Tube screamer/Compression

[Ripper]

Are boxes like a tube screamer the same as compression?

[Mini-Strat_Maine]

deepblue said:

Are boxes like a tube screamer the same as compression?

Tube Screamer is actually an overdrive. A compressor is a whole 'nother animal. See www.harmony-central.com/Effects/Articles/Compression/ for more info.
The bottom of the page where I found the above link (www.harmony-central.com/Effects/effects-explained.html) also has links to some PDF tech notes from Alesis. Their first one makes an analogy about "an engineer with his hand on a fader and his eyes on an input level meter." I still may not understand compression, but I can grasp that much, anyway. After that, I just figure it's all done with mirrors, smoke, and fine wires.

[RandomHero]

Compression is really pretty simple.

A guitar is an instrument with a large dynamic range. That meaning it can produce sounds from the tiniest nuances to the most blaring, fret-rattling chords, and that's all good and well, because it's what enables the instrument to provide such character.

Compression is taking that dynamic range and flattening it, so let's say that by RandomHero's Imagined Sound Intensity Level System of Measurement (RHISILM for short =D ) where 0 is just brushing the string with a finger and 10 is digging it hard with your stiffest pick, a compressor pedal takes that wildly varying input signal and maintains it at a 7, if that's where you prefer.

It's good for solidifying gain sounds or just adding that extra punch to your clean.

[Mini-Strat_Maine]

admin said:

RandomHero's Imagined Sound Intensity Level System of Measurement (RHISILM for short =D )

Sounds like a good subject for my doctoral thesis. ;D

It's good for solidifying gain sounds or just adding that extra punch to your clean.

Like "wringing" those "ringing" notes out of a 12-string. (Roger McGuinn has an onboard compressor in his Rickenbacker 360/12RM.)

[UnklMickey]

RandomHero's explanation was elegantly put.


there are a few more points about this, that i'll mention.


probably a bit more clumsily.



compression can be achieved in different forms. limiting, upward compression, and downward compression.

limiting doesn't affect the signal until it reaches a certain "threshold". after that threshold is reached, the gain of the circuit is reduced so that the output never exceeds that certain level.

upward compression increases the gain of the circuit when the input signal is below a certain threshold so that output is closer to the reference level. it is often the case that the amount of compression varies with the input signal. if the input signal is for instance 30 dB below the reference level, the output might be 15 dB below. if the input increases to 10 dB below the reference level, the output might be 5 dB below. at the reference level and above, the output is at the same level as the input.

downward compression decreases the gain of the circuit, so that when input signals are above the reference level the output is above the reference level, but not by as much. it's exactly the same as limiting, only different.

in any of it's forms, we expect a good compressor to be clean. it should affect the volume of the signal, but not the waveform.



overdrive and distortion pedals are meant to change the shape of the waveform.

in the process they usually also do some limiting, or downward compression. it's not an added feature that you're paying extra for, it's inherent in the way they accomplish the distortion.


well, that's probably way more than you wanted to know.

if your head hurts from this, just go back and read what Doug and RH wrote.


unk

[Mini-Strat_Maine]

unklmickey said:

well, that's probably way more than you wanted to know.

if your head hurts from this, just go back and read what Doug and RH wrote.

I like the way you and RH explained it. Made me appreciate my DynaComp and (Analog Man) Dyna/Ross that much more.

[jester700]

unklmickey said:

limiting doesn't affect the signal until it reaches a certain "threshold". after that threshold is reached, the gain of the circuit is reduced so that the output never exceeds that certain level.

downward compression decreases the gain of the circuit, so that when input signals are above the reference level the output is above the reference level, but not by as much. it's exactly the same as limiting, only different.

in any of it's forms, we expect a good compressor to be clean. it should affect the volume of the signal, but not the waveform.
unk

Good info here and by RandomHero. Just a couple more notes:
1) Most (all?) compressors you'll hear are downward compressors - they're the standard fare. Most have a gain stage to boost output after compression, but though this makes the comp louder (and seem like an upward comp), it's not
2) The difference between a limiter and a compressor that unk referred to is simply the ratio used. Unk mentioned the threshold. Once the signal reaches that level, the ratio stting tells it HOW MUCH to allow the signal to change. A 2:1 ratio means "allow 1dB of change for every 2dB the signal goes over the threshold" that is, if the input signal goes 10dB over the threshold, you'll only get 5dB more at the output.

As a practical matter, once you get to a ratio of over 10:1, it's usually considered limiting.

Note too that compressors and limiters DO change the waveform, but they do it in a gentle way that doesn't change the harmonic structure (I think this is what unk meant) - mostly because they're slow devices. But take a brick wall limiter, set it to its fastest attack & release times, and put it on a bass - you'll hear the clipping. It's lopping off the tops of the waveforms like a "square wave" type fuzzbox would.

Note that most of these settings aren't on guitar boxes - most of those are preset in all but threshold & output gain - because there's only one thing likely to be plugged into them - an electric guitar.