JEL,

I hope you don't mind me hijacking the thread for this post but I thought that I'd better explain what I mean in relation to the Fletcher-Munson curves for anyone who hasn't come across them before.


Fletcher-Munson Curves
The graphs below show a collection of Fletcher-Munson curves. In the study of psychoacoustics, these are also known as Equal Loudness Curves.



The above show how the average human hears the loudness of music when different pitches are compared. I've chosen the 80 phon line (circled in blue) as this would be a fairly standard level of loudness.

  • For comparison: normal conversation is around 60 dB; city traffic noise is around 80 dB.

I've also marked two 2-octave jumps (in green). These two sections can be regarded as almost linear. These are 50 - 200 Hz and 200 - 800 Hz. (The x-axis scale is logarithmic and unless one has had practice reading log scales, it's not always clear to see where the values lie. That's why I added the green lines.)

Quote:
As the frequency graph below shows, most music would fit into the frequency range of 50 Hz to 1050 Hz. This is G1 to C6 where middle C is C4

Frequencies


What the 80 phon curve above shows is how many decibels different sound frequencies need to be set at so that they are heard as equally loud. The reference frequency is 1000 Hz set to 80 dB - hence the name 80 phon.


How to interpret Fletcher-Munson Curves
For a frequency of 200 Hz, the 80 phon curve gives a y-value of approximately 85 dB. This is saying that, for the average person, a 200 Hz sound at 85 dB will sound equally loud to a 1000 Hz sound at 80 dB

If a bass note of 50 Hz is played, it will need to have a loudness of around 102 dB to sound as loud as a 1000 Hz sound at 80 dB.

By comparing the 200 Hz and the 50 Hz values, it's possible to see that a 50 Hz sound needs to be 17 dB (102 - 85 = 17) louder than a 200 Hz sound at 85 dB if it is going to sound equally loud. Since 50 to 200 Hz corresponds to a jump of two octaves, 50 to 100 Hz is one octave and 100 to 200 Hz is the second octave, then the decibel adjustment per octave could be approximated by 17/2 = 8.5 dB.

Applying this information...

Let's say that my sounds are all electronically set to 85 dB. The above information tells me that if I want my bass to sound equally loud to my mid-frequency harmony (around middle C), I'll need to increase the low frequency volumes by around 8.5 dB per octave (from 200 to 100 Hz and then from 100 to 50 Hz).

Using a similar argument, if I have a 200 Hz note at 85 dB (instrumental or sung), then to get a note at 800 Hz to sound equally loud, it would need to be at around 79 dB. This corresponds to a reduction of 6 dB over the two octaves. This means that I would need to lower my upper frequencies by around 3 dB per octave. (I suspect that these explanations are part of the reason why Ozone versions 5 and 6 have roll-off guides for 6 dB and 3 dB.)

Using a parametric equaliser, the above information now allows me to begin devising a strategy for shaping my overall sound so that every frequency can sit comfortably in the mix.

Quote:
For more detailed information, have a look at the below article. I'm only a novice and the article is written by someone with expertise.

https://www.soundonsound.com/sos/mar12/articles/loudness.htm

The image of the Fletcher-Munson curves came from the site found at the above URL. The article is well worth the read.

Regards,
Noel

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