Correction Room

[Olivie Inoue]

Ina recent post, we established that the midrange and high-frequency reverb time (RT60), as measured at the listening position in my 4m x 7m Lisbon listening room, clocks in at an average of one second. That amount of reverb, clearly audible in both hand clap and voice recording tests, is far higher than the amount recommended by acoustic professionals: between 0.3 seconds and 0.7 seconds from 300Hz to 4kHz.

I did this then I put a UMIK-1 measurement microphone at the listening position and connected it via USB to an M1 MacBook Pro running Room EQ Wizard (REW) which in turn was USB-connected to the Platin hub. The room correction (RC) curve could be turned on and off with a single click (inside the app) to make light work of taking an RT60 measurement with the room correction off and then on:

The LE version of Dirac Live that ships with the NAD M10 V2 suffers a similar fate. It is hard-curtained at 500Hz to make its correction a bass-only deal. A one-time payment of $99 drops the LE and its 500Hz curtain to give us full frequency response correction (20Hz to 20kHz) and an editable correction curve. I upgraded some years back so up next was a phone call to professional Dirac Live installer Terry Ellis to ensure that no mistakes would creep into the Dirac Live measurement process. The loudspeakers being driven by the NAD integrated were the Zu Soul 6.

However, room correction software appears to have next-to-no control over sounds that have already left the loudspeaker to snooker around the room. How could we reasonably expect anything else? Even if the DSP were to delay some frequencies, they too would reverberate around the room after leaving the loudspeaker (just a little later).

I have experimented with REW (Room EQ Wizard) and room correction, and how to apply it in Roon, and decided to write a guide about it. This is what produced best result for me (I sit in a small room with concrete walls), but the way I did it should work well in bigger rooms and for different walls as well. This guide assumes you have a 2.0 or 2.1 system, and works best if you have a specific listening position and you sit in the middle of the sound, with an equal distance to left and right speaker. By the way, 2.1 systems is measured just like a 2.0 system, with the sub-woofer active during the left/right speaker measurement.

Some of you might wonder why not use the normal way of placing the microphone where your head normally is, and move away while doing the measurement. For me, that way produced a worse result, probably because I sit in a small room and the effect my body and head has on the sound waves becomes relative big. Using sweeps will also give false indications of higher frequencies needed adjustment, due to how short waves the higher frequencies has, and generally speaking a less reliable result. Having said that, if you prefer to use sweeps that do so, both way works.

Updated the guide to generate stereo wav files instead of mono (step 14), if generating mono files I think you also need to write .cfg convolution files, which should not be needed when using stereo wav files (maybe some Roon tech guy an confirm this?).

It must be my lack of tech knowledge, but I get the impression that (this way of) room correction resembles adjusting the EQ (a bit less/more bass, treble etcetera), thus changing the balance the producers and artists have intended. I prefer to hear my music as pure and as close to the way it was recorded. Will room correction improve or deteriorate the original recording balance?

Take the below pics, first is my left speaker and right speaker in my room without any room correction, the last picture is after all adjustments are done (as described in this guide). The sound wave should be close to the blue target line, and I am pretty sure no artists intended it to sound like it does for me without any room corrections (i.e. the first 2 pictures)

Yes, its basically a glorified equalizer, but with very high resolution and ways to decide the steepness of a modification ( the Q value). But unlike old analog equalizers, it works on a digital stream which is handled and modified by Roon in various ways (for example volume leveling), and then converted to an analog signal by your DAC.

Its the data for this equalizer that REW can auto-generate (doing it manually is very hard due to the Q value), and then you can either manually input the data into Roon PEQ or generate wav files for the Roon convolution engine.

Think of the most advanced EQ you can imagine - not only adjusting frequencies throughout the entire audible spectrum (or the parts you specify), but also dealing with reflections (think echos and reverberation from your room).

The easiest mistake to do when doing room correction is if you do one measurement sweep where your head is, and then make REW generate filters from 20 Hz to 20k Hz. Chances are, voices, electric guitars etc will sound very strange after that. The reason for this is that at higher frequency, the sound waves are very short so a few cm difference in measure position might make a big difference, which makes it very easy to overcompensate.

My personal experience (admittedly only using Dirac) is that full range DRC from 20 hz to 20khz can give fantastic results. I understand the reasoning behind limiting to the lower registers, but I think the right software can still deal with the high frequency effectively.

I think that if you modify the higher frequencies smart, which means no sharp modifications (high Q value), it will work. But from a single measurement, its easy to think that a specific small range needs adjustment, for example 1400 - 1700 Hz is 6 dB to high. Modifying that is probably not a good idea, since it probably comes from a faulty reading.

I did measurements and correction in Dirac, which was incredible easy and intuitive. And the result was pretty impressive. I compared to my REW room correction by adding Dirac as its own zone in Roon and playing same tune in both Roon - Dirac and Roon - REW.

Dirac has worked miracles in my setup (difficult room, lots of reflection, bass suckout at listening space). Bass has cleaned up significantly and a bit over overexcitement in the 3000-4000 range has been effectively tempered (my main filter is setup correct up to 4200).

Even though my control room was built and treated specifically for that use, I have always felt there were issues especially in the high end due to reflection off the 6 foot wide splayed live room window to the left of the console/workstation.

Over the last week I did a substantial rework of my control room so that I could switch between 3 pairs of NS10s with a Sub, Truths, and some early 80s JBLs mounted in a soffit as the hyped rock pair within monitor selection within Cubase 10s control room.

While listening to some music from the WDM speakers send on my computer (NOT thru Cubase) I wasnt liking what I heard and found that there was room correction functionality within Windows under properties specific to each set of speaker.

I did a little research and found a suggestion here that said buy IK ARC 2.5 and run it as an insert on the Cubase Control Room Stereo Out (not master buss) so that the correction will feed to monitors but not be applied to exported mix downs.

While Cubase allows you to switch within the software between multiple sets of monitors each feeding the Stereo Out (not master buss) I realized that its a shared insert allowing only for a correction profile for one pair of monitors used when doing the calibrating in ARC.

For those familiar with ARC Is there a way to store and switch between multiple monitor profiles in ARC? while it will suck to have to switch that as well each time I switch monitors via control room buttons, at least it would work correctly.

I`m using arc for years. Define your main output as empty and connect your rme output to control room. Then insert arc as insert effect in the control room Panel on the right side. Your output (Monitors) while be affected by arc, your mixdown not cause it is rooted to the masterbus.

I got no latency difference switching arc on and off.

Update: From what I learned above and on IK forum and conversations with support there are still some issues for using it like cubase control room users would like as ARC saves the last monitors correction used globally, not within the session.

I spoke with support about running multiple instances of ARC in the Cubase Control Room each with their own correction. They told me that it was on roadmap for ARC 3 but they had no target date for release. I expect since it took 6 years to go from 2-2.5 it may be a while.

Thats awesome for you, but for those of us with ARC2 we still do. Then again I havent looked to see if there has been an update since that last posting. Understanding from IK support is that the plugin makes those settings available to save with the session not cubase.

I would like to share with you a young company providing with high quality room audio correction available on Roon.

This is HomeAudioFidelity:

You will find more details about the technology embedded in this solution.

From my point of view, this is the best solution I have implemented so far. Previously I was doing my own corrections using Rew and Rephase but with this solution the results are far more efficient with a very nice soundstage, deep, large and coherent.

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