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.
|Guitars and Basses are Hi-Z|
|Most Microphones are Low-Z, including this Shure SM58|
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.
|This Vintech 473 is a really kick-ass, studio-quality mic preamp|
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.
|The picture says it all: notice the Hi-Z input and Lo-Z output|
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!