alt Hacker NewsI've always found these "perceptual vs absolute" things about human senses very interesting.
Hearing has a few quirks too:
- When we measure sound pressure, we measure it in log (so, every 3dB is a doubling in sound pressure), but our hearing perceives this as a linear scale. If you make a linear volume slide, the upper part will seem as if it barely does anything.
- The lower the volume, the less perceivable upper and lower ranges are compared to the midrange. This is what "loudness" intends to fix, although poor implementations have made many people assume it is a V-curve button. A proper loudness implementation will lessen its impact as volume increases, completely petering off somewhere around 33% of maximum volume.
- For the most "natural" perceived sound, you don't try to get as flat a frequency response as possible but instead aim for a Harman curve.
- Bass frequencies (<110Hz, depending on who you ask) are omnidirectional, which means we cannot accurately perceive which direction the sound is coming from. Subwoofers exploit this fact, making it seem as if deep rich bass is coming from your puny soundbar and not the sub hidden behind the couch :).
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I have a theory that this generalizes to some extent.
Pitch perception is also logarithmic; an octave in music is a 2x ratio.
Memory is sort of logarithmic; you'd say a thing happened 1-2 days ago or 1-2 years ago, but not 340-341 days ago.
Same with age; someone being 10 years older than you is a much bigger deal when you're 10 than when you're 80.
I've played around with this a little bit while trying to engineer the "perceptually loudest ringtone sound". I thought a square wave or pulsed white noise would work well, but I found that the bell-like "telephone ring" seemed perceptually louder.
I now have to read up on the Harman curve because I'm curious about this and it has a direct practical application.
When we measure sound pressure, we measure it in log (so, every 3dB is a doubling in sound pressure), but our hearing perceives this as a linear scale
The way I learned this, at least, 6 dB is what corresponds to a doubling of amplitude, but human ears compress this so it's 10 dB that corresponds to a doubling of volume - this is how the "bel" was supposedly calibrated to begin with. But that wouldn't mean we hear volumes on a linear scale in terms of bels, but rather still logarithmically (perceived volume would just be compressed using the function x^(3/5), which looks closer to sqrt(x) rather than log(x)).
I stumbled upon this when visualizing music. It is very interesting how everything is kind of non linear, like you mention. I had to increase low frequencies and then I got stuck trying to bucket frequencies. It seems humans have different fidelity for different ranges of frequencies
I can't remember the last time I saw a "loudness" button. My receiver from 1980 had one but my receiver from 2000 does not.
A 3dB increase is a doubling of a power quantity, but you need 6dB to double a root-power quantity (formerly called a field quantity). Sound pressure is root-power quantity:
https://en.wikipedia.org/wiki/Power,_root-power,_and_field_q...
Consider a loudspeaker playing a constant-frequency sine wave. Sound pressure is proportional to the excursion of the cone. To increase sound pressure, the excursion has to increase, and because frequency is fixed the cone will have to move faster. If it's covering twice the distance in the same time interval it has to move twice as fast. Kinetic energy is proportional to the square of velocity, so doubling the sound pressure requires four times the power, and doubling the power only gets you sqrt(2) times the sound pressure.
Human loudness perception generally requires greater than 6dB increase to sound twice as loud. This depends on both frequency and absolute level as you mentioned, with about 10dB increase needed to double perceived loudness at 1kHz and moderate level.