How to record your own simple headphone correction profile IRS!
(this ReaPlugs ReaFIR plugin makes drawing EQ curves a breeze! It's a linear phase EQ though, when ideally for headphone correction we want a minimum phase EQ. I use a different VST EQ module called Electri-Q, it's not so easy to plot the curve the way you want on it but I hope the difference in quality is worth it
There are some caveats to this curve drawing that you may run into but I don't know how to summarize this--if you run into trouble I'm more than willing to help
Just hope to see you share your completed IRS here in this thread, they will be added to the collection with your permission and credited to you in the filename
1. Download Audacity and _32 bit_ version of Reaper ReaPlugs
2. Install Audacity with default settings. Install ReaPlugs in Program Files (x86)\Audacity\Plug-ins (I tested this by deleting the \VstPlugins subfolder the installer automatically appended to the directory name while installing, I don't know if this is necessary)
3. Open Audacity and it should automatically scan and find the ReaPlugs vst plugins. If this is not your first time running Audacity go to Edit->Preferences->Effects->check Rescan VST effects and close and restart Audacity to load the ReaPlugs.
4. Generate a track of 30s of silence. Generate->Silence
5. Press Ctrl+mouse scroll upward on the sound track to zoom all the way in to individual sound samples
6. Use the pencil tool to draw on the sound track and bring one single sample of sound to the ceiling. This creates a perfect impulse.
Then click on a blank area of the track header on the left. This selects the whole audio track for effects processing.
7. Open ReaFir by choosing Effect->Cockos: ReaFir (ReaPlugs Edition)
8. Change the top and bottom dB limit of the vertical scale to a smaller range so that you can plot more precisely. For example, with a -10 to 10 range the app conveniently puts scale lines at 5dB intervals, matching the 5dB scale on some headphone measurement sites. (although many graphs require a larger range than -10 to 10)
9. Plot an upside down version of the headphone frequency response graph you found for your model of headphone
Take care to plot the points at the correct x and y positions
For example, note that most measurement graphs only go down to 20Hz but the graph on ReaFir goes down to 0
Also the scale from 10-20kHz is wider on ReaFir. When you press and move a point around you'll see a box showing the current frequency and dB amplitude so look at that to make sure you're putting the point at the right place
IMPORTANT NOTE: most headphones will have a big dip in the graph somewhere or fall off a cliff at the bass or treble end of the scale. You should not draw the curve exactly as the inverse upward cliff at these points--because the taller your graph in the vertical scale (the larger the scale of frequency response correction applied), the more negative gain needs to be applied at the next step to prevent clipping. I have received consecutive reports of people following this tutorial to the letter and producing graphs that span 30+dB of vertical scale. The resulting IRS are so quiet as to be unusable. Please keep this in mind when following this step. Note the maximum volume you have had to push your device to drive your headphones when no effects are applied and think about how many dB of volume you can afford to lose when applying the IRS, and take the downward plunges of the graph with a grain of salt when plotting the corresponding upward compensations. A rule of thumb is your graph should never go up more than 10dB above the zero line.
10. Take note of the dB value of the highest point of the graph and set the output gain to the negative value of it
As noted above this will make music convolved by this IRS quieter by as many dB. If you find yourself applying an unreasonable value here review what you've done in step 9 and revise the curve as necessary.
11. Save your work with the Save button on top, then press OK to run the filter on the sound track!
12. The impulse would have moved some way down the track after the processing. Zoom out by pressing Ctrl+mouse scroll down on the track to find the location of the impulse.
13. Select 16384 samples of the track with the impulse centred on it by clicking somewhere to the left of the impulse and then setting the selection length to 16384 samples. Might take you a few tries to find the right position
(click on the drop-down menu to select "samples" first)
14. Select Edit->Copy to copy down the 16384 samples then delete the whole audio track
Then select Edit->Paste to end up with just the 16384 samples of audio with the impulse centred on it.
Then select Edit->Duplicate then go to the context menu for the first audio track and select "Make Stereo track" to end up with left and right channels playing the same impulse.
15. Select File->Export; under "save as type" choose "Other uncompressed files" and click options...
Choose header to be wav (microsoft) and encoding to be... well I've been using signed 32 bit pcm so far but you may try 32 bit float as well and see if that works
16. Hit save, rename the wav file produced with .irs suffix, put it on your android and enjoy!