Amplifier compression

2 posts in this topic

So I've noticed this, and can't precisely explain whats happening, so I'm open to viewpoints.


if you take any electric or pickup-ed guitar and run it through a line-in, direct input, etc.


Taking a send from that same guitar through an amplifier, even a 10 watt practice amp or anything,

You'll find some really smooth, lower-ratio compression (and some equalizing that will make the general tone better and could prove tricky in listening for compression) coming from the amplifier.

I could bullshit you about how tube saturation contains a natural soft-knee compression, and solid state amps emulate this, but I haven't found any solid explanations of this, and would be interested in any further information.

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You using active or passive DI's?

Basically, guitar amps are low end amplifiers. There's a reason the manufacturers haven't broken into the front of house gear where the 'big boys' play.

I'd have to see some schematics of the amp to tell you exactly what's going on - but your observation is about right. Even with solid state, there's a limit to the voltage rails supplying the FET's that amplify. These are supplied from a power supply that has a limit on current and voltage. With most decent guitar amps, even lower wattage, they have pretty beefy power supplies - all be it on the simple side. This is what typically adds weight. Now, the power supply size means that it'll produce a good whack of current but the voltage will be limited... and what does a compressor do? It limits amplitude, which is equivalent to limiting voltage. This means that you'll get compression without harsh distortion.

Distortion is generally an effect of the amp running out of 'drive' or current. Don't get me wrong - part of the inherent design of guitar amps is distortion though it was originally a deficiency of design rather than a feature. This is what gives a 'rounded' and 'smooth' sound to different amps. But they're not reaching a limit because of current which means the driver/speaker keeps moving smoothly.

You might also find it has to do with impedance matching difference between a DI and an amplifier. DI's are typically designed to be clean and noise free. Guitar amp inputs and amps in general are not - they're designed to colour the sound and create a pleasing noise to listen too. That's relative - different people find different noises pleasing so there's variation in input/pre-amp and amp stages.

You're DI then goes to a mixer - which again adds minimal colour depending on the mixer... and then into an Amp which again is designed to add minimum colour to the sound. You can add compression and distortion and all the other things via the mixer to 'make' an a guitar amp sound.

Guitar amps also don't go much into harmonic distortion and other fidelity limits. Again, adding colour to the sound and part of harmonic effects will be some compression.


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