
The Ghost in the MP3 - whalesalad
http://ryanmaguiremusic.com/theghostinthemp3.html
======
daturkel
For what it's worth, the presence of seemingly significant signal in the
difference between the original and compressed tracks does not _necessarily_
mean that significant sonic/perceptual loss has occurred. Operating correctly,
the encoder is designed to cut not just sounds that the human ear cannot hear
in general (e.g. sounds above 22kHZ) but also sounds which may not be
perceptible _in context_ (e.g. the quietest signals in a loud section). So if
you find something beautiful about the ghost tracks (and I think there is
something beautiful to find), don't immediately jump to concluding that mp3 is
awful for cutting these sounds—they might be hardly perceptible when added to
the mix.

Of course, at high-compression rates mp3 does begin to significantly degrade
fidelity.

Edit: all of this is not to put down the project—I still think it's pretty
cool as art and as a demonstration of the encoder, I just didn't want people
to think that this was some sort of massive failing of mp3.

~~~
derf_
> Operating correctly, the encoder is designed to cut not just sounds that the
> human ear cannot hear in general (e.g. sounds above 22kHZ) but also sounds
> which may not be perceptible _in context_

This.

The idea is called "masking", and a well-designed encoder explicitly removes
the most details from areas where they are masked by other, louder parts of
the signal. See the presentation on CELT I gave at linux.conf.au in 2009, and
in particular listen to the audio samples that go with slide 47:
[http://www.celt-codec.org/presentations/](http://www.celt-
codec.org/presentations/)

~~~
logfromblammo
Look into the sky at night during a new moon, and count the stars. Look again
during the day. The stars are still there, but the atmospheric diffusion of
blue light from the sun prevents you from discerning the fainter light of a
more distant star.

Lower yourself to the bottom of a deep well during the day, and look up again.
You can see the stars again, because the diffuse blue sunlight is much weaker
there.

If you were to compress an image of the daytime sky in the same manner that an
MP3 compresses audio, you could simply remove all that variation from faint
stars and only keep the information from bright sunlight. Follow the ghost
discovery technique by taking the difference between the original and the
compressed image, and you will see an image resembling the night sky. But most
people would not be able to discern much of a difference with the naked eye.

For audio, if you have a pianissimo piccolo solo, and someone plays a crash
cymbal in the middle, you could remove some of the harmonics from the melody
because humans are incapable of hearing them, and you can also remove that
portion drowned out by the crash, because humans can't hear quiet sounds
through louder noises.

Finding the "ghost" track is actually revealing all the sound in a piece of
music that no one ever hears anyway, whether the track is compressed or not,
simply due to the hardware limitations of the human auditory system.

------
microcolonel
“Listening tests, primarily designed by and for western-european white men,
and using the music they liked, were used to refine the encoder.”

Not to be oversensitive, but would it be okay to say something like this if
Fraunhofer IIS were in... Japan or something, and they happened to find a lot
of Japanese people who liked Japanese music for listening tests?

“Listening tests, primarily designed by and for east-asian yellow men, and
using the music they liked, were used to refine the encoder.” Would probably
come off a bit rougher, ね？

FWIW the tracks were interesting to listen to, and I've had fun doing this as
well. I recommend trying it with the Opus codec. As for the sensibilities of
the author, I hope they can get over their paranoia about audio codecs being
an ethnocentric conspiracy to destroy "the sounds they didn't want us to
hear".

~~~
colanderman
In the United States, "yellow man" is considered pejorative, "white man" is
not. In isolation this seems illogical as they are structurally analogous, but
words do not have meaning in isolation. The meaning of a word entails its
historical use by a society.

~~~
Groxx
I dunno. I _almost_ exclusively hear "white man" used as an insult. Not long-
term historically certainly, but certainly now - it's almost always
accompanied by the implication that white men are racist (and/or sexist).

------
pistle
I would appreciate a couple examples showing more typical bitrates at 256kbps
and 320kbps. I like what it is, but there's this lossy difference between the
argument being made and reality. Now, if I could get a copy of the intended
argument, I could invert the phase with this site and show you the difference.

~~~
orbitur
The argument being made is more about art, not "mp3 bad".

~~~
Dylan16807
Okay, but the art is dancing around an actual important technical question
without answering it, even though it would take far less effort to do so.

~~~
bodyfour
I'd refer you to the top-voted comment from @ daturkel. Because of the
psychoacoustic models used for lossy audio compression (and, in particular,
the "masking" effect) listening to these delta signals won't give you useful
information about the compressor's accuracy.

~~~
Dylan16807
I disagree. It gives you information you have to treat carefully, but it is
useful.

Especially to compare different bitrates. I'm not even sure what bitrate this
used, maybe 128 like the example files?

------
userbinator
Reminds me of this article a few years ago, where college students actually
preferred music with MP3 compression artifacts in it:
[http://radar.oreilly.com/2009/03/the-sizzling-sound-of-
music...](http://radar.oreilly.com/2009/03/the-sizzling-sound-of-music.html)

~~~
bni
Has this been reproduce somewhere else? I have always been very sceptical of
that claim since I first read it.

------
odonnellryan
What I find amazing is that someone decided to create this, just because they
could.

I find that a lot more interesting than anything learned, strangely.

~~~
dublinben
This is hardly innovative or creative. People on audio forums have been
playing around with this technique for years. It is literally a mechanical
process.

~~~
chillingeffect
Exactly. OP doesn't have enough to complain about, so he's literally
hyperfocusing on nearly imperceptible artifacts and amplifying them...

...in order to weakly raise a vague grumbling about "European" audio
engineers.

Even though he has no evidence to support that claim.

Yes, Fraunhofer is a German company, with headquarters in Munich. But did OP
know they employ 23,000 people, with centers in the U.S. as well as Asia?

He could have looked that up, but it's so much easier to just throw bullshit
out there and hope it resonates with people ashamed of their ancestors.

MP3 is not one single technology that all came from Fraunhofer. It is an
accumulation of several areas of technology, including types of filters,
compression as well as the perceptual stuff. I once traced it through the
research literature all the way back to voice compression protocols for the
American F15 (16?) in the 1970s!

And if you're reading this far, you're probably totally obsessed like me and
you might want to check out my associate Jonathan Sterne's book on the history
of MP3 from a cultural perspective [0].

[0] [https://www.dukeupress.edu/MP3/](https://www.dukeupress.edu/MP3/)

Sterne traces the history of perceptual encoding all the back to the early
1910s! It's not just some pop-tech designed in 9 months for a quick buck!

Finally, audio engineers is a term that generally means people who work with
sound in a studio or recording context, who produce audio for projects with
specs. MP3 was designed by _scientists_ who produce work _about_ audio, not
audio engineers.

------
kleer001
White text on black background? Center justified text? I love the sound, but
the page is making my eyes bleed.

------
krick
Nice and interesting, but doesn't soundcloud use some compression itself? I
mean, isn't it different from simply posting some FLAC file? I don't know,
just wondering.

~~~
e12e
"Does SoundCloud convert my files to mono? We don't modify original audio
files that are available for download. For streams, we convert the original
into MP3 Joint Stereo for streaming."

------
MrJagil
Sounds somewhat familiar to what you can achieve with Paul Stretch. I assume
it has something do with phasing...

------
sdeyerle
I would be very interested in seeing a comparison of codecs and bitrates done
in this way.

------
mahouse
Tip: disable Ghostery or you will not understand what's going on...

