- What is room calibration software?
- We put Sonarworks Reference 4 to the test
- Can Sonarworks Reference 4 replace acoustic treatment?
Sonarworks Reference 4 Review
To preface this article and satisfy the TL;DR readers of you out there, here’s my take:
I use Sonarworks Reference 4 in every session. I find it improves my accuracy and how well my mixes translate. It has been a welcomed tool.
That being said, there are a lot of nuances and things to take into consideration. Read on, as in this article, I’ll go into detail about my experiences with Reference 4: the positives, the negatives and everything in between.
Why Use Room Calibration?
Though it doesn’t often receive attention, the environment plays a critical role in how accurately we hear.
This is because our rooms add resonances and reflections influencing sound. This occurs for both the mixing engineer and the average music enthusiast in their bedroom.
It is, therefore, necessary to consider room acoustics in any recording, music, or critical listening environment.
Before the days of advanced digital signal processing (DSP), room acoustics could only be altered by changing physical elements within a space.
However, acoustic calibration software claims to challenge that and has grown in popularity with the increase in computer processing power.
Such software aims to improve sonics and the accuracy of what we hear by applying an equalizing correction factor to the speakers, and or headphones, we listen to.
The correction factor is supposed to remove unwanted colorations so that we are listening to a neutral flat frequency response. This sonic perfection then translates to… well mixes that translate.
The most common unwanted colorations are:
- A non-linear frequency response – This makes it difficult to hear music accurately and choose appropriate mix decisions.
- Uneven decay times – This can cause masking of the higher-frequencies and an unnatural non-musical sound to the room.
- Prevalent early reflections – These can distort imaging and cause considerable comb-filtering.
There are many professionals that attest to the efficacy of such software. There are also purists who stay away from digital correction factors indicating that they impart phase distortions causing more harm than good.
There remains a certain level of skepticism and uncertainty even though calibration software continues to grow in popularity.
Here are some common questions regarding room calibration software:
- How do you calibrate your room?
- To what extent can such software improve a room’s acoustics?
- Does it take the place of acoustic treatment?
This article aims to review a popular room correction software, Sonarworks Reference 4, and in doing so shed light on these questions. If you simply can not wait, skip ahead to the summary below.
An Introduction To Reference 4 & Calibration
This article will focus on the effects Sonarworks Reference 4 (find out the latest price on PluginBoutique) has on the most common studio monitoring setup, i.e. a stereo pair of near-field studio monitors.
You can also apply a correction factor to headphones. This is as simple as selecting your model from their 200 plus profiles. For a thorough look at headphone calibration and its benefits, see Headphone Calibration Software: Worth It, Or Hyped Up Junk? by Peter Dimou.
Calibrating your system with Sonarworks Reference 4 is very easy. Their graphic user interface (GUI) is user friendly, entertaining, and it prompts you throughout the entire process.
Therefore, you do not need to have extensive knowledge to perform the calibration. As a benefit, the software serves as a decent educational tool, introducing the basics of acoustic calibration.
Yes, You Need a Reference Microphone
You will need a specified reference microphone to accurately and reliably record your rooms’ sound or “color”.
These microphones are designed to have a linear frequency response, low total harmonic distortion, and an omnidirectional polar pattern. Standard studio microphones, such as a Shure SM57, will simply not cut it.
While there is a vast array of reference microphones, the humble Behringer ECM 8000 is a common choice due to its accuracy and affordability.
Ethan Winer of RealTraps, an acoustics manufacturing company, compared professional reference level microphones to more affordable options. The article can be read here, and results concluded that inexpensive options can be plenty adequate.
Some calibration microphones, such as the Sonarworks XREF20, come with a calibration file from the factory. This can further improve the accuracy of your measurements by removing any colorations imparted by the microphones’ own frequency response.
Calibrating Sonarworks 4
The basic process of calibration is as follows:
- After installation, Sonarworks will take some preliminary recordings. Here you will be moving the reference microphone to triangulate your listening position and measure the noise floor.
- Sonarworks then prompts you through a 37-point calibration where you move the microphone at and around your listening position. With each recording, the software gathers acoustical variances improving the accuracy of its correction factor.
- Once the calibration is completed, you can enable the correction factor and adjust parameters such as bass-tilt, wet/dry mix, and target curves.
- You can choose to apply your Sonarworks correction factor to all computer output through their Systemwide application. It can also be applied within your digital audio workstation (DAW) by adding the plug-in to the last insert of your master fader.
For a more thorough walk-through, you can read Sonarworks’ description here.
Reference 4: Theory vs Practise
Let’s move beyond the theoretical and see what Sonarworks Reference 4 looks like in my recording space.
Once calibration is completed, Reference 4 software displays the measured response for my left and right speakers. Enabling the software applies the correction factor and a new simulated speaker response is visible.
This represents the theoretical speaker output after the calibration factor is applied and it more closely matches the desired linear flat line (see Figure 1).
If we go by the simulated speaker output, we assume our sound system has a nearly flat, or linear, response above any low-frequency roll-off.
This would be fantastic; however, it is just a simulated output of the speakers. It is not how the room responds at your listening position to the new speaker output.
In order to understand the actual effect of Reference 4, we need to compare the room response from the listening position with and without the correction factor enabled.
This gives us a point of comparison and includes the physical space we are listening in.
Room EQ Wizard (REW) was used for all tests performed below and measurements were calibrated to +/- .5 dB using 70 dB A-weighting broadband stimuli.
The frequency sweep was routed from REW to
Here are three basic areas where we will put Sonarworks Reference 4 to the test:
- Frequency Response – Like speakers and microphones, we can capture a snapshot of how our room responds across the spectrum. This graph will help show how the correction factor combats my room’s natural frequency response. Ultimately, we will see if it helps me approach that sought-after linearity.
- Waterfall Graph – This graph gives excellent information regarding how a room responds over time. By looking at decay times, we will see my room’s resonances and reverberations and can, therefore, evaluate how Reference 4 influences the decay of different frequencies.
- Energy-Time Curve – Energy-Time Curves (ETC) are another time-domain measurement assessing the overall frequency energy after an impulse. By looking at an ETC graph, we will see how Sonarworks Reference 4 affects early reflections as measured at my listening position.
These are very common acoustic measures for checking control rooms. Therefore, by performing A/B comparisons we should gain insights as to what benefits, if any, Reference 4 has to offer a treated studio space using near-field monitors.
Check 1: Frequency Response
Our first step in this experiment is to look at a frequency response graph. This is the same graphic found within Sonarworks Reference 4 software (see Figure 1 above).
A frequency response graph is generated by presenting a stimulus into a room and recording the room’s response to it. This commonly involves a broad frequency sweep and multiple measurement points.
The resulting graph shows us whether the room is accentuating or decreasing acoustic energy, at any given frequency, at the area we measured. Think of it as a snapshot overview of your room’s “color”.
Figure 4 displays the frequency response of my studio with and without Sonarworks Reference 4 enabled.
The red line shows my room’s normal response while the green line indicates how Sonarworks Reference 4 is altering the sonics.
This graph is very revealing as it shows that the room response, post-correction factor, is not flat or linear as displayed in the Reference 4 GUI. This illustrates the difference between a simulated speaker output and a real-world measurement.
So, what can we make of this? Ideally, we would want my room’s frequency response to be as close to a flat 70 dB line as possible.
This would indicate little to no coloration from my room. The green line, which represents my room response with Sonarworks Reference 4, is much closer to that expectation. The only exceptions being at either extreme of the spectrum.
Therefore, the software has seemed to improve the linearity of my room’s frequency response.
More seasoned readers may note that 1/3 octave band smoothing was used which can artificially improve the appearance of a room’s frequency response.
While this is true, the smoothing was applied to reduce complexity and improve comprehension for the average viewer.
Furthermore, it better illustrates that the correction factor appears to, on average, improve linearity.
Check 2: Decay Time Waterfall
Frequency response graphs provide great insights as to how a room responds to sound. However, they neglect some very crucial elements. Sound, by definition, is our perception of pressure changes in the air over time.
Therefore, it is important for us to consider how our room responds to sound over time. This is where waterfall graphs come into play.
It still gives us the frequency and amplitude along the x and y-axis, respectively. However, we can also view time on the z-axis. These time-domain graphs can be very intimidating if you are new to them, so do not be discouraged if they are difficult to make sense of.
We are simply looking at a series of frequency response graphs stacked back-to-back over time. Waterfall graphs are, therefore, very useful when assessing resonances and reverberations within a space.
In Figure 5 we see my room’s normal decay time waterfall graph towards the left.
The overall curvature should look familiar as it is identical at time “zero” (or at the very back of the graph) to the frequency response graph above.
Looking at my room’s normal response, we see it extend significantly on the z-axis around roughly 33 Hz, 40 Hz, and 76 Hz.
These regions are circled in red. This is a result of room modes and is commonly referred to as “ringing”. This means that my room has strong resonances at around 33 Hz, 40 Hz and a slightly less prevalent resonance roughly an octave higher at 76 Hz.
Ideally, a waterfall graph would show near equal decay times. For example, control rooms normally aim for decay times of roughly .4 seconds across the audible spectrum.
Uneven decay times can amount to a room sounding unnatural and higher frequency sounds being masked by the lower “ringing” resonances.
In both graphs above, we see the same strong low-frequency resonances with only minor changes.
This makes sense as Sonarworks Reference 4 is only altering the presentation levels of certain frequencies; however, it is important to note that these resonances are not removed by the software.
This is logical. No amount of equalization can change the absorptive properties of the surfaces in your room.
Check 3: Energy-Time Curve (ETC)
ETC graphs are like waterfall graphs as they consider sound over time. However, we take a broader look at acoustic energy so that we can assess reflections within the room.
We are specifically looking at the early reflections that arise from surfaces like our side walls, front wall, ceiling, floor, and computer desk. These reflections commonly arrive at your listening position within 35 milliseconds.
This time range is important as it defines where reflections are temporally-fused or smeared, to be perceived as one sound as opposed to discrete reflections like an echo. Search Haas Effect if this concept piques your interest.
It is important to consider these early reflections as they influence imaging and cause coloration due to constructive and destructive interference (i.e. comb-filtering).
Reflections are not inherently bad though as they reinforce the direct signal making sources sound natural and more musical. In fact, if we remove too many reflections our rooms sound very unnatural.
Our goal with ETC graphs is to monitor the following:
- Reflections are hopefully at least 10 dB less than the initial stimuli.
- Each consecutive reflection in time is ideally quieter than the preceding reflections.
- ETC graphs from all speakers show similar tracings.
If Sonarworks Reference 4 is to pass this check, we should see an improvement in some of these areas. In Figure 6 below, we see an ETC graph generated from my listening position.
Three pronounced reflections are present (circled in red) following the peak at time zero which is the initial stimulus.
The ETC graphs above are nearly identical displaying early reflections at roughly 2, 4.2, and 18.2 milliseconds.
A slight decrease in amplitude is noted at the 2-millisecond reflection. Like the waterfall graphs, the slight change in amplitude can be attributed to the correction factor altering the presentation level of certain frequency ranges.
However, all three reflections remain present.
Sonarworks Reference 4 does consider the distance between each speaker and the listening position during calibration.
Therefore, it is possible for Reference 4 to improve the accuracy of the phantom center. However, these ETC graphs show that the early reflections were not removed from my studio.
Let’s Summarize & Tie It Altogether
There is considerable subjectivity surrounding our gear as audio engineers and musicians. We are often left to anecdotes and forum arguments to parse what gear will best suit us.
It can be exhausting. Even when we do our best to research, we can have no clear answer to our “this microphone” or “that speaker” questions.
Hopefully, this article demystifies some of the uncertainty around correction factors. We performed the most common measurements to check the accuracy of a control room.
Therefore, we can objectively comment on the benefits this correction factor offered in my studio through the A/B comparison. Let’s summarize what we found:
- The frequency response test suggested that the correction factor from Sonarworks Reference 4 improved the linearity of my listening position. That is, overall deviation from the desired flat 70 dB response improved other than at extremes of the spectrum.
- The waterfall graphs suggested no improvements in modal regions. In fact, the correction factor resulted in a roughly 2 dB increase at 40 Hz further exciting the fundamental resonance.
- The ETC graphs indicated that the correction factor from Sonarworks Reference 4 had little to no effect on early reflections. Further, it was obviously not able to remove them.
This summary is not entirely surprising. A correction factor applied to the electrical output of the computer and DAW will neither affect the absorptive qualities of a physical space nor remove the resonances within that space.
We can state that software like Sonarworks Reference 4 can influence monitoring in the frequency domain. However, they do not influence it in the time-domain.
Can Calibration Software Replace Good Acoustic Treatment?
At this point, it should be clear that correction factors are not acoustic treatment. Acoustic treatment alters the way a room responds to sound.
Correction factors change the output of your speakers and headphones. When we define them, they are obviously two very different things.
Appropriate acoustic treatment will always offer more than corrective software.
So, when is it appropriate to use plug-ins like Sonarworks for your speakers?
I highly recommend you start with acoustic treatment, educate yourself as much as possible, and improve your rooms’ acoustics from a physical standpoint.
There are plenty of great references online. Here is an article teaching you how to optimize placement and positioning of acoustic treatment within a room.
Once you have exhausted this option, correction factors may help take it a step further.
The purpose of this experiment was not to tarnish or refute the benefits of such software. Rather, the aim was to define the benefits. That way, users are better informed and can get the most out of their studios.
Sonarworks Reference 4 offers regular sales, educational discounts, and even a free trial. That means you can try the software and hear what it has to offer with your own ears!
Honestly, my chief complaint with Sonarworks is that it’s hard to remember to disengage when bouncing down/printing my final sessions.
So yes, I do use Sonarworks Reference 4 in every session. It improves my accuracy and how well my mixes translate. It has been a welcomed tool.
As with all gear and techniques in the studio, take the time every few weeks to think critically about your engineering choices.
Does this help improve creativity, efficiency, mix quality? You can always switch out a tool if that answer is no. Audio and acoustics is an experimental process, so keep doing anything that drives your creativity and gets your ears between the speakers.