In some cases it's not possible to do the full measurement and EQ method described in the app note Headphone EQ with EARS and REW. For example, when doing EQ on a phone, tablet, or portable DAP (digital audio player), there is no direct way to send the measurement signal from REW through the audio device.
You can still use EARS to measure and EQ your headphones though. In this app note, we'll walk through two ways of doing this. The first is easier, the second is more accurate.
A note on SPL calibration. If you have previously set the REW SPL calibration for your EARS using the procedure in the EARS User Manual, there is no need to calibrate SPL again. Otherwise, where this application note suggests setting the SPL to 80–84 dB, just listen and set volume to a moderate level.
Implementing EQ
You will need a way to implement the EQ. We used the free Sennheiser CapTune app, which is available for iOS and Android. (You can use it with any headphones, not just Sennheisers.) The user interface takes some getting used to and the EQ screen is a bit tricky to use, but it has the big advantage that it can stream Tidal as well as playing music files from the phone or tablet.
If using a DAP, many have built-in EQ of some form. Ideally, it will have some form of parametric EQ (variable center frequency and bandwidth as well as gain), but even a graphic EQ can be used if that's what you have.
Method 1: Pink noise and RTA
In this method, play pink noise through your phone while monitoring the spectrum of the headphone (via EARS) using REW's RTA function. You can then adjust your EQ in real time.
The downside of this method is that pink noise RTA has no noise immunity. So any external noises will be picked up by the EARS, especially in the bass. You will want to do this in as quiet a location as possible, but remember that even distant traffic noise may affect the lowest frequencies.
To start with, generate a pink noise file using REW's Signal Generator. Use the settings shown in the screenshot below, in particular making sure that "Full range" is selected. Click on the WAV button and then OK in the second box that pops up to save the file as "PinkNoise.wav". (It doesn't matter which channel you set for "Output," pink noise will be written to both channels of the file.)
Load this file onto your phone or DAP, using whatever method you normally use. If using iTunes on a Mac, for example, open the WAV file in iTunes and then connect and sync your phone. For other phones or DAPs, you can probably just drag and drop the file to copy it over.
Start the CapTune app and locate PinkNoise.wav by going to Audio Sources, then Local Library then Songs. Click to play it, and set the "repeat single track" button on. The file is a minute long, so this saves having to keep restarting it while adjusting EQ. Then stop playback.
Position your headphones on the EARS. On REW's Preferences screen, select EARS as the input source. It doesn't really matter whether you select Left or Right channel input. On the Mic/Meter tab, load the HEQ calibration file for the selected channel:
Click the RTA button to open the RTA window and set the control parameters as shown in the next screenshot. You can vary these if you wish, but we found this to be a good compromise between update speed and being able to read a stable plot.
On your phone, start playback of the pink noise file. Start the RTA (red button at top right) and adjust the phone volume so that the REW SPL meter reads in the 80 to 84 dB range. Set the frequency scale for 20 Hz to 20 kHz and the vertical scale for 40 to 80 dB. It should look something like this:
OK! So that's the response of the headphone relative to "subjectively neutral". (In other words, a "subjectively neutral" headphone will have an approximately flat RTA. See the app note Headphone EQ with EARS and REW for more explanation.)
Now adjust the EQ curve in CapTune to flatten out the response. Don't try and flatten it completely, just get the response flatter than it was. This headphone has a the number of strong peaks and dips in the treble, so we have set the EQ so that the peaks line up with the imaginary reference line. Here is the RTA after our EQ adjustments:
Now listen to the headphones and adjust the EQ further if desired. Finally, in CapTune, save your EQ as a profile:
Method 2: Offline sweep measurement
A measurement sweep is more accurate and has better noise immunity than a pink noise RTA. To do this, use REW's Offline Measurement feature. This method is a little more involved than Method 1, so we recommend using Method 1 first.
(As of February 2018, offline measurement is only available in the latest beta version of REW, which can be downloaded from AVNirvana.com.)
Generate a measurement sweep file using REW's Signal Generator. Use the exact same settings as shown in the screenshot below. Click on the WAV button, and then OK in the second box that pops up, to save the WAV file. REW will choose a default file name like "256kMeasSweep_48k_20_to_20000_LR_refL.wav". Then load this file into your phone or DAP.
In REW, check that you have the HEQ calibration file loaded:
With the headphones positioned on the EARS, set the phone volume low and then play the file. Increase the volume until playing the file results in the REW SPL meter reading in the 80 to 84 dB range. Then stop playback.
You will need to record the signal from the EARS. If you don't already have a favorite audio recording program, try Audacity, which is free and runs on Windows, Mac and Linux.
In your recording program, select the EARS as the input source, and set the program to record at 48 kHz. You should record both channels i.e. stereo. Start recording and play the impulse response file once. Then stop recording and save the recording to a WAV file. (If the phone or DAP repeats or proceeds to another track, you may need to edit the recording to remove the extra audio.)
From the REW File menu, select Import -> Import Sweep Recordings. Check the box "Apply cal files."
Now for the fun part: you need to select both the sweep file ("Stimulus") and the recording that you just made ("Response"). Click on the Browse buttons to find these files, and select the same channel that your loaded calibration file is for (i.e. if you loaded the left channel calibration file, import the left channel). The result should look like this:
And that's it! Your measurement will already be in the main REW window. (If you forgot to check "Apply cal files," you can click on the "Change Cal..." button to select the HEQ calibration file now.) Apply 1/12th octave smoothing to the measurement using the Graph menu.
You can now apply your EQ, and then remeasure to see the result. The graphs below show our "before" measurement in red and our "after" measurement in green. For comparison, the pink noise RTA plots from Method 1 are shown in mauve and blue. (We have offset the traces to make them easier to compare.)
Wrapping up[Top]
That's it for this app note! As always, you should listen to a selection of your favorite music and fine-tune your EQ settings. Have fun, and please let us know of your headphone EQ results in our forum.
