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Frequency masking


alexclaber

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I thought I'd start a thread on this because it's the main bugbear that we bassists suffer when trying to be heard at gigs or on recordings. It's also another reason why that great tone you EQ'd in whilst the band was setting up can't be heard once the guitarist starts playing.

 

From Wilkepedia:

 

"Masking effects:

 

In some situations an otherwise clearly audible sound can be masked by another sound. For example, conversation at a bus stop can be completely impossible if a loud bus is driving past. This phenomenon is called masking. A weaker sound is masked if it is made inaudible in the presence of a louder sound.

 

If two sounds occur simultaneously and one is masked by the other, this is referred to as simultaneous masking. A sound close in frequency to the louder sound is more easily masked than if it is far apart in frequency. For this reason, simultaneous masking is also sometimes called frequency masking. The tonality of a sound partially determines its ability to mask other sounds. A sinusoidal masker, for example, requires a higher intensity to mask a noise-like maskee than a loud noise-like masker does to mask a sinusoid. Computer models which calculate the masking caused by sounds must therefore classify their individual spectral peaks according to their tonality.

 

Similarly, a weak sound emitted soon after the end of a louder sound is masked by the louder sound. In fact, even a weak sound just before a louder sound can be masked by the louder sound. These two effects are called forward and backward temporal masking, respectively."

 

Notice that a noise-like maskee causes much worse masking effects than a sinuisoidal one. Undistorted instruments lie somewhere between the two types and therefore can cause fairly challenging problems. Distorted instruments (i.e. rock guitar) are much more noise-like and therefore really raise the threshold of audibility for the other instruments.

 

Here's a graph of threshold of audibility in a quiet environment (notice how much louder bass sounds have to be to be heard):

 

http://www.liacs.nl/~joostd/WebTech/Day6/slides/images/7-58a.jpg

 

Now here's a graph where a masking signal has got involved. This masking signal is at the fundamental frequency of the 7th fret E on the A-string of a guitar, or alternatively the second harmonic of the open low E on a guitar. In layman's terms, this graph shows the low frequency masking causes by a typical guitar signal, but underestimates the effects of all the overtones present in the guitar sound.:

 

http://www.liacs.nl/~joostd/WebTech/Day6/slides/images/7-58b.jpg

 

See how this really raises the threshold of audibility for our bass sound?

 

What's the solution? Firstly, get the guitarist to keep their volume under control because this frequency masking doesn't just affect lower instruments like the bass, it also hurts higher instruments like the voice.

 

Secondly, try and avoid big speaker cabs, large speakers and/or sealed and even worse, bass reflex cabs, for guitar. All this contribute to the guitar's low frequency output, and the more it puts out in the 150Hz region, the more we suffer in the 30-150Hz region, as well as in our fundamental midrange area (from 250-800Hz).

 

Thirdly, leave your EQ flat until the whole band is playing, then make subtle tweaks to dial in a sound that lifts you above the threshold of audibility without having to crank the volume and thus cause the masking problems for everyone else (so they have to turn up, which masks you; so you have to turn up which masks them; and then you run out of power and start to go deaf...)

 

Useful?

 

Alex

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Useful for those who understand it.

 

Even those who understand it (and aren't more concerned with the power/ego-trip of playing loud :rolleyes: - "look at me! I'm not really a powerless drone!"), there's still the little issue of the drummer setting the "minimum" volume.

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Yes, but isn't it usually the g*****ists that drone out the bass. Spending time experimenting with the EQs of bass and guitar would be very useful. I note that an acoustic guitar masks the sound of the bass much less. Davo
"We will make you bob your head whether you want to or not". - David Sisk
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Originally posted by Davo-London:

Yes, but isn't it usually the g*****ists that drone out the bass. Spending time experimenting with the EQs of bass and guitar would be very useful. I note that an acoustic guitar masks the sound of the bass much less. Davo

I did make those points, but obviously not terribly eloquently!

 

i.e. Regarding guitarists being the usual problem, the second graph showed the effect of a guitar range masking signal:

 

"This masking signal is at the fundamental frequency of the 7th fret E on the A-string of a guitar, or alternatively the second harmonic of the open low E on a guitar. In layman's terms, this graph shows the low frequency masking causes by a typical guitar signal, but underestimates the effects of all the overtones present in the guitar sound... ...See how this really raises the threshold of audibility for our bass sound?"

 

And regarding clean/acoustic vs distorted guitar:

 

"Notice that a noise-like maskee causes much worse masking effects than a sinuisoidal one. Undistorted instruments lie somewhere between the two types and therefore can cause fairly challenging problems. Distorted instruments (i.e. rock guitar) are much more noise-like and therefore really raise the threshold of audibility for the other instruments."

 

It is rather techy, but it should make sense if you understand things like decibels (SPL), hertz (frequency) and what sinusoidal (pure but unmusical single frequency tone) and noise-like (totally fuzzed out wide band i.e. multiple frequency, tone) sounds are.

 

And on re-reading, to clarify this: "Secondly, try and avoid big speaker cabs, large speakers and/or sealed and even worse, bass reflex cabs, for guitar." That's TRY AND STOP YOUR GUITARISTS USING STACKS OF 4x12" CABS (or even worse, ported Randall cabs a la Dimebag (RIP)). For bass, definitely use as many large bass reflex cabs as possible to get clean undistorted lows, to avoid competing with the guitarist's bit of the spectrum.

 

The way I tend to approach these things, particularly when recording, is to make the instruments as different as possible. So ideally, I'd rather the guitar be through a small open-backed valve combo, to minimise the LF output, and miced with a farily midrangey mic like an SM57. I tend to DI the bass, but if the cab is miced I use a different type of mic to the one on the bass drum, so again, they carve out their own bit of the sonic spectrum. Likewise, if the guitar amp and snare are both through SM57s, I'd want to vocals to be through a differently voiced mic, preferably a large diaphragm condenser. Etc.

 

All this helps each instrument find it's spot in the mix, without masking each other too badly. And if the sounds are sufficiently diverse before the mics gets involved, then you have a huge headstart for clear yet fat sound, either live or in the studio.

 

Alex

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I think people with recording experience are much more likely to acknowledge this issue. In recording, everything is "mixed" into a single signal in the end (headphones or speakers). The issues you raise become very important.

 

What's not so obvious is that something similar happens in the air. "Common sense", while wrong, might suggest that an "amp here", an "amp way over there", and a "drumset up there" shouldn't interfere. In reality, the vibrations in the air interact in much the same way that electronic signals in a mixer do. More experienced players have noticed this, and refer to issues re: "cutting through the mix".

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That article explains a lot! I've always wondered why I could sometimes cut through and sometimes not, regardless of the EQ. I also assume that the acoustics of the room can play into the masking effect as well?

Tenstrum

 

"Paranoid? Probably. But just because you're paranoid doesn't mean there isn't an invisible demon about to eat your face."

Harry Dresden, Storm Front

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Very interesting. Appreciate the research you put into this. :thu:

I might use this at a party this weekend with some guitar players as one of them's got an engineering degree from Berklee College of Music (Boston metro area of MA, USA) and might be one of two people at the party who'd be able to intelligently discuss this besides moi. The other is a sound engineer (he's a licensed architect who does pro sound and plays occasional guitar on the side) who's hosting the party. If I get any interesting insights from them I'll be sure to post them.

 

Question: do you think where the EQ takes place (onboard the instrument, at the first preamp stage, at the FX loop) makes a difference in reducing F-masking?

 

Meantime, I'll just make sure my amp has 2-4 times as much output as the collective output of the guitar amps at the party. I know it won't solve the EQ problem but it's sure to aggravate them if they decide to crank their Marshall stacks to 11!

:D

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Originally posted by C. Alexander Claber:

All this contribute to the guitar's low frequency output, and the more it puts out in the 150Hz region, the more we suffer in the 30-150Hz region, as well as in our fundamental midrange area (from 250-800Hz).

Useful?

 

Very useful and also fascinating! Thank you for posting this.

 

Would you (or anybody) happen to have a chart (or raw data) on frequency outputs for the various instruments (bass, drums, guitar, vox, keys) in a typical rock band?

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This is my pet peeve about "dialing in" a sound individually. A great tone means NOTHING if you haven't played it with your ensemble. Taking up the entire frequency spectrum with your instrument just leads to extremely large headaches for either the audience or the engineer.

 

But this is also an issue that needs to be examined by extended range bassists (or any bassists for that matter). Are your full range cabs playing havoc with the keyboard player? Is your 20" sub making the kcik drum inaudible?

 

As a keyboard player, I always have to be careful that the sounds I choose are not masking (or doubling) the rages put out by bandmates. The piano sound I noodle on at home is MUCH fuller than the one I'd use in a gig.

 

Can't we all just get along?

"For instance" is not proof.

 

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Originally posted by Matt W:

I'm posting it on the bathroom door, so my wife understands that it does no good to talk to me when the water is running.

:D:D So true !!

 

I'm finding that lots of noises mask my ability to hear conversation (fridge motor, microwave, etc.). It seems to be getting worse as I get older.

 

Alex - there is one solution offered by the write-up that hasn't been explored. Since distorted sounds have a greater ability to block, it's even more important to limit guitar frequencies when they are distorted.

 

Or we should just step on our own distortion and blow those folks into next Tuesday !!!

 

In my current band I suffer more from the keys blocking me than the guitar. Am considering an arm sling for his left arm.

 

Tom

www.stoneflyrocks.com

Acoustic Color

 

Be practical as well as generous in your ideals. Keep your eyes on the stars and keep your feet on the ground. - Theodore Roosevelt

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Originally posted by Tom Capasso:

 

In my current band I suffer more from the keys blocking me than the guitar. Am considering an arm sling for his left arm.

 

Tom

Hey Tom:

I didn't realize you worked with the same keyboardist as I do! Surely there's not more than one like that?

...and it's not even blocking/masking - it's also conflicting notes.

argghhhh!!!

 

I thought we had the problem licked when synth manufacturers added those Mod/Pitch bend wheels!!!

Suddenly, every keyboardists' left hand was busy doing bends and such.

 

Counted my chickens too soon...

 

Jim

Jim

Confirmed RoscoeHead

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