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Music Listeners Test 128kbps vs. 256kbps AAC
notthatwillsmith writes "Maximum PC did double-blind testing with ten listeners in order to determine whether or not normal people could discern the quality difference between the new 256kbps iTunes Plus files and the old, DRM-laden 128kbps tracks. But wait, there's more! To add an extra twist, they also tested Apple's default iPod earbuds vs. an expensive pair of Shure buds to see how much of an impact earbud quality had on the detection rate."
Not only that, but audio professionals typically do codec and compression tests using an ABX test.
http://en.wikipedia.org/wiki/ABX_test
This would have been more interesting if they had used a statistically valid sample size and not only compared 128 to 256, but also to lossless.
Many similar tests have proven that most humans have trouble detecting any change in audio quality above 160->192 Kbps or in mp3s. A quick web search will show that even "audiophiles" really can't discern the difference. 128 has a clear "tinny" quality that disappears as the bit rate goes up. Based on this, I believe that 256 tracks as compared with the original cds would never be accurately identified. Clearly this should have been a part of this test. The idea that "lossy" means "audible" has not been proven in any real world tests.
The big difference that the 256 Kb/s + DRM-free option makes for me is that now I'll buy albums from iTunes Store. Previously I would use iTunes to buy one to three tracks if there was some artist I liked but didn't want a whole album from. But usually I order the CDs online for $8 to $14, rip them to AAC at 192 Kb/s, and put the disc away to collect dust on my overflowing CD rack. Now I can get higher quality cheaper and faster.
Yes, ideally I would rip all my music to a lossless format. And ideally everything would be available on SACD at 2822 KHz rather than 44.1 KHz CDs. But that's just not practical with my 500+ album collection. It'd fill up my laptop's hard drive real quick and allow me to put only a fraction onto my iPod.
I'm also disappointed that the article only tested the tracks on iPods with earbuds. Most of my listening is on a decent stereo system fed from my laptop. Ripping is about convenience, not portability. I only use my iPod when riding the Metro or an airplane. With all the outside noise the bitrate doesn't matter.
And being DRM-free isn't just a matter of idealism. I get frustrated when I go to burn an MP3 CD for my car and discover that one of the tracks I selected is DRMed. Sure there are ways to get around it, but it's just not worth the bother.
AlpineR
The MPEG community uses a MUSHRA test* to judge the quality of new codecs and to decide on bitrates etc. If there are n-codecs under test than the subject can switch A-B style between n+2 different versions of the same piece of music. These are the n-codecs and a reference or lossless version. He does not know which is which. He can also switch to one which he knows is the reference track (so the reference track is in there twice, labelled in one case and not labelled in the other). The task is to rate (0-100) each of the unknown tracks based on how similar it is to the reference track. One important thing to remember about the task is that the subject must rate similarity, rather than 'quality' or anything else. A certain codec could, for instance, add a load of warm bass to a piece of music making it more pleasurable (maybe) to listen to, but decreasing its similarity to the reference piece. The idea is that the subject should be able to pick the reference track from the unknowns (giving it a score of 100) and then rate all of the other unknowns in terms of similarity to the reference. The codec with the highest score wins. This type of test would be carried out for each of a number of pieces of music, with a lot of listeners.
* sorry, I've no good link- it's in ITU-R BS.1534-1 "Method for the subjective assessment of intermediate quality level of coding systems".
True, the only time you will generally notice the difference is if the track has a crowd clapping or drumkit (hi-hat) cymbals. At 128k I think cymbals sound horrible and undefined. At 192k I start not to be less annoyed.
Can anyone explain this to me? I know what aliasing is; basically it's when your top frequencies hit the Nyquist limit and kind of bounce back downward (how's that for scientific?), and I know what it sounds like. However, the last time I checked, you'd remove aliasing by cutting high frequencies out of the final analog wave with a lowpass filter. Unless something's radically changed since then, wouldn't the presumably lower-response Apple buds actually show less aliasing that the expensive ones that can better reproduce the higher (and unwanted) frequencies?
Or have I been trolled into reasoning with audiophiles? If that's the case, let me know so I can pack up and go home.
Dewey, what part of this looks like authorities should be involved?
Actually, I notice a huge difference between 128K and 192K when listening to classical music. For music that doesn't contain the brashness of percussion or brass instruments, the distortion at lower encoding levels is fairly good; however, brass instruments (including brass cymbals) in particular are unbearably distorted when 128K is used but come across rather cleanly when >192K is used. I've finally accepted that a variable rate between 224K and 320K is where I need to encode my tracks in order to make them as close to the original CDs as I can tolerate without using the actual CDs.
The Overrated mod is for reversing inappropriate, positive mods, not for voicing disagreement with a post.
The Red Book standard unfortunately went with 44.1 (for some esoteric reason having to do with syncing with an analog video standard or something back in the 80s).
;-).
Huh, you're right...
http://www.cs.columbia.edu/~hgs/audio/44.1.html
I always assumed that 44.1kHz was chosen because they took the necessary (Nyquist) sample rate to be able to record up to 20kHz (40kHz), and added a bit for good measure. There's always been that rumor that the time length of a CD was chosen to be able to fit Beethoven's Ninth Symphony, so I always figured they knew they wanted 16 bit, and a length of about 74 minutes, and just picked the >40kHz sampling rate that would get them there with that fancy new "CD" technology that was being developed. I'm happy to know that we're all using 44.1kHz for an even stupider reason
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