The LF Problem: Low Frequency Expansion in Our Hearing

One of the key problems revealed here is the low frequency expansion that exists in our hearing. This is a very serious, essentially unsolvable, problem that explains why we have such trouble with low frequency decisions in mixing and mastering. Take a look at Figure 9.

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Figure 9 shows the actual amplitude change that occurs, on average, for us to perceive a 10 dB change. The big problem is that this amplitude varies as a function of frequency. Further, the difference between percveived loudness and real amplitude change is quite signficant. So, small changes in actual amplitude result in comparatively large perceived changes in low frequency.

By the same token, low frequency anomalies, peaks, dips and the like caused by the speaker design and its placement in the room are multiplied. Think of our hearing as a low frequency expander. See Figure 10.

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	Shows the expansion ratios for the bottom eight 1/3 octave bands. 1.6:1 is a heap ‘o expansion! No wonder we can’t get the bottom end right!

It gets worse when we think about the range of end-user systems. It’s bad enough that we mix on a quirky, ported monitor in a pretty odd-sounding room, but then our mix is supposed to “travel” to thousands of different quirky speakers in zillions of different rooms, all while our hearing multiplies the errors!

Some limitations to keep in mind

Before you let this news completely ruin your day, there are a couple of things to keep in mind. First, the Equal Loudness research was done with sine waves, and it may be that the actual complex perceived spectrum at these various levels isn’t quite as perversely different as these graphs suggest.

Second, we’ve been living with these curves in our collective heads for a long time now, and we’ve managed to survive. Our perception of these response changes is tempered by the accompanying level change and the masking effect of consciousness, so it isn’t quite as frustrating as the graphs look.

Nonetheless, there are some things to think about here, obviously.