Do some overdrives act like compressors?

Discussion in 'Effects, Pedals, Strings & Things' started by LBXPDX, Sep 11, 2019 at 7:09 PM.

  1. LBXPDX

    LBXPDX Member

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    I have a Klone built from using 2014 Aion Refractor board and I noticed the bass gets tighter and less boomy when it’s on. It is very noticeable on one guitar that is boomy in the neck. I claim ignorance to the world of pedals, so if this is a foolish question, my apologies.
     
  2. Humble Texan Fan

    Humble Texan Fan Member

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    Well, some ODs do compress a bit and add sustain. They can have a natural EQ that is middy or rolls off lowend as well.
     
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  3. fiveightandten

    fiveightandten Member

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    The Klon circuit rolls off low end, which is why it sounds tighter and less boomy to you. That has nothing to do with compression. A lot of drive pedals roll off low end because applying gain to low frequencies can muddy up the sound. The low end is the first thing to cave in.

    But yes, overdrive pedals compress the signal by a huge degree. In fact, you can use compression in place of overdrive...you get the sustain and dynamic response, without the break up.
     
  4. Dr. Tinnitus

    Dr. Tinnitus Member

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    Yes they can. But you need to think about the effect of the compressor. Lots of "colored" compressors can roll off the high end and add a spongy feel to the tone. Many ODs do the same. There are strong similarities with how a compressor and an OD can effect the overall tone.
     
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  5. MogwaiBoy

    MogwaiBoy Member

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    Technically all of them do, since you are reducing dynamic range essentially like a compressor. And the higher the gain the more compressed (full distortion/saturation).
     
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  6. Glitch Magnet

    Glitch Magnet Supporting Member

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    Well, they don't compress in the conventional sense. A compressor limits overall signal level, while an OD clips the waveform. A compressor generally keeps the waveform intact and just reduces it's amplitude. An OD actually chops off the waveform peaks, which attenuates and distorts the signal.

    Both result in a reduction of dynamic range, smoothing signal peaks and increasing sustain. The obvious difference is that clipping produces distortion.
     
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  7. Bluesful

    Bluesful Supporting Member

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  8. Vaibhav Joshi

    Vaibhav Joshi Member

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    Yea, same experience here.
    I play through an SS amp, clean. So there is no compression at moderate volumes.
    But most ODs, even at minimal settings/gain add some compression which makes the sound richer.
    What I've found with my compressor at 18V is that it's too 'trebly'. Like too much!!!
     
  9. s3gle

    s3gle Member

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    I'd say no, if you're talking about your standard diode type distortion among the circuit variants that mimic or actually are tube breakup

    Technically that may be wrong, but obsessing over details as to what determines the difference, like say the op amp, tends to lead objectively nowhere. If I could get compression by increasing the clipping somehow from drive with volume at unity from a Tubescreamer, I would. Instead it sounds like duh, so no, it's different. :rolleyes:
     
  10. bean

    bean Supporting Member

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    They are similar in that both utilize a dynamic input to produce a proportional output. But, a good OD adds pleasant distortion with added harmonics and a good compressor adds sustain and reduced dynamics without adding distortion.
     
  11. MikeMcK

    MikeMcK Supporting Member

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    A compressor generally doesn't keep a waveform intact unless the entire waveform is below the "kick-in" point for compression... it will squash peaks, but not do the same thing as an automatic gain control... if it did, we wouldn't hear compression, we'd hear reduced volume.

    In many cases (especially in audio stuff like this) clipping and compression can have a very similar effect. If you take a hard-clipped signal and round the sharp "corners" (using a low-pass filter) you get pretty much the same thing as compression.
     
  12. sanfi4u

    sanfi4u Silver Supporting Member

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    Sorry, I'm in a @Glitch Magnet camp. Here's some reading that you may find helpful.
    Ovnilab Compression F.A.Q.
    Jim Carr - Bass Compression
    Soundfly - the Basics of Compression
     
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  13. amz-fx

    amz-fx Supporting Member

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    Overdrives add limiting and compression.

    There is a difference in how much distortion (and harmonics) are added to the signal, but interestingly, a classic rack compressor became the sought-after box when it was found that the distortion that it added to the signal was very pleasing and enhanced the sound. You have heard it on hundreds of records, and an updated version of the circuit is sold by a modern marketer as a harmonic enhancer. It is more compressor than overdrive but has features of each.

    There was a type of big box compressor that used diodes as the voltage-controlled elements to generate the compression. The main difference between this and an overdrive is that the clipping was softened and modified by a control voltage derived from the audio signal. This is a technique that has not been explored in much depth for overdrives.

    A Ross-type compressor uses the 3080 OTA chip that is well-known to produce distortion if driven above a certain low signal level. Many people find this pleasing and Ross/MXR compressors are very popular. It is more compressor than overdrive but has features of each. If you drive it very hard, or mod the circuit by changing a couple of resistors, it can take on more of a soft overdrive character.

    The difference in overdrives and 3080-type compressors is a matter of degree. The percentage of distortion in an overdrive pedal will be a much larger portion of the output signal than that found in the compressor.

    There is limiting and compression in overdrive pedals (but usually more distortion than in compressors).

    regards, Jack
     
  14. spentron

    spentron Member

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    The semantics is that "compressors" compress with a minimum of other effects. An OD compresses, but a compressor is not an OD, otherwise it would be called distortion or overdrive. They vary gain, like an automatic level control, but typically not as heavy-handed as most ALCs, more controllable.

    The difference is that distortion is instantaneous, or at least down to the waveform level. Hard clipping cuts off or compresses the very waveforms and can recover instantly, with the lower level part of the waveform not touched. To keep distortion low, a compressor cannot respond immediately to a change in signal level and can take several cycles of the waveform to respond significantly. To get a fast attack response, recovery must be even slower. A control signal must be derived in order to control all this. When the compressor does respond, since the gain is varied, it affects the entire waveform equally, right down to the zero crossings.
     
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  15. MikeMcK

    MikeMcK Supporting Member

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    Well, it's not something we can vote on. Those simplified explanations of compression say what I said, but may not have been very thorough or clear. Having spent years as an engineer (in aerospace and telecommunications), compression is inherent in every amplifying component. In most generic circuits it's something to avoid, but in audio we do it on purpose. A compressor only affects peaks with magnitudes beyond threshold levels. If compression worked like @Glitch Magnet described, compression curves wouldn't have "knees"... they'd be lines that were less steep than the originals.

    If you read through @amz-fx's post above, note what he said about harmonics. If a compressor simply reduced volume without changing the signal shape, there'd be no added harmonic content.
     
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  16. Glitch Magnet

    Glitch Magnet Supporting Member

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    Of course, my explanation was extremely basic and purely conceptual. I'm well aware that most compressors and limiters exhibit distortion characteristics of some kind. Virtually all audio equipment does. I also know that the effect of overdriving an audio circuit effectively compresses the signal in that it reduces its dynamic range. My point was that the intent and method of a compressor differs fundamentally from an OD pedal, though certain traits of each cross over. You won't get "clean" compression from an OD, and you won't get much clipping distortion from a typical compressor without abusing it.
     
    Last edited: Sep 13, 2019 at 8:45 PM
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  17. drbob1

    drbob1 Silver Supporting Member

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    There are 3 kinds of distortion in audio signals: dynamic distortion, changes in EQ, and introduction of harmonics (you could argue phase as a 4th, but some people have told me that EQ and phase are two sides of the same coin). So, in the OPs Klon the following things are happening:
    1. There's a high pass filter on the input that, below a certain frequency cuts the signal to reduce bass. The Klon does this less when it's fairly clean (because of the clean blend feature) and more as it gets more distorted. Some pedals, like the Timmy, allow you to set the amount of bass cut before distortion.
    2. The soft clipping stage adds harmonics-you can describe any shape of wave by breaking it down into the harmonics it adds to the base tone.
    3. The dynamic range is reduced-the compression that others are talking about. While a studio compressor reduces gain with minimal addition of harmonic distortion, the effect of limiting gain by adding harmonics to more closely resemble a square wave and limiting gain by reducing the overall level and adding harmonics is pretty much the same...
     
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  18. sanfi4u

    sanfi4u Silver Supporting Member

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    I guess we all understand what we are talking about. Any gain stage has THD above zero by nature. But properly designed and used Class A circuit doesn't affect the dynamic range. Sure if you have any sort of clipping in the circuit (intentionally introduced or occasionally happened) it will add harmonics AND limit the dynamic range of the signal.
    So my answer to the OP question is yes, overdrives can compress the dynamic range if the input signal is high enough, but they are still very different from compressors which purpose is to change the dynamic range without adding non-linear distortion. But as there's nothing perfect under the sun compressors also add some minor non-linear distortion.
     
    Last edited: Sep 14, 2019 at 3:46 PM
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  19. sanfi4u

    sanfi4u Silver Supporting Member

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    Do not believe them. Although EQ and phase are interrelated in some circuits phase is still an important and often underestimated part of signal representation in a frequency domain.
     

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