
The Missing Fundamental - hatsunearu
https://hatsunearu.github.io/dsp/audio/electronics/software/2018/04/08/missingfundamental.html
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hatsunearu
Hey, this is my first blog post--I got motivated to write one because of all
the cool stuff I find on HN.

I wanted to write a single blog post on bass boost (as mentioned at the end),
but I wanted some early feedback on my writing so I split the original blog
idea into two.

Obvious points for improvement are the code (playing more than N seconds, etc)
and writing some CSS for it, but I'm looking for some readability issues in
writing if there are any.

Thanks for reading!

~~~
fhood
Well, it was an awesome blog post. I have actually lost sleep pondering how
itty bitty iems manage to have bass response. Thanks.

~~~
aidenn0
IEMs can have pretty good bass response just because they don't need to
generate much volume. Hold them about an inch from your ear and turn the
volume up high enough to hear from that distance. Very little base at that
point.

~~~
aoeusnth1
It's not just the low volume - it's the airtight seal. A very low frequency
sound wave is a slow sequence of low- and high-pressures. With an airtight
seal, it's much easier to sustain pressure differences from 1 atmosphere from
a long time. With no seal, the high or low pressure leaks away from the region
near the ear.

This is also why open-ear headphones tend to have lower bass response than
closed-ear headphones. For example, compare these frequency response curves:

[http://graphs.headphone.com/index.php?graphID%5B0%5D=853&gra...](http://graphs.headphone.com/index.php?graphID%5B0%5D=853&graphID%5B1%5D=4323&graphID%5B2%5D=&graphID%5B3%5D=&scale=30&graphType=0&buttonSelection=Update+Graph)

The open-ear Sennheiser HD650 has around 10-12 db lower bass response than the
closed-ear Fostex.

Even more dramatic, look at the dynamic response to a 50hz square wave - the
Sennheiser's amplitude drops completely to zero before the next jump of the
square wave, while the Fostex manages to maintain about 1/3 of the original
air pressure in the headphone cup by the end.

[http://graphs.headphone.com/index.php?graphID%5B0%5D=853&gra...](http://graphs.headphone.com/index.php?graphID%5B0%5D=853&graphID%5B1%5D=4323&graphID%5B2%5D=&graphID%5B3%5D=&scale=30&graphType=3&buttonSelection=Update+Graph)

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tylerhou
Maybe my headphones aren't too good (airpods), but when I remove the
fundamental I hear octaves, thirds, and fifths of the fundamental as chords
instead. I also have a bit of musical training as well, so that might be
helping me distinguish.

EDIT: If I turn the last four sliders all the way up (5-1-3-5), I can barely?
hear the tone of the root below the first 5 (the second slider). I can't hear
any tones of the very first slider, possibly because there aren't any tones
between that and the jump to the next octave.

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duncancarroll
Maybe I don't understand exactly what I'm supposed to be listening for, or
maybe my ears are bad, but I don't think I can hear the missing fundamental
unless it's actually being played.

I also don't quite follow how arbitrary harmonics can result in a specific
note--is the idea that if you conjoin any 2 or more harmonics of Note X, their
pitch will sound like the pitch of Note X even though it is not technically
being played?

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KozmoNau7
I have a device that does this (among other things). It's a discontinued
product called the Boomcloud Boomstick. It really does make mediocre
headphones sound like they produce deep bass.

There have been other similar devices, particularly the SRS Wow! Thing is
still popular among musicians, and commands high prices on eBay.

I bought the Boomstick for a DIY BT speaker project, that I had to put on
hold. I may pull myself together and actually finish it now :-)

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tomphoolery
> It is as if the brain knows that the harmonics are related to the
> fundamental in integer multiples, and calculates the fundamental all
> subconsciously.

Isn't this fundamentally (no pun intended) how overtones work?

~~~
hatsunearu
Overtones are another name for harmonics. The only thing that's different is
the naming scheme: the first overtone is the second harmonic, and the Nth
overtone is the N+1th harmonic.

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dvdplm
I like the writing a lot, perfect balance for people without musical training
(and an interest for sound). Well done!

Side note: the JS to play sounds throws an error in Safari TP, works fine in
FF.

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weber111
This is really cool!

I was able to hear the fundamental with its slider turned all the way down and
the harmonics up using decent in-ear headphones

