What does "headroom" mean in reference to overdrive pedals?

Discussion in 'Effects, Pedals, Strings & Things' started by Presc, Dec 8, 2016.

  1. Presc

    Presc Member

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    I get the concept of headroom when referring to a guitar amplifier - how much output can be produced before clipping.

    I've seen a lot of pedals manuals mentioning "increased headroom" when run over 9V. A pedal is a preamp clipping device by design, so what does this exactly mean? I have a PP2+ which allows me to toggle to 12V and have never noticed a difference between 9V and 12V, but perhaps it's more audible at 18V?
     
  2. Killshakes

    Killshakes Member

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    I have to admit: I've never really been sure what people are talking about when they say that.
     
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  3. guitar007

    guitar007 Member

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    I'm guesssing here...maybe the pedal is high-output-pickup friendly??
     
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  4. Jeremie Legault

    Jeremie Legault Member

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    Well I can answer what I perceived when I went from using a 9v adapter to an 18v with my EP booster. What happened is that the sound was just less compressed, and there was better note separation and a more dynamic cleaner sound.
    So I think that headroom in pedals is a similar concept to headroom in amps. The same pedal at two voltages (ALWAYS check your manual or manufacturer website before testing!!!) will be more dynamic at the higher voltage, and will clip or compress earlier in the lower voltage.
     
  5. dickjonesify

    dickjonesify Member

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    ^That

    Higher output volume before clipping and less compression.

    It means the same thing but it's referring to clipping in the pedal as opposed to an amp.
     
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  6. MoonshineMan

    MoonshineMan Member

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    I have a feeling that it's closer to how much INPUT before clipping. OD pedals with low headroom can sound cool, but the dynamics will work differently. Think of it like plugging into a tweed Champ and a Deluxe Reverb, but don't consider the volume differences. Almost anything will override the champ, so it doesn't spend a lot of time clean (even though it really sounds good clean!!), and the OD is fat and splat and constant. The Deluxe eases into clipping more gradually because of more headroom, making it easier to access all the little nuanced stuff between crystal clean and full-blown dirt.
    It may also help to think of a fuzz pedal cranked up with your guitar rolled all the way up as well. You might be able to get something non-fuzzy by barely touching the strings, but it runs out quick, right? Roll your volume back and you can still pick hard and reach Fuzz but you can also pick light and clean up a little or a lot.
    I think a lot of it has to do with voltages. On the old tube charts, higher voltages showed more headroom before the clipping started, allowing a wider voltage swing (aka "input signal") on the grid before distortion occurs.
    Well, here comes my bus.
    Hopefully I've confused you more.
    ;)
     
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  7. theroan

    theroan Member

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    How loud it can be without breaking up.
     
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  8. Presc

    Presc Member

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    I think that makes sense - so essentially, at a given point on the gain knob, higher voltage will equal lower clipping, which also produces greater dynamics since the signal isn't getting "squashed" as much by the clip. Thanks for the replies so far.

    If I may probe further, how is that different than turning the gain knob down? With the Deluxe Reverb versus Champ analogy, we're talking about the output section. The clipping is innately tied to volume. With a pedal, you set your gain, and then set your level. I've never noticed the level setting on the pedal impact the amount of gain/compression, or felt like I've had a shortage of output volume from any modern overdrive I've owned.
     
  9. dickjonesify

    dickjonesify Member

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    Agreed there but modern is the key. They get much louder than they used to, in general. Even the output stage is an amplifier, capable of clipping (as I understand it) so the tube amp analogy still holds true.
     
  10. DaveKS

    DaveKS Member

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    With every audio design it's a cascading series of circuits, you may increase voltage to say even a clean boost pedal like a eqd tone job at 18v, at 18v you really can't induce clipping on any of its knobs very easily, only by cranking all the eq knobs way, way up can you hear any clipping in its output stage. But that doesn't mean you can't get clipping on its input stage if you hit it with a hot enough signal.

    Where any stage of a device, be it pedal or amp, runs out of headroom is dependent on its circuit design. You can't just say here's where this pedal runs out of headroom. Is it the pedal itself that's running out of headroom or is it the input stage on the next pedal in chain that's running out of headroom?

    Most of us schlubs have no idea where the clipping is actually occurring in our chain, but then someone like Skreddy can probably tell you just exactly where any stage of his circuits at a certain voltage runs out of headroom at any given freq using scopes and signal generators. All we as guitarists can do is listen to that cascading series of events that we call our signal chain and throw our best guess at it.
     
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  11. MoonshineMan

    MoonshineMan Member

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    Hopefully someone else can cover it, as I'm on my phone and a full explanation would be a real pita. :)
    Turning down your volume reduces the voltage swing to something the first input stage can handle. In an amp, the preamp feeds the output and both sections can clip. In a pedal (if I have this right), the "preamp" or gain stages feed a volume control, which just passes signal or bleeds it to ground. So in an amp, you can keep the preamp clean and pump the output section and the power tubes will break up. Or you can dime the preamp, cut the MV and the power tubes will stay clean (reproducing the preamp dirt). Or you can dime both and get dirt from both. In a pedal, you can keep the gain down and the volume up and just get a boost (into the amp's input, possibly driving it to clip), or mix the two and blend the outputs a little (pedal dirt and amp dirt).
    Gain is simply voltage multiplication; the lower the input voltage, the lower the resulting output voltage. Remember that your guitar signal is nothing but a voltage, with amplitude being volume* and frequency being pitch. Gain simply increases the amplitude.
    So rolling back your guitar volume just provides a smaller input signal that perhaps the input and following stages can handle it. It kinda works like "Rather than increase headroom, decrease input".

    *volume, IF the amp can cleanly reproduce it. If it's clipping, it just gets more distorted.

    I trust this confuses people even more. :)
     
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  12. tinkercity

    tinkercity Supporting Member

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    Deals with compression typically. Usually an OD or Boost with high headroom will sound richer, fuller and ultimately bigger (more 3D) than one that is less headroom. For instance the Vemuram Shanks 3K is a treble boost meets full range boost and with the high headroom it has it's bigger sounding than other treble boosts that I've tried or boosts in general.

    All that said -- in most cases will you notice the difference? Maybe not... I notice that when rolling the volume knob back on the guitar and using a pedal having higher headroom helps to keep the signal bigger rather than sounding smaller.
     
  13. Fulldrive-1

    Fulldrive-1 Member

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    This. A OD pedal with "headroom" will distort and compress, but won't be completely saturated, even with humbuckers. Try a TS variant at max gain, and then do that with a Rat. The Rat is totally saturated but the TS still lets some picking dynamics show through.
     
  14. rumbletone

    rumbletone Silver Supporting Member

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    But for OD pedals that utilize diode clipping - which is most, but not all, of them - wouldn't the headroom be capped by the forward voltage of the diodes? The op amp (or other amplification device) itself would have higher headroom before clipping, but can anyone explain how you can have higher headroom in the circuit overall when diodes are clipping the signal? Is the analysis different for soft clipping vs. hard clipping diodes?
     
  15. OverDrivenGtr

    OverDrivenGtr Member

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    I find the level control on most modern overdrive pedals can most definitely have an impact on the amount of gain/compression, especially when said pedal has a ton of output available and I run the level way past unity volume of the amp. However, I believe you can't just look at the pedal in question, you have to look at your rig as a whole. I think it depends so much on the amp that the pedal is pushing. Take a Fender Twin Reverb for example, tons of clean headroom all the way to ear splitting levels. If you put an overdrive pedal in front of the Twin and set the level control to unity volume, you now have a dirty sound at the same dB as your cleans. Now if you start to boost the level control above unity, you are most likely going to hear the same basic clipped signal, just louder. The Twin has massive headroom so pushing the level on the pedal isn't going to add a ton more gain or compression, it will have a similar effect as raising the volume on the amp itself, although possibly with a bit more color depending on the overdrive circuit. You do have to take into consideration though that changes in volume can cause a perceived change in EQ and breakup character, although if you are already pushing a decently loud gig volume, this will be subtle at best. I notice these changes most when going from bedroom practice levels to gig levels, where there is a big change in volume.

    Now take a Fender Deluxe Reverb for the next example. It doesn't have near the headroom of the Twin once you start pushing it to gig volumes. So say I dial in a loud edge of breakup sound, not too dirty but not totally pristine clean either. Now I put that same OD in front of it as I did with the Twin, same settings at unity volume. If I start pushing the level control past unity, at first I will get a raise in volume with the overall clipped tone staying the same. But when the Deluxe runs out of headroom, the level control will start to add saturation and compression without anymore added volume. Just like the actual volume control on the amp, once you hit about 6 or 7, it is all just more grit and grease after that. It is still deafeningly loud without earplugs, but it wont stay clean all the way up there like the Twin.
     
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  16. spentron

    spentron Member

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    It's a subjective, nonscientific use of the term. The definition of headroom is the difference between the present level and distortion, if you get any distortion at all you're out of headroom. With guitar's wide dynamic range you could think of the "normal" level as a medium playing level, if distortion only occurs when digging in then the term headroom wouldn't be completely wrong, except it's headroom you're actively "using" which is still in contradiction to the original intent of the term, which is range you're NOT using. E.g. running a 30 watt amp at 10 watts has more headroom than running it at 20. Overdrives are simulating running that amp at 30 to 60W.

    As soon as distortion is occurring at normal playing levels, the meaning of the term becomes arbitrary.
     
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  17. Blues Lyne

    Blues Lyne Member

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    We usually talk about clean headroom, and that's the correct use of the term, but headroom with distortion is a similar concept. You could think of it as dynamic headroom. My understanding is that it refers to how much room you have between the signal level going into the device and the point where the signal is completely saturated and the level can not be raised any farther, even if the input signal is increased.

    If you dig in, or you turn on a boost before the pedal and there's no increase in volume, you are out of headroom. If the signal is distorted, but you can still increase the volume by increasing the signal before the distortion device, you have headroom. In practical terms, it's more about dynamic range and compression.

    You could think of it as a person standing in a room. Headroom is how high you can jump without hitting the ceiling. As it's usually used, the ceiling is clipping. As it's sometimes used with distortion devices, there ceiling is the point where you can't get any louder.

    The question about getting more headroom by increasing the voltage in a pedal with diode clipping is a good one. I don't think it would change the point where diodes are clipping, but it could give more headroom in other portions of the circuit.
     
    Last edited: Dec 9, 2016
  18. kakev

    kakev Member

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    To talk about headroom with dirt boxes is nonsense. Though if they are able also to pass the totally non-clipped signal when on then the term might have some relevance.

    Recent years it has become the norm to talk about gain stages, headroom and such. It used to be all about transparency, true bypass and haunting mids. Buzzwords and bollocks.
     
  19. Rydell

    Rydell Member

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    I think higher power supply voltages might well be a shuck with some pedals. The supply voltage is generally padded down by resistors for various jobs inside the pedal which may be running at only 4.5v. The standard 9v is kind of an arbitrary figure and pedals can certainly be designed to take a higher supply voltage but there are still limits imposed by the components. If 18v is padded down to the 4.5v required by the design, is there really going to be much of a sonic difference? With a drive pedal, more headroom can usually be attained by turning up the level and turning down the drive. While I'm sure there are some clever exceptions, the current trend reminds me a little of pedal builders stacking op-amps for more headroom a few years back. I guess I'm wondering to what extent it could be a marketing gimmick. I've got a few pedals that will run at 18v but haven't heard much I can't get by working the knobs.
     
  20. fr8_trane

    fr8_trane Supporting Member

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    Headroom with pedals refers to VOLTAGE headroom. Most pedals run at 9v. There are now a slew of pedals that run at 18v or higher. The Klon was one of the first pedals to include an internal voltage doubler so that using a standard 9v power supply still provided 18v to the pedal.

    Now what are the effects of higher voltage? Typically if you take a 9v pedal and give it 18v (assuming it can HANDLE 18v without blowing up) it'll be louder, have less gain and less compression/more dynamics.

    FWIW I find OD/dist pedals that were designed to run at 18v are just more dynamic and closer to the feel of an amp than their 9v cousins (check out any of the Maxon 18v Tube screamers versus a 9v TS9). 9v pedals seems REALLY compressed by comparison which is cool and has its own benefits but if your looking for a drive pedal that most closely approximates the feel of a tube amp I think 18v pedals DOMINATE that niche.
     
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