March 7, 2013


What is Hi-Z vs. Lo-Z?  What do people mean when they talk about “Mic Level”, “Line Level”, and “Impedance”?


First, let’s look at Mic Level sources.  These are considered to be either at Hi-Z or Lo-Z:

Hi-Z – High Impedance, High Voltage, Low Current
Keywords: Guitars, Basses, Instruments; Short Cable Runs, Better Sustain, More Interference.

Most of us will come to associate Hi-Z impedance equipment with things like guitars, basses, and 1/4” connector plugs.  Inside of a Hi-Z cable, there are only two conductors: a “positive” and a ground.   Since there is no negative cable (such as in a Lo-Z cable) to balance the positive cable, both capacitance and reactance suffer with increasingly longer cables.  In layman’s terms, this means your sound loses quality and gets noisier once your cable exceeds roughly 15’ – 20’.  (Ever wonder why it’s hard to find guitar cables longer than 20’?  Now you know why!)

Fun Fact: Vacuum tube circuits have naturally high impedance.

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Guitars and Basses are Hi-Z

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Most Microphones are Low-Z, including this Shure SM58
Lo-Z – Low Impedance, Low Voltage, High Current
Keywords: Microphones, Pro Audio Equipment; Longer Cable Runs, Better Signal Quality; Less Interference.

Most people tend to associate Lo-Z impedance equipment with microphones, professional audio equipment, and XLR connectors.  Because Lo-Z cables contain a positive conductor, negative conductor, and a ground, it’s possible to have cables up to several hundred feet long without significant signal degradation or outside RF interference.

Fun Fact 2: There is a lot of discussion in regards to why guitars don’t use Lo-Z outputs.  To make a long story short, most guitarists don’t like the tone of Lo-Z pickups; most guitar amps and pedals aren’t designed for operation with low-impedance guitar outputs; and Lo-Z setups would cost much more.

Now let’s look at Line Level sources.




Common line level sources include CD players, MP3 players, mixers, and other pro audio equipment.  In the recording industry, though, there is often some finagling to be done to get our signal from Mic Level to Line Level.

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This Vintech 473 is a really kick-ass, studio-quality mic preamp
In order to bring a Lo-Z or Hi-Z source up to Line Level, we must use a Preamp.  Preamps such as my GAP Pre-73 are very good at taking a quiet source and making it louder without introducing unfavorable noise, and sometimes they’ll even add favorable noise, or “color”, if you will.  This is what people refer to when they talk about the relative “coloration” or “transparent” qualities of preamps.

If you plug a Hi-Z source into a Line Level input, such as on a Mixer, you’ll find it’s pretty faint and hard to hear.  When you start cranking the gain to get it up to an audible volume, you will also have amplified all kinds of undesirable noise.  No dice.  With Lo-Z sources, such as microphones, the input signal will be even quieter and require even more gain to get it up to snuff.  (By the way, Microphone voltage starts out around 2 millivolts and ends up as high as over 1V, so you can begin to understand the importance of solid preamp construction.)  Hence, this is why most mixers have specific inputs for Line Level sources only; the XLR inputs are there for you to put your microphone into, after which the onboard preamps will do the proper boosting.

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The picture says it all: notice the Hi-Z input and Lo-Z output
What about guitars, then?  You can’t plug them directly into the Line Level input or the XLR Mic Input.  Instead, you will need to use a DI Box to transform the unbalanced Hi-Z signal to a balanced Lo-Z signal, after which your guitar signal can be safely connected to the XLR input on the mixer.  Now that the impedances are matched, you won’t have all kinds of gnarly noise when you crank the gain knob.  Instead, it’ll sound pretty good for a change, and you can pat yourself on the back for getting it right!  Of course, you can always avoid the DI box by mic’ing your instrument or your amplifier, but this isn’t always doable.

Finally, another important feature of line level equipment is to figure out whether or not it’s considered +4 or -10.  Most equipment that functions at line level will have a switch, allowing you to adjust one way or the other.  Either way, you just want to make sure you’re keeping all elements in your circuit/system matched so you don’t have unnecessary signal loss or degradation.

Please let me know if you have any questions.  I'll leave you with a helpful video I found on YouTube explaining DI boxes in more detail.  Cheers!

8 comments:

  1. Setting aside the sound quality...
    If I connect a HI-Z INST in a Mic input, can it damage my equipment?
    In other words...
    Hi-Z instrument signals have more power(I think) than mics, so can it hurt my preamps?
    I know, would be better to use a direct-box, but without it its sounding good enough to me.
    Thanks!

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    Replies
    1. Renato, what type of preamp are you using, and how exactly are you connecting your instrument to it? Some mic preamps have dedicated inputs for instruments, in which case that's what they're designed for -- to accept unbalanced TS cable inputs. If this is what's going on, then you are hooking everything up as the manufacturer expects.

      Depending on the pres you're using, there are other scenarios, for example you may be connecting your guitar via the unbalanced TS cable to a line level TRS input, or to a mic level TRS preamp input.

      In the case of connecting your guitar directly to a line level TRS input, the TRS input is expecting a much stronger signal, and you will end up needing to boost the signal quite a bit to bring your guitar up to volume. There is also an impedance mismatch, since the average guitar signal is 20k-40k ohms or more whereas line level inputs hover around 10k. This will lead to an inferior SNR (signal to noise) ratio, and the required boosting will amplify noise, hum, RF interference, etc. coming from the unbalanced signal.

      In the case of connecting your guitar to a mic level TRS input, the use of the TS cable in the TRS input jack will unbalance the signal and you will again have an impedance mismatch, leading to potential hum/noise and signal degradation. Specifically you will find loss of high end in this type of scenario, too. This will be exacerbated further by longer cable lengths. Technically, I most equipment should survive such a connection, but it is not a recommended configuration. As a disclaimer, it could lead to damage depending on how the manufacturer of a particular piece of equipment has it wired up.

      Generally speaking you want the impedance of your input to be 7-10 times higher than the source output for ideal sound quality. This is why we use DI boxes. This minimizes voltage drop and current draw, minimizes distortion, and allows max transfer of voltage. In layman's terms, the DI box maximizes signal fidelity and eliminates noise issues and impedance mismatches.

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  2. I want to connect a shure beta58a to a boss gt10b processor. Can i plug it directly or do i need a lowZ to highZ DIBox/cable in order to work propertly? Will i lose audio quality ifi connectidirecly and is that even a option? What are the pros and cons? Thx

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  3. Low and high impedance is totally separate from unbalanced and balanced. You say "since lo-z cables have a positive conductor..." While it's typical for unbalanced cables to carry hi and balanced to carry low, it's two separate things going on. You can have a balanced or unbalanced signal of any impedance. For instance, some keyboards have a low-z output. They're still a quarter inch, unbalanced output, however.

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  4. I've been playing - and recording - music for years, mostly simply acoustic stuff, couple of guitars & 2 or 3 vocal tracks. I've always worked around hi and lo impedance devices, locking settings where the recording interface manufacturer suggested, without ever actually knowing what the heck the difference between Hi-Z and Lo-Z actually was. I did a google search to get the answer, and out of all of the convoluted techie-jargon crap that I came across, your article and explanation are by far the clearest and simplest, and actually make sense...thanks for this!!!

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  5. This article equates Hi-Z with 2 conductor unbalanced circuits and Lo-Z with 3 conductor balanced circuits. Unbalanced circuits can be either Lo-Z or Hi-Z. Doing some google searches suggests that most unbalanced circuits are Lo-Z these days. Historically this was apparently not the case.

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  6. Hi Steven, your article is very clear. I've been combing the Internet for hours to try and understand the best way to run my saxophone through guitar and synth FX pedals, and reduce impedance issues. One basic question would be is it useful to run the mic through an Audiobuddy preamp (which I have) first? Or should I buy an impedance matching adaptor instead? Also fearful/curious about other unwanted noise issues that could crop up from so much 1/4" cabling etc. . . . Any light on the subject would much appreciated!!

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