Understanding and Preventing Comb Filters | Live Sound Basics
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- Опубліковано 12 лип 2024
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We often blame comb filters for many of our audio woes, but do you understand what’s going on under the hood?
What most engineers describe as a hollow, “phasey” sound is the telltale sign of comb filtering. How can we use discerning ears to find it and the right tools to prevent it?
We’ll cover:
- Why you can’t fix comb filtering with EQ
- What’s the predictable patterns comb filters have?
- How to run your own experiment and analyze comb filters yourself
00:00 - Intro
01:08 - Physics of Sound Basics
04:56 - What is a Comb Filter?
13:10 - What does a Comb Filter Sound Like?
14:08 - Creating and Analyzing Comb Filters
17:38 - How can we prevent Comb Filters?
I love your balance on learning vs application.
Very much appreciated.
Love it! This is a very big deal in indoor zones, as well as multiple speakers with the same signal potentially interfering with one another. This is why i like to have a slight stereo pan on outside music. This of course depends on the setup but being able to have slight differences in the sound coming from two speakers helps a bunch with comb filtering.
This has been the one downside to mono systems I have found to be honest. Comb filtering the same signal from the top speakers. You can see this in Ease Focus when looking at a small octave frequency. very slight comb filtering with the same exact signal.
LOVE your stuff, Michael. You are a great educator and love the information you spread.
Thanks a ton, Colin!
Fantastic explanation and demonstrations. Great video - I learned a lot.
Glad it was helpful!
This couldn't have come at a better time. I have just started mixing at a church where the pastor asked me last Sunday what that sound was he heard when he walked from the back of the sanctuary to the front at the start of the service. I asked him what it sounded like and he made a sound like WWAAAaaooaaAAAA. I played some music and he and I walked the same path as at the beginning of the service, back to front, we both heard the very sound you demonstrated with your ipad! I told him I knew what it was and I would look into it but didn't know how I could rectify it. Your video popped up while doing the research. I love the way you can take such complex concepts and make them understandable.
Hey, David! So glad you were able to stumble upon my video. Yes, comb filtering due to the floor bounce was exactly what you were hearing.
So how did you remedy this?
Excellent 🎉 very clear man! Congrats
Thank you!
Great job sir
Thank you!
Great advice about PA placement and delta reduction--I'm going to keep this in mind. Also, it's interesting how the phase wheel diagram looks exactly like a cardioid polar pattern.
Isn't that a wonderful graphic from Merlijn Van Veen? I never made that connection to the phase wheel and cardioid patterns until I saw that graphic.
Some good info here
Thank you!
Thank you for the wonderful explanation and the demo ! Btw, do you build the obsorb panels by yourself ?
You're very welcome! No I did not build these. I got them from GIK Acoustics. But in my next studio space I plan on building them out.
Cool ! Can’t wait to see 🤟🤟🤟
Thank you for this video!
What I've never understood, is it always the same frequencies no matter what is playing out of the speakers? So if there's a 1ms delay on ex. both a singer/songwriter concert, as well as a heavy punk concert, will the comb filtering still start at 500hz on both of them?
Sorry if you already explained this in the video, and I just didn't catch it
Finally someone who actually gets into the nitty gritty of it! Thank you so much! Question though - If you have two sin waves of the same frequency set at a constant offset, wouldnt they always retain a constant relative offset between their phase points? In order for them to go through a full 360° phase cycle relative to eachother wouldnt one have to be either increasing or decreasing in frequency? I will pay you if you will talk more about this with me over the phone for 30m
Great question Ethan! The original phase offset could either be due to a static full-bandwidth time offset, or a gradual timing offset over frequency.
In your case, you're talking about a single sine wave - so either of the above changes would have the same result.
A 1kHz sine wave has a period of 1ms, so delaying it by 1ms would mean 360° of phase shift. Another 1kHz would still be turning at the same rate of 1kHz, but if it was not delayed it would retain its original timing, and therefore phase, relationship to the other delayed 1kHz sine wave.
@MichaelCurtisAudio Thanks! After days of thinking about it it all finally clicked. So cool to be able to calculate how any specific delay time will create interference across the frequency range! And gives some really interesting compositional ideas too about using flangers with very precise intent to emphasize or deemphasize certain frequencies or even chords within a key or section of a piece!
I was just thinking about this the other day. I was thinking about getting some new PA speakers. One option is a pair of boutique passive speakers that go down 30 Hz and can handle 800W RMS. I thought maybe I could use these instead of satellites over subs. Would having the low frequencies apart like that be just as bad as having subs on each side of the stage? I think it would right? Isn't that "power alley" effect a type of comb filtering? Would running 15" full range tops on sticks sound worse than using high-passed tops with a central sub simply because of comb filtering of the low frequencies?
I wouldn't say that one setup is inherently better than the other, but there's a different set of tradeoffs depending on the system you choose. Having audio sources coupled (close to together) helps eliminate the comb filtering effects, like you said. So, you can either choose to have your mains and subs coupled, or all of your subs coupled.
In smaller format ground stacked systems I typically prefer a center sub setup with my mains on sticks, then using crossover appropriately to divide up the low end.
Hi is it ideal to separate the vocal signal and the instrument signal from mainLR?
For example I have 2 left and 2 right front speakers.
If you're frequently mixing in venues with bands that have a lot of stage volume it's common to matrix out your band group vs your vocal group. You may need more vocals in your front fills that the band since you're getting amps/drums from the stage.
Too bad I’ll never even be 1/8 of knowledge into speakers and sound that way. All I heard through the whole video was htdbmpitbfsw3gumkonytcdsst7j That’s the language you might as well have been speaking lol. The funny thing is the comb filtering still sounded great to me, it was like a vocal effect being applied. I’ll let myself out now lol
Any skill you want to possess can be cultivated, do not deem yourself done for. You can learn about anything you want as long as you put some time into it
+1 to that!
Thanks Michael,
How would you make a single mic on guitar amp into a stereo image, some say you should copy the input to a second channel and then PAN them hard LR, then delay the one channel for that wide sound. Is this not just creating comb filtering?
You're exactly right. This technique is often used more in studio contexts, but it's used in live settings as well. The problem using it live is that the perceived separation it offer only applies to the listener directly in the center of the speakers. If you take one step to the left or right your own physical location now provides the time offset to the left or right speaker, as well as a level change that then results in an imaging change.
In my opinion that technique does not translate well to a live context at all, and I only do it in a studio context after applying other heavy processing to the duplicate channel to decorrelate it from the original signal. Dan Worrall and Fab Filter did a great series on this - ua-cam.com/video/spaqBr-cCFw/v-deo.html
@@MichaelCurtisAudio It would be great to work for you for a year and just learn, South Africa is a bit far unfortunately.
Atleast i can learn from these videos. Thanks Michael.
If you ever get a trip over to the states and get to do some gigs let me know!
also when you see people put multiples of the same cab hitting the same area side by side without concideration of their dispersion
But more is more, right : )? All jokes aside, I used to make that same mistake.
Please can you me how to send drum buss into the DAW
Your console needs a digital output. Then your route all your drums to a subgroup, then route that subgroup to a digital out that's picked up in your DAW.
Hey what’s the best email to contact you ?
It's on my website homepage at the bottom.