Using a Tube Screamer to Tighten a Guitar Signal

[silverwulf]

I know that a lot of guys here us a Tube Screamer or similar OD pedal in front of their amps to boost the signal and tighten up the guitar tone. Most seem to use the Gain on "0" and then adjust the others to taste.

My question is why does a an OD pedal tighten up the guitar signal?

 

[Razorjack]

The 'tightness' comes from pushing the amp harder and thus clipping the signal more. The amp doesn't care what frequency the signal is at so any frequencies pushed above the clip level are basically 'squashed together' creating a much tighter, controlled sound.