag doesn’t exist in class A amplifiers since the average plate current doesn’t change.
Sag is caused by the amplifiers power supply being unable to meet the demand when the map is pushed hard with high Master. When the power sags, the amp output drops and then recovers, creating a unique compression effect with some additional, but temporary distortion when you pick hard. Unlike compressors before the amp, sag compression occurs even when the amp is already very distorted.
Large sag gives more compression, better sustain, and can accentuate pick attack. But the amp will appear somewhat less responsive especially at the low end and can get muddy."
full thread here: https://line6.com/support/topic/19115-helix-amp-parameters/