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6: lossy compression

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Considering the effects of simultaneous masking, spectral slits and other psychoacoustic principles, it becomes apparent that a sound stream can eliminate certain components, (typically for the sake of reduced storage space requirements) and remain un-compromised (as far as is perceivable by a human ear).
Additionally, many of the illusion files in this forum demonstrate how unreliable human hearing actully is; its selectivity can be swamped drastically, it presents a different spectral balance when exposed to deviations as small as 1/4 db, its memory is very poor and it 'makes things up' all the time
Research into practical applications for psychoacoustic principles has lead to the development of several lossy compression algorithms; when applied appropriately, these algorithms arrive at a much reduced data stream from the original sound sample, yet listeners (due to their being human) often can't discern between an original sound and its lossy counterpart.
The trouble comes when un-informed individuals unilaterally decree that MP3 files sound horrible.  Factual data from actual research shows that 90-95% of human ears can't distinguish between original and compressed.
Deniers often point to ill conceived, low-bit rate samples (which display horrible compression artifacts) as proof that MP3 is low fidelity; this is no surprise, as trying to stuff 600 songs onto a disc at 64kbps WILL result in a sound laden with artifacts of compression
Carver site! has provided, for those interested in empirical evidence, a sequence of files that demonstrate how effective modern MP3 CODECS can be
In the years since these files have been available, only eight have reported their experience in comparing (and there IS a relatively easy to distinguish, 128kbps file in the mix), and of those reporting in, only one person has been extremely close (and he admitted he was guessing)
From the relatively slim reporting rate, I received all manner of comments; some preferred the VBR file (Many did in fact) and mentioned that it had better imaging than the original, or a quieter noise floor
Some were CERTAIN that the original file was flat, 'hollow' and 2 dimensional when compared to the VBR
In BOTH of these instances, the listeners THOUGHT that VBR was the original file
This was particularly the case with some members who profess to have 'golden' ears, and persist in deriding the format
YMMV, and be careful out there; willful ignorance is contagious 
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....YMMV, and willful ignorance is contagious....
I enjoy your technical posts Rich, but comments like that turn me off and are sure to rile the members.
You have two choices in life when it comes to truthful observations by others that anger you: You can be ashamed and cover it up by letting your pride take you in the extreme opposite direction, in order to make the point that they are wrong. Or, you can break down the walls of pride by accepting vulnerability as a strength, not a weakness. As you walk through your vulnerability, you will meet humility on the way to courage. From here, courage allows us to let go of shame and rise higher into the person we are meant to be, not the person that needs to be right. This is the road to confidence and self worth.Shannon L. Alder 
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