The Fletcher-Munson curve of 60 phon is defined as 60db sound pressure level (at your ears) at 1Khz. 60db is considered the level of normal conversation. If calibrating to 60db SPL then you use the 60 phon curve for the subsequent test. The starting loudness of the other frequencies will be adjusted using the curves.

I chose 1047Hz (note C6) as the reference frequency, as it is close to the 1Khz frequency from which the Fletcher-Munson equal loudness curves were derived.

I've read somewhere that headphones are better than speakers for discriminating loudness differences at lower frequencies, and poorer at high frequencies.

Perceived loudness difference is greater at soft listening levels than at loud levels.

An explanation of equal loudness can be found at:

Create a new project. Name it "Hearing Test", or whatever you wish.

Insert a new track.

Insert a JS tone generator on that track.

Disable the tone generator so it isn't outputting a tone.

Leave tone generator wet mix gain at default -12db.

Set track gain to -18db.

IMPORTANT! The tone generator gain settings and the track gain must not be changed throughout testing, or it will invalidate the test results. Tests may be set up with the wet mix gain and/or the track gain at a different level than the default. Do this by making the adjustments in the "Calibration" section, accessed by clicking the "Edit" button. That way the settings will be saved in the "profile". I originally added this section for experimentation, but decided to keep it in the event anyone finds it necessary.

The DAW settings level should now be -42db below max. peak. This should leave plenty of headroom for running the tests. These settings represent the level sent to your output device: audio interface, speakers, headphones, etc.; not the sound pressure at your ears.

The sound pressure level in decibels that you hear is determined not only by the above DAW settings, but by any hardware settings between your DAW, up to and including your headphones/speakers. You will need to set your headphones / speakers to 60db sound pressure level at listening position. Do this by adjusting an audio interface or your speaker output directly. If those options are not available you will need to adjust the tone generator gain to achieve the desired levels, as noted above. At higher sound pressure levels it takes less gain to perceive equal loudness. My preliminary testing bears this out.

Set the tone generator to use note "C" and octave +1. This is our reference frequency of 1047Hz. If desiring to change the tone generator wet mix gain do so in the "Profiles" editon by clicking the "Edit" button. Enable the tone generator, then set the gain.

Play the tone.

Calibrate using an SPL (sound pressure loudness) meter: Adjust the speaker/headphone volume (or the tone generator gain) until 60db sound pressure level is achieved at your ears. If you don't have an SPL meter there are some phone apps available. I cannot attest to their efficacy.

Subjective calibration: The Fletcher-Munson curves all have basically the same shape, except for their scale. So, if you're not exactly at the correct phon level, the perceived gain differences will be in the correct direction, and should be in an acceptable range.

Assuming normal conversation is 60db, and assuming that your mid-range hearing is okay (here comes the very subjective part):

Adjust the speaker volume until you think it is at that of normal conversation.

Once you have your test calibrated this becomes the level for which the entire test is based. This level must not be changed or it invalidates all other test measurements.

Note the settings. I run my output through an audio interface, then through a Big Knob to the speakers. If I want to repeat or continue the test later, it will need those settings. Perhaps save as a profile: [ speaker level / headphones level; etc. ]

Proceed to the test now that 'calibration' is done.

Select the track that has the tone generator from the Track select box.

Select a frequency (other than the 1047Hz reference) to test.

In the Channel radio box select which channel is to be used for the test: left, center, or right.

Make sure the Locked checkbox is not checked. If checked that frequency is considered locked and a test cannot be performed on it.

The Bypass checkbox does not affect any testing. If it is checked then any resulting test data, although it will be saved, will not be included in the resulting dataset.

Press the Start button to start the test. The tone generator will produce bursts of tones alternating between the selected frequency and the test frequency. Use the "Inc Vol" or "Dec Vol" buttons to adjust the test frequency's loudness until it appears equal to the reference tone.

When satified press the Stop button to end that frequency test. The test results will be saved internally.

Repeat for each desired frequency and/or channel.

I discovered that I also have hearing differences between my left ear and my right ear; not just with perceived volume, but with perceived pitch. Although this is mostly prevalent at very low frequencies, I still found it unsettling. Nevertheless, I developed a simple test to measure the differences.

Prepare the app as for the Main Test. The channel setting doesn't matter. Press the Start button to start the test. The tone generator will produce bursts of the test frequency tone alternating between the left channel at the predetermined volume and the right channel. Use the "Gain" knob to adjust the volume of the right channel until it appears the same as the left. Use the "Cents" knob to adjust the pitch of the right channel until it appears the same as the left. The gain adjustment is limited to +-9db, and the cents adjustment is limited to +-100 cents (a full semitone).

Press the Stop button to end the test. The test results will be saved internally.

A set up can be saved as a profile. This is useful if you use different configurations for your tests. You may have one profile for using a particular set of headphones, and another for using a pair of monitors. Click the "Edit" button below the "Profiles" select box to open the profiles editor. There you can add, rename, or delete profiles. Profiles are saved in reaper-extstate.ini file. Select a saved profile from the "Profiles" select box to load it.

Click the "Print" button to write the data of the currently selected profile to the console window. You can use this data to set up an equalizer to compensate for any hearing deficiencies you may have. If the data shows that you have a hearing deficiency (as compared to "normal" hearing) then you can insert a band at that frequency, boosting its gain to compensate. You would probably want to adjust it's Q for a smooth transition.

Use the equalizer as the last fx on your master track. Enable the equalizer to hear your music closer to how someone with normal hearing hears your music. Disable the equalizer to remove your adjusted bias from the mix. Personally, I will probable use an equalizer for each channel as I have significant differences in my hearing perception between my left and right ear.

The graph plots a point for each frequency of the currently selected channel of the currently selected profile. The graph has two modes: "C" and "F". "C" displays the Fletcher-Munson curve overlaid with the profile's data points and their deviation from it. "F" is a flat graph displaying each frequency's gain deviation from "normal".

Click the "Prefs" button to open the Preferences window. Here you can change the script window scale and / or theme.