Question: I have friends that are very picky when it comes to MP3 bitrate, and will always look for the 320 kbps version of a file. However, I have never noticed any differences, they sound the same to me. I remember reading somewhere, can't remember where, that the human ear is simply incapable of sensing the difference, even if present.

Can anyone shed some light on the 192 vs. 320 kbps issue?

Answer: 
Here is one surprising result, from an experiment described in Maximum PC's article "[Do Higher MP3 Bit Rates Really Pay Off?](http://www.maximumpc.com/article/do_higher_mp3_bit_rates_pay_off?page=0,0)":

Its conclusion:

> 
> [No other] Maximum PC Challenge has ever surprised us as much as this one. It’s downright humiliating, in fact, that in many cases, we were unable to tell the difference between an uncompressed track and one encoded at 160Kb/s, the bit rate most of us considered the absolute minimum acceptable for even portable players.
> 
> 
> Some follow-up testing confirmed our suspicions: variable bit rate encoding makes a tremendous difference in the audio quality results, certainly enough to justify—many times over—the slight file size increase. Capping the bit rate at 160Kb/s in MP3 files can be pretty harsh on a track, but allowing the bit rate to wander upwards during more complex passages—as variable bit rate encoding does—and throttle down during quieter sections captures an astonishing amount of complexity while keeping file sizes down to an impressive minimum.
> 
> 
> 

I myself took a similar test and failed as much as I succeeded in identifying which track was which (160 vs 320), a result which is no better than random guessing. I can hear a very slight difference most of the time between LAME-encoded (--alt preset standard\*) MP3 files and CD audio, but only on an expensive system with terrific speaks in a quiet room. For earbuds and car listening it doesn't really seem to matter.

The biggest difference seems to be not in 160 vs. 320 but CBR vs. VBR.

\* "Current consensus is that settings "--alt-preset standard" are recommended for most cases. This results in a very high quality VBR MP3s, giving you bitrates around 200kbps, depending heavily on the music. Mellow rap can go much lower and loud heavy metal can result higher bitrates. The quality will always remain very high." — [cd-rw.org](http://forums.afterdawn.com/thread_view.cfm/1912)

**Addendum 7 years later**

Rick Beato has a great video on this topic, which I just discovered on YouTube: [Audiophile or Audio-Fooled](https://www.youtube.com/watch?v=YgEjI5PZa78).
It really depends on a number of factors. Some of them are:

* The age of the listener, the older you get, the less high frequency sounds you can [hear](http://www.roger-russell.com/hearing/hearing.htm). Besides age, there are [more individual factors](http://www.ncbi.nlm.nih.gov/pubmed/3558959).
* The quality of the music equipment, on a nice home stereo you are much more likely to note a difference than on an Ipod on a busy street.
* The quality depends on which encoder program was used. The encoder basically decides which sounds to encode in the audio stream and which sounds to omit. Encoder programs have a [psycho-acoustic model](http://en.wikipedia.org/wiki/Psychoacoustics) that tells them which sounds are important to the listener and which ones not so much. The quality of the output depends a lot on the model (and therefore the software that was used to encode the MP3).
* The kind of music you listen to makes a difference.

Conclusion: it is **not only** about the bit rates.

These and more points are addressed in this introductory article from Karlheinz Brandenburg (Co-developer of MP3): [MP3 and AAC explained](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.26.5956&rep=rep1&type=pdf) (PDF, 143KB).