How to use REW's auto EQ with Equalizer APO

Every filter REW produces is fitted to the room exactly as it was when you measured. Anything you change physically afterwards, a speaker moved 10 cm, a new bass trap, the sofa pushed back, and the filters are fitted to a room that no longer exists. So EQ is the last step, not the first.

1. 1.Settle the speaker and seat positions first. Moving them is free and fixes problems EQ cannot touch.
2. 2.Install Equalizer APO and pick your output device in its Configurator during setup. It only processes the devices you tick there, and it needs a restart before it does anything.
3. 3.Measure each speaker on its own, left and right separately, with the microphone calibration file loaded.
4. 4.Take several measurements around the seat, a few centimetres to half a metre apart, and average them in REW's All SPL graph. EQ fitted to one point fits one point; an average fits the area your head actually moves around in.

• Equaliser: Generic. REW has no Equalizer APO entry, and it does not need one: Generic gives 20 parametric filters, and its text export is exactly the format Equalizer APO reads.
• Target Type: Full Range for speakers used without a subwoofer. Bass Limited if the speaker rolls off in the bass: set LF Cutoff and LF Slope to where and how steeply it actually rolls off, so the EQ does not try to extend it. Subwoofer when you are correcting a subwoofer.
• Room curve or house curve: add a gentle downward tilt rather than aiming for flat. The guide to target curves on this site has a house curve file you can load as it is.
• Target Level: press Calculate target level from response, then look. The target should run through the middle of the measurement, with the peaks you want to cut sitting above it.

• Match Range: from the lowest frequency the speaker plays cleanly up to about 250 Hz. REW's own help recommends keeping filters below 200 Hz or so. Above that, the response changes with every movement of your head, and a filter fitted to it helps one spot and harms the rest.
• Individual Max Boost: 0 dB. Overall Max Boost: 0 dB. Cuts only. This one setting stops REW throwing boosts at boundary nulls and seat nulls, which are cancellations that no amount of boost fills.
• Flatness Target: leave it loose. A lower value makes REW use more filters to hug the target more tightly, and the extra filters go on detail that is different 30 cm away.
• Allow narrow filters below 200 Hz: on when you are EQing an average of several positions, because room resonances really are narrow. Off when you only have a single measurement, or the narrow filters will fit that one point too precisely.

Then press Match Response to Target. The three Optimise buttons are for afterwards: when you have deleted or edited a filter by hand, they refit the remaining ones around the change.

1. 1.Look at the predicted response. The peaks below the match range limit should be down to the target. Dips will still be there, and they should be.
2. 2.Enter the room dimensions in REW's Modal Analysis panel and turn on Show modal frequencies in the Filter Adjust graph. A filter centred near one of the room's modes is doing what EQ is good at. A filter nowhere near a mode deserves a second look at what it is correcting.
3. 3.Count the filters. Five to ten is typical for one speaker in a domestic room. Fifteen or more usually means a single-point measurement or a match range that reaches too high.
4. 4.Compare left and right. The same room produces similar filters on both channels at the modal frequencies. A large filter on one side only often means an asymmetric placement worth fixing physically.

In the EQ window, use Export filter settings as text, once per speaker. Save the files into Equalizer APO's config folder, which in a default installation is C:\Program Files\EqualizerAPO\config. Then open config.txt in that folder, with the Configuration Editor that comes with Equalizer APO or any text editor, and replace its contents with this:

Preamp: 0 dB
Channel: L
Include: rew-left.txt
Channel: R
Include: rew-right.txt

• Include paths are relative to config.txt, so files in the same folder need no path.
• Channel selects which speaker the lines after it apply to. Without it, both files would apply to both channels.
• Preamp stays at 0 dB when every filter is a cut. If you allowed any boost, set it to at least minus the largest boost, so -3 dB for a 3 dB boost, or loud passages will clip.

Each exported line looks like Filter 1: ON PK Fc 48.5 Hz Gain -7.2 dB Q 6.10, which is Equalizer APO's own filter syntax, so nothing needs converting. Equalizer APO picks up the saved file on its own, without a restart.

Now run a new sweep in REW, played through the same output device Equalizer APO is installed on, so the measurement passes through the filters. Compare it with REW's predicted response. They should agree closely below 250 Hz. If they do not, the usual causes are the wrong channel in config.txt, Equalizer APO not enabled on that device, or the microphone in a different place from the original measurement.

Then listen, for longer than one evening. The bass should sound tighter and more even from note to note, without sounding thinner. If it sounds thin, the target is too flat or the match range reaches too high.