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How do compressors change TONE ? Effects Pedals, Units & Accessories
Old 15th September 2011
  #1
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How do compressors change TONE ?

Hi all,

I've never really used compressors for much more than level control .. and almost never during tracking.

So I am curious about how compressors change TONE ?
For example, a model like the PBC-6A ... i.e specifically compressors that are NOT tube based.

i.e. How they technically achieve tonal changes, and what those tone changes normally would be (i.e. warming, thickening ect ect ect).

Thanks all.
Old 15th September 2011
  #2
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carlheinz's Avatar
 

I'm no expert here...but

Not all comps will change tone.
Some will in a subtle way
other/s like certain old tube ones are not subtle

It's the components in the audio path and how they deal with voltage that change the tone...not so much the compression itself unless the voltage swings affect the responce of other componets that are in a critiacal part of the audio path.Then there are transformers which can also change the sound depending on the make.

Every and any electronic component in an audio path will change tone by slowing down and creating a loss in voltage and then even more change in the tone through make up and recovery of that voltage down the line.Certain critical pieces in the audio path like a tube and the type of tube will react to voltage in certain way verses a solid state device.
Old 15th September 2011
  #3
Read this, audio compressor tips. its something i put together that is very straightforward and easy to understand. It has everything you need to know about compressors.
Old 15th September 2011
  #4
Gear Head
 

Compression itself is a form of distortion, an intentional one. Although amplitude and frequency are different dimentions of audio signals, they are actually different ways of looking at the same thing. So although you're working on the amplitude of a signal - which at first looks like a separate phenomenon to frequency - you are automatically affecting the frequency content. The two are inextricably linked. The way in which different compressors handle the audio will determine how audible the tonal effects are, and what their character will be. For instance, two different compressors may have very different attack and release curves regardless of their settings. These will markedly affect how the compressor follows the envelope of a signal, and thus how it distorts it.
Old 15th September 2011
  #5
Registered User
Quote:
Originally Posted by jlsgear View Post
i.e. How they technically achieve tonal changes, and what those tone changes normally would be (i.e. warming, thickening ect ect ect).
Low frequencies often have more energy than highs, so (depending totally on the source material) it's not uncommon to find that low frequency transients force the compressor into stronger compression, which effectively removes bass content from the signal.

Some compressors have filters in the sidechain, to prevent this loss of bass. So this is basically EQ - just on the sidechain - but it affects the result for the output, allowing more bass through.

Compressors are also famous for dulling the highs. To a certain extent, this is similar to de-essing. A de-esser normally has a side chain that is filtered to just respond to the "essy" frequencies (around 5k-ish). But even a basic compressor with unfiltered sidechain will appear to knock down any high frequencies that are prominent.

This sort of sounds contradictory - but the thing is, it totally depends on the source material.

Basically - whatever frequency is prominent, that's going to get knocked down. That has a similar effect to lowering that frequency with an EQ.

Depending on what you are trying to achieve, there are times it makes sense to EQ before compression, and there are times when it makes sense to EQ after compression.

Compressors can also add harmonic content - aka distortion. It's not just tubes that add harmonics. Transformers do it. But even a transformerless solid state compressor can add harmonics. FET transistors can sound very tubelike ... check out the Tech21 Sansamp range of guitar boxes to see that FETs are VERY effective at emulating tubes. Some of the popular compressors uses both FETs and transformers - gobs of color.

Whether using tubes, transformers or transistors - these components can be very clean, if used in their linear range. It's when they get pushed into the non-linear range that they change the waveform.

Think of a sine wave (pure single frequency with no harmonics). If you push this through a circuit that can't recreate the voltage accurately - you change the shape of the sine wave. If the sine wave clips, you get very close to a square wave (approaching infinite harmonics). Or anything in between.

If your compressor is VERY fast, it can change the shape of a waveform simply by "biting" into the waveform (especially the slower bass frequencies). An 1176 on fast is famous for this.
Old 15th September 2011
  #6
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audiogeek's Avatar
 

Answering this question is like just begging to be flamed... but I'll give it a shot.

Forgetting the impact of electrical component distortion in hardware compressors for a moment...

...and assuming the entirely subjective adjectives of "tone" are mutually understood and agreed upon by the general public...

The "tone" of a sound source is a function of the relative amplitude of the complex wave's various harmonics. Less higher-order harmonics = a "warmer" or "darker" tone; more higher-order harmonics = a "harsh" or "brighter" tone.

When you pass that delicate balance of relative amplitudes through a device that uniformly limits the dynamic response of the whole wave, particularly if you are doing so very aggressively, you're basically changing that balance. Whichever harmonic frequencies were "louder" than the others in the complex wave are now pushed back to an amplitude that is closer to the other, previously quieter, dynamics.

Now start playing with the various parameters at your disposal (attack, release, ratio, etc) and you can further fine-tune your tone-sculpting compressor.

It's not unlike changing the "depth of field" setting on a camera (I mean a real camera, not one of those automatic point-and-click things that are so ubiquitous these days). Sure, the person in the foreground is still there, the pastoral scene behind them, but the picture can somehow be made to feel "flatter".
Old 15th September 2011
  #7
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Unclenny's Avatar
I love compression threads.

Three excellent answers already.
Old 15th September 2011
  #8
Maybe someone said this indirectly already, but one very obvious answer is that for most types of sounds you'd use a compressor on, i.e. those with some sort of transient attack, there's more high frequency usually in that transient attack than at any other point in the sound in most cases. The compressor usually, though not always, lowers the transient attack, though sometimes it can emphasize it depending on the attack time and the nature of the transient.

So the compressor can make it duller or brighter, in an apparent way. Consider an acoustic guitar or snare drum. That initial hit is going to be brighter than the trailing sustain or room ambience. If you use a fast attack, you'll lower the initial attack and probably you'll raise the makeup gain, so you are reducing the brightest portion relative to the less bright portion. If the attack lets the attack through, then pulls down on the trailing tone, it makes the attack stand out even more sharply and it might sound even brighter since it's now closer to being all attack.

You can easily test this with drums by just pulling down the attack knob, assuming it can get down under a couple ms attack time, fast enough to kill that transient pretty heavily. And if you emphasize the attack and suppress the after-ring/ambience a lot, it can become seemingly dryer, brighter, and more up front.

It all depends on the sound obviously, but this is one way, or two ways, that it *can* affect tone, and the ways that I most often experience it happening, leaving aside obviously any purposeful imposition of tone alteration that the design of the compressor might impart in and of itself.
Old 16th September 2011
  #9
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popmann's Avatar
There are two methods is changes tone. The singal path itself--input/output amps/tubes/transformers...and the compression itself, in altering the dynamics is actually altering the frequency relationships--which ultimately are what make up the "tone" of an instrument. Say you have a bass heavy "tone"...you compress it, and to oversimplify, it will reduce the ratio of bass to treble by bringing the signal down when the bass peaks, which will happen more in a bass heavy tone.

Clear as mud?
Old 16th September 2011
  #10
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audiogeek's Avatar
 

Quote:
Originally Posted by popmann View Post
There are two methods is changes tone. The singal path itself--input/output amps/tubes/transformers...and the compression itself, in altering the dynamics is actually altering the frequency relationships--which ultimately are what make up the "tone" of an instrument. Say you have a bass heavy "tone"...you compress it, and to oversimplify, it will reduce the ratio of bass to treble by bringing the signal down when the bass peaks, which will happen more in a bass heavy tone.

Clear as mud?
Wow, that is pretty much exactly what I was trying to say, in about 1/4 the word count. Bravo.
Old 16th September 2011
  #11
But that's more related to bus compression, not individual track compression where there would only be one instrument involved.
Old 16th September 2011
  #12
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popmann's Avatar
No...not really...unless you interpreted "bass heavy" to mean "bass guitar heavy". I just recorded a track with my FralinVVT (and it's 15" speaker) with the 121...it's a fairly bass heavy tone. Or was when I threw the mic down. Too much so...so, I moved the mic far enough back to avoid proximity effect, and flipped the bright switch on the amp--which changes the tonal balance between lows and highs at the source level. One instrument. One track. I could've also slammed it with the La3a, and that would've brought the bass down and pick attack and mids up in relation to the lows. But, then, I would have also altered the dynamics of the track, too....so, I did what I did...

It's an over simplification of "tone"...which is more technically frequency relationships over the range of dynamics...and you can certainly HEAR that more dramatically on a bus full of tones (thus a sort of super complex ever shifting frequency relationship)...but, it's the same principle.

To further expound on the circuit...I can run a singal though most of my outboard--be it the clean Speck ASCT or the LA610 or my vintage La3a--without doing ANY "processing" on the units, the output will change tone noticeably. This is why we collectively love big analog desks-each signal is changed and given a certain tonal color by passing through the input amps...the EQ circuits...the summing busses...but, I digress into wi****l memories.
Old 21st December 2011
  #13
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Swurveman's Avatar
This is an old thread, but what the heck:

This Michael Brauer quote fascinated me: "A lot of what I was doing was about feel. I fell in love with the sound of compressors. They weren't necessarily compressing, it was just the sound of them. Very often I would use compressors as an equaliser. Eighty percent of my compressors are used strictly for tone.

There may be technical reasons for how compressors effect tone, but I'm going to send sounds through my compressors and just listen to the result.
Old 21st December 2011
  #14
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nosebleedaudio's Avatar
 

Depends on the compressor and HOW much compression, as far as "Tone" change goes.
Old 21st December 2011
  #15
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Quote:
Originally Posted by jlsgear View Post
Hi all,

I've never really used compressors for much more than level control .. and almost never during tracking.

So I am curious about how compressors change TONE ?
For example, a model like the PBC-6A ... i.e specifically compressors that are NOT tube based.

i.e. How they technically achieve tonal changes, and what those tone changes normally would be (i.e. warming, thickening ect ect ect).

Thanks all.
any nonlinear fx like compression will create harmonics
that would change timbre

not sure about tone unless that is the same as timbre to you
dont know any compressors that change tone in any way that you can control
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