How to Use Frequency Response Graphs to Improve the Acoustics of Your Room

I still remember the first time I mixed a track that I was proud of – it was terrible, but I had no idea at the time.

The following comes from Sonarworks, a proud partner of DMN (see more on them below).  Author Brad Pack is an award-winning audio engineer and writer based in Chicago, IL.  He currently owns and operates Punchy Kick, a professional mixing and mastering studio that specializes in pop-punk, emo, punk, grunge, and alternative music.  He has been helping artists connect with fans through emotionally resonant mixes, cohesive masters, and insightful guidance for over 10 years.  Check out his website PunchyKick.com or say hi on Instagram @PunchyKick.

I was so excited.

I loaded the song onto my iPod and drove over to my friend’s house, and I could hardly wait to show them my new song. We piled into my tiny car and I cranked the stereo and pressed play.

I was so embarrassed.

The mix didn’t sound anything like it did in my studio! The guitars were flat, the vocals were buried and the drums sounded like someone was hitting a cardboard box with a wet sock. What happened?

I had created a mix that was the sonic inverse of my mixing environment. It may have sounded good in my studio, but it sounded terrible everywhere else. Each time I played my mix on a different system I would hear obvious, glaring mistakes.

I started to doubt my abilities. How could I have missed all these obvious problems? Why would I have made those terrible choices? How did I have ever think this mix was any good in the first place?

Thankfully, I had some great mentors to teach me about translation. Translation means that your mixes that sound good on your system will sound reasonably good on every system. In order to create mixes that translate well, you need to mix on a monitor system with an accurate frequency response curve.

Frequency Response Curves

In a perfect world, professional monitoring systems would be totally flat and accurately reproduce the signal playing from your DAW. In reality, every set of studio monitors in a particular room has a unique frequency response curve, which colors the sound.

Think of it like this — for the most part, we can all agree on what the color red looks like, but no two brands of crayons create the exact same shade of red. Further, the same color may even look different because of the ambient lighting and the writing surface. Studio monitors behave similarly — a speaker system may be flat when measured in a perfect environment, but in a real room and setup, that system will still sound different and perhaps far from flat.

Mixing in an untreated room makes matters even worse.

Frequencies from the studio monitors reflect off of the walls, floor and ceiling and bounce around the room creating reflections and room modes. The size, shape and construction materials of a room will naturally boost certain frequencies and lower other frequencies, and as you move around the room those frequency differences become more or less apparent.  These variations can make it nearly impossible to create an accurate mix.  You may have noticed this type of effect already, for instance when you stand against the back wall of a room the bass is usually much louder than in towards the middle of the room.

Here’s what actually happens during your mix: Let’s say the natural acoustics of your room are creating a 3 dB boost at 120 Hz. While mixing, you’ll be tempted to cut 120 Hz to compensate. As soon as you transfer your mix to another system, you’ll notice the track feels weak at 120 Hz. If you go back to your studio and boost 120 Hz, it just makes the track sound worse and it becomes difficult to find the correct EQ.

So, you start to doubt your abilities and start to wonder why you did this or how you could have missed that. You ask yourself if the mix was ever actually good in the first place, and the cycle repeats.

You’ll never be able to create mixes that you’re happy with if you can’t trust what’s coming out of your speakers.

Instead, you’ll just keep making tracks that sound good in your studio and nowhere else. You’ll keep mixing in circles, trying to EQ your mix to make up for the acoustics of your room.

In order to actually fix these problems once and for all, you’ll need to install some basic acoustic treatment in your studio. That process can be time consuming and a bit expensive, so many engineers start by addressing the biggest problems first and slowly adding more treatment over time. But how do you know which frequencies are causing the biggest problems?

That’s where Sonarworks comes in.

Digital Room Calibration

Digital room calibration software can help you identify and correct frequency response problems in your mixing environment, so you can mix with confidence. While digital room calibration is a very complicated process, the software makes it rather simple. Digital room calibration software allows you to accurately measure the frequency response of your mixing position within the room, then creates a calibration profile based on detected flaws in your listening environment.

Digital room calibration software uses an extremely accurate reference mic with a calibrated frequency response to measure test signals played from your studio monitors. The references tones are sampled at many locations in the room and the software analyzes the way the reference tones are reproduced by your monitors in your room to create a custom frequency response profile.

This frequency response profile is used to generate a corrective EQ curve that is applied to any audio played through the system. This correction effectively adjusts for acoustic problems within the room and also for the specific frequency response of the speakers themselves.

Digital room calibration can also be used to identify frequency response problems within your room and pinpoint the specific areas that need acoustic treatment. By measuring your room again, but with the correction applied, any peaks or dips in the frequency response graph will tell you exactly what kind of acoustic treatment your room needs – if you know what you’re looking for.

Reading Frequency Response Graphs

At first glance, frequency response graphs just look like a bunch of squiggles, but upon closer inspection they can tell you a lot about the acoustic problems in your room. Let’s look at the frequency response curve of this room as an example.

The horizontal axis (from left to right) represents frequencies from 20 Hz – 20 kHz, while the vertical axis represents amplitude, or volume level.

Anything above the black 0 dB line in the center means you’re hearing more of that frequency than there really is, while anything below the line means you’re not hearing enough.

Ideally, you want a flat, neutral frequency response – anything above or below the center line is a problem. As you can see, this room has some pretty serious issues:

  • 6 dB boost, or exaggeration, in the lows around 60 Hz – 100 Hz
  • 9 dB boost in the low-mids around 120 Hz – 400 Hz
  • Various boosts and dips throughout the midrange
  • 6 dB dip around 1 kHz
  • 9 dB dips above 10 kHZ

Based on these results, you can see large problems in the low frequencies, particularly below about 300 Hz.

Those 9 dB boosts would make it almost impossible to correctly mix bass frequencies. Mixing in this room would most likely tempt you to cut WAY too much low-end to compensate for the room, causing the mix to sound weak and thin when played on speaker outside of this room. To correct this issue with acoustic treatment, you’ll need to place bass traps or absorbers in the corners of your room. Placing bass traps in the wall-wall corners behind the monitors typically provides some improvement, and for best results you’ll need to cover as many of corners, from floor to ceiling as possible.

Next, there seem to be a few problems in the midrange, specifically between 400 Hz and 5 kHz.

Unfortunately, in this case, the left and right speakers are presenting different frequency responses — meaning one speaker can sound noticeably different from the other.  This problem becomes more exaggerated as you move around the room and further confuses EQ choices.

These midrange frequency issues are typically caused by “early reflections” from the walls and ceiling points around the mix position, as well as the desk surfaces between the speakers and your listening position. Sound from your monitors travels directly to your ears, and reflections from the walls also arrive a few milliseconds later causing a smearing, or filtering, effect.

This comb filtering results in poor frequency clarity and stereo imaging problems. You can identify these points using “the mirror method,” which only requires a handheld mirror and a little help from a friend. Sit in the listening position while your friend holds the mirror flat against the wall. Have your friend move the mirror around and make note of and spot on the wall where you see a reflection of either speaker. These are the early, or first, reflection points and those spots on the wall should be covered with absorption panels.

Finally, another large issue happens in the high-end, specifically above 10 kHz.

This severe lack of high-end would tempt you to create super-bright mixes that may hurt your ears when played on smaller monitors, like a cell phone speaker. The problem is likely caused by excessive use of absorption panels. A few well-placed acoustic panels are far more helpful than covering your walls entirely in cheap foam, carpet or, heaven forbid, egg cartons that absorb too much of the high frequencies in your room without really treating anything else.

To solve this issue, start by removing any excessive absorption from your room. If you’re experiencing a lack of clarity, try placing diffusion panels at the early reflection points instead of absorption panels. Diffusion panels will disperse the early reflections safely throughout your room, instead of absorbing them. The key is keeping the frequency response relatively flat and that certain frequencies, like only highs, are not removed too much. A typical mix room should only be about 30% to 50% absorptive, while a vocal booth may be closer to 80% or 90% absorptive.

It may feel like a tedious process at times, but each additional piece of acoustic treatment can make your room more accurate and improve your mixing environment.

Just remember to re-measure your room with the calibration applied after installing additional treatment to measure the effects of the treatment. Then use the software to create a new correction curve for use during mixing.

Always keep in mind that electronic room correction, software, like Sonarworks Reference 4, or hardware, like graphic equalizers, will work best when the acoustic issues, like first reflections and bass trapping have been addressed.

To learn more about Reference 4 and try it for free, please visit the Sonarworks website.

About Sonarworks

Sonarworks was founded in 2012 when two music lovers met a scientist and embarked on a mission to deliver the ultimate sound experience for anyone creating or listening to music. The company’s headquarters are based in Riga, Lat and its customers consist of Grammy Award-winning audio and music industry professionals, audiophiles and music lovers around the world.

For more information on Sonarworks, please visit www.sonarworks.com.