What is the Fletcher Munson curve?
3 min readThe Fletcher Munson curve is perhaps the most important graph that all producers need to be aware of. Even if you aren’t a fan of the geekier side of music production, this graph is essential to understand, especially if you want to mix music well.
Above we have a graphical representation of it (blue) with the much more recent revisions (red). The revisions are based on the findings by Fletcher and Munson and are known as the “Equal Loudness Contour.”
Equal Loudness is a much more descriptive name and what these curves show is how the human ear perceives frequencies. Our ears aren’t perfect, and their shapes determine how we pick up sound. Much like how holding a tube to your mouth makes some frequencies more prominent and “honky” the tube in our ears favours certain frequencies.
These curves show the relative volumes for each frequency that we perceive as having an equal volume. You will notice there is a dip in each line between 1000Hz and 10kHz. That is the frequency that we are most sensitive to.
So even though it may be playing at a slightly lower volume than a tone at 500Hz, we hear it as the same volume.
You will notice that the graph also has many curves on it. This is because our sensitivity depends on the volume. At louder volumes, bass is more pronounced (seen by the flatter line).
To explain it better, let’s look at the bottom red line. This represents music played at the quietest volume. The lower the curve is at a frequency, the more sensitive we are to it.
So at that 1000Hz to 10kHz dip, it can be very quiet indeed to be audible, but low frequencies are very hard to detect. This means that to hear the bass, we have to boost the bass frequencies.
Compare this to the top red line, which represents loud music. The bass frequencies are a much gentler slope in comparison to the mid range, which means that the bass doesn’t have to be as loud relatively to the rest of the frequencies.
So what does this mean for mixing?
Essentially, if you mix too quietly, you will need to boost the bass a lot to hear an even balance. Likewise, you might turn down the upper mids and highs because they sound louder in comparison. If you were to then play this track in a club, it would be too bass-heavy. I have this problem a lot when mixing as I have neighbours who I don’t want to annoy. My mixes always come out too bass-heavy on louder systems.
Likewise, if you mix really loudly, your song might not sound as good in quieter environments. You might think there is more bass than there is and so turn it down. If it was played back in quieter environments, the listener may hear it as being quite a thin mix.
So the solution? While many people smarter than me argue that there is a perfect volume to mix at, the rule of thumb is to mix at the volumes you want the listener to hear it at. If your song is destined for the ear-pummelling systems of a techno club, mix loudly (give your ears and neighbours a break regularly). If it is designed to be played on home systems and radios, perhaps mix it a bit quieter.
If you do want to be smarter about it, Sound on Sound do a great guide to setting up your studio levels to a constant (one such industry standard is known as ITU-R BS.1770 which is used in TV and film production).
Thank you for this! Found you through your reddit infographics. Never heard of this, it’s very helpful! I’ve always wanted to mix music well, looking to MGMT for inspiration on making massively layered, complex, intricate, and mind-bending songs, which of course need to be mixed very well. I will continue to follow this website!