The Ghost in the MP3
ryanmaguiremusic.com
ryanmaguiremusic.com
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.
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/
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.
IIRC LAME which was used for this project, replaced the entire psychoacoustic modelling code (which is possible to do since MP3-the-format only cares about frequency bands and buckets, not about what the encoder does to them), and they likely tuned their new model to larger, more diverse sets of samples and ears.
There is good reason to think that's different. Audio quality that's measured by subjects' ability to perceive, and report perception of a sound masks the difference between their ear being unable to detect a signal, and hence no signal comes over the auditory nerve and a situation where a soft sound might not be noticed in a loud passage but the ear responds to the signal.
Is this significant? One would probably have to do an FMRI study to answer that. In some applications, like understanding the words of someone speaking, by definition it isn't. But music is emotional and there might be aspects of music listening that are outside the ability to consciously report.
An obvious case of audition working when we can't consciously report what we hear is when we are sleeping, but experiments can detect the influence of those sounds.
Especially to compare different bitrates. I'm not even sure what bitrate this used, maybe 128 like the example files?
I find that a lot more interesting than anything learned, strangely.
...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/
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.
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".