Q vs. bandwith

D

drembo

Member
I know that by adjusting the Q, one is adjusting the bandwith. But, how do Q and bandwith exactly relate to each other. What does one unit of Q equal in actual bandwith Hz?
 
drembo said:
I know that by adjusting the Q, one is adjusting the bandwith. But, how do Q and bandwith exactly relate to each other. What does one unit of Q equal in actual bandwith Hz?
Click to expand...
AFIK, this is not a universal standard, but most manufacturers equate the "width" of any given Q setting with the bandwidth covered by the central 3dB of the bell curve of the boost or cut - i.e. the distance between the points on each sde of the cener of the curve where the curve has dropped (or raised, if it's a cut curve) by 3dB.

G.
 
OK, here is my situation. I know I just need to start using parametric EQ and learn from experience. But I have some guide lines I am trying to use as a starting point. For example, if I want to boost "5K-8K, carefully", what does this mean? Start with a one db boost=carefully, and then maybe 2? or 3? What Q would give me a range of from 5K to 8K, when the frequency is set at 6.5K? Is a smaller Q equal to a smaller bandwidth, or is a larger Q equal to a smaller band with. If I wanted to "reduce 200K", what Q would I use, .5 or 10? Or, maybe 1 or 9. What is a functionally useful "narrow bandwidth"? Precisely 200k, and nothing on either side? I am no engineer(although I play one on TV). I don't want to, and hopefully don't need to, re-learn the calculus from my college days just to understand how to use a parametric EQ. Please tell me I don't have to (and really mean it when you say it). And after you tell me that, can you give me some basic tips regarding Q, as a starting point?
 
Just get a parametric EQ that has a good graphic interface that shows the filter curves in relation to the frequency spectrum, then get used to how they sound with different settings. This isn't about understanding math, it's about listening and learning to use a tool.

ReaEQ VST version has a good GUI... it uses octaves to define filter width rather than "Q":
http://reaper.fm/download.php. It's the "ReaPlugs" download, near the bottom of the page.
 
Last edited:
I have a digital work station I use. I don't want to have to buy an outboard EQ so I can understand Q, and I can't use plug-ins.
 
Divide the center frequency by the total bandwidth you want to affect and that is the Q. The outer edge of the bandwidth will be half the volume, or 3db, less then the center frequency.

In your example it's 6500/3000 = 2.17

A Q of 2.17 will put you in the ballpark then use your ears from there.
 
It just came to me that electronic theory and music theory have in common the fact that , while it can be very handy to have the knowledge, there is no substitute for a great set of ears and a backlog of experience when it comes to writing , arranging, tracking, mixing and mastering.


chazba
 
drembo said:
...some basic tips regarding Q, as a starting point?
Click to expand...
OK, some basics... A bell filter with Q of 1 is fairly wide, a good starting point for a natural sounding boost or cut. Q of .5 is wider still. A 1 or 2 dB change with a Q of 1 or less will usually sound very natural. Q of 2 is narrower. IME the more narrow the filter's curve, the more artificial-sounding its effect will usually be. I rarely use a filter that's narrower than Q2 but many do.

The amount of actual change in the sound, with the same settings, varies a lot from one EQ to another. I have EQ's that make a huge impact on the tone with a fairly wide 1 dB change, and others that don't. And some EQ's sound veiled regardless of how you use them, while some sound clean and clear. Both are reasons why one can really only learn about EQs by using them.
 
If you wnt to make a bosst or cut in a certain region only, the Q will change as your gain changes. at a 1db boost, it will take a certain Q to boost a certain frequency range. At a 2db bosst though it will take a narrower Q to only affect the same range.
 
drembo said:
I have some guide lines I am trying to use as a starting point. For example, if I want to boost "5K-8K, carefully", what does this mean? Start with a one db boost=carefully, and then maybe 2? or 3? What Q would give me a range of from 5K to 8K, when the frequency is set at 6.5K?
Click to expand...
I don't think it means "boost all the frequencies between 5k-8k". But rather means, the center frequency for your parametric EQ should be somewhere between those frequences. Which frequency should it reall be on? That's where you need to judge it by listening to the material at hand. First off, what is your goal that you want to accomplish by boosting somewhere between 5k-8k? Next, does your material need that boost? If so, the next question then probably is "How do I find that center frequency?". To find where you need the center frequency, start with high Q (meaning a narrow Q), boost some and sweep the EQ between those frequencies while listening. Once you find the area where you get the characteristic you're after, then probably you'll need to lower the boost and widen the Q, again using your ears. In general wider Q tends to sound more natural, while narrow Q is great for targeting specific bothersome resonances (for example) and eliminating or minimizing them.
 
You must log in or register to reply here.
Back
Top