Latest AAC Encoder Comparison Results

bullitB writes "For fans of the world wide patent conspiracy's latest audio format, the latest double blind AAC encoder comparison test results are in. If nothing else, this suggests much of the complaints regarding the iTunes Music Store's lossyness might be unfounded."

Discussion

You can discuss this test with the author and others at http://www.hydrogenaudio.org

A warning to potential HA posters

For good reasons, the posters on Hydrogenaudio don't take kindly to people making unfounded assertions about which codecs are better, so if you're going to argue with them, think twice and ABX [hydrogenaudio.org] first. You will be, after all, arguing with many audio developers, e.g. people who make contributions to LAME, people who've tuned the Vorbis encoder, and a surprising number of people who work for Ahead (makers of Nero, of course).

go AAC

Glad to see development on AAC's sound quality...especially on the free side with the vast improvement of the previously terrible quality of FAAC. More 'useful' (although it would stir the pot a bit more) would be a comparison with the latest MP3 encoders. To stay within the AAC bubble in comparisons won't encourage people to convert (or to stay away).

Re:go AAC

here

http://www.rjamorim.com/test/64test/results.html

and here

http://www.hydrogenaudio.org/index.php?showtopic =1 3464&

Re:go AAC

You mean FLAC.

FAAC is another AAC codec.

Re:go AAC

Is anybody else in this subthread plagued by associations with the sound of a duck squawking "AFLAC!"?

Lossy is lossy

When will people realise that half the trouble with a lossy format is transcoding? Sure, AAC may sound high-quality when it's in its original format, but when you transcode it to MP3 for your MP3 player, the quality turns to shit. This is inevitably the case when dealing with lossy formats, and why I'd rather buy CDs and rip them to FLAC [sf.net].

Re:Lossy is lossy

*(Anybody burned them and then ripped them to mp3 from the CD? I can imagine that would be less lossy than straight transcoding.)*

if every device was perfect it would be bitwise identical. and what in the world led you to believe otherwise? if you ran it through analog form in some point you might get 'smoother' sound or something but that's just it and self deceit.

that being said, if you buy music for an mp3 player, buy it in mp3. or rip it yourself from a cd, or just get high enough bitrate it doesn't matter for your golden ears if you code it from one format to another.

better yet buy from some independends that are willing to provide both formats. or fuck, just encode good old amiga mods.

Re:Lossy is lossy

Why would you go from AAC to MP3?

To load it in your mp3 player?

Unfortunately...

Winamp 5.02's encoder (which got a lot of help from hydrogenaudio's own Menno, a FAAD AAC-decoder developer/Ahead MPEG4 developer) wasn't included in the listening test because of a bug they found before testing [hydrogenaudio.org].

Too bad, too. I would've loved to have seen how it compared.

Error bars

As a physicist, I'd just like to draw everyone's attention to the error bars on these charts. For the majority of the tests, it's possible to draw a horizontal line through the 95% confidence intervals of nearly all the points.

Hence, the conclusions declaring clear winners/losers in these cases are invalid. If 99% confidence intervals were used (which gives a better statistical test), I feel that no clear winners or losers would be drawn.

Be careful with these sort of studies - even though the author has used confidence intervals, he has failed to use them to infer the proper conclusions.

That said, it's awfully nice to see error bars on this sort of website. Simple data points give such a false sense of precision, I find...

Re:Error bars

As a high school senior in a Statistics AP class currently studying confidence intervals and hypothesis testing, I think you are missing something. At the beginning, he clearly states your point: "One codec can be said to rated better than another codec with 95% confidence if the bottom of its line segment is at or above the top of the competing codec's line segment." The author gives which one is in first place, but announces at the beginning the requirements for a clear winner. And the author seems to me to be requiring at least half an interval of difference to even say that, much of the time he says they are tied.

Perspective

Not to quash anybody's personal opinion of AAC, there are a few things that we should note.

1) Most people can't tell the difference between formats that are similiar in performance.
2) Some people actually can tell the difference.
3) Some people are just posers who can't tell the difference but say they can.
4) Lastly, most people don't really care as long as it is convenient to use either format.

Sounds good to me

I had all of my CDs ripped to 192kbps MP3. When iTunes came out with AAC, I did a bunch of rip testing. I ripped from Donald Fagen's The Nightfly in a bunch of formats and bitrates. I found, for my personal preference, that 128kbps AAC was at least as good as 192kbps MP3, if not better. So I reripped all of my CDs to 128kbps AAC and got more songs onto my 5GB iPod. Now I'm on to ripping all of my old vinyl to AIFF, eventually to end up as AAC. Huzzah!

Re:Sounds good to me

I found,

for my personal preference, that 128kbps AAC was at least as good as 192kbps MP3, if not better.

This statement irks me to no end. Your wording is better than most others though as you used for your preference.

The thing to remember is that MP3 and AAC are different encodings. Comparing AAC to MP3 (to OGG to WMA...) is not like comparing MP3 algorithms. AAC will throw out different sounds that MP3 will keep, and vice versa. For example, a symbol crash sounds a lot better on an MP3 than it does on a similarly encoded AAC (I use LAME MP3s and iTunes AACs, they might sound different on others). However, vocals are clearer on AAC than MP3. I find overall AAC is superior to MP3, and that's what I have my songs as. However, saying a 192 AAC == 128 MP3 is a bit faulty. Both have their strengths and both have their weaknesses.

AAC vs. AAC not the issue

Most of the complaints I've heard registered about the iTunes Music Store 128 Kbps format isn't that it sounds like crap compared to other AAC implementations. The major complaint is that it not only falls far behind Apple's claim that it sounds indistinguishable from the original lossless CD, but it also fails to sound even as good as MP3 with a decent encoder like LAME using --alt-preset standard or OGG at medium quality.

I understand Apple trying to keep filesizes to a minumum, but in these days of 3.0 Mbps DSL links to people's apartments and storage prices at absolutely mind-boggling low price points, their logic is becoming less and less understandable with each passing month.

AAC actually sounds like a well-developed and efficient lossy format but let's up the bitrate a bit especially when the price of a physical CD with all the artwork and liner notes along with lossless tracks and the ability to rip them to a lossy format for portable use is only a few dollars more, and in some cases the same price, than an album on the iTMS.

Do you ask a car mechanic...

For the chemical formula for internal combustion? No. Likewise, I wouldn't go to the local audiophile shop to ask them about audio engineering-related issues. After being accosted by about ten salespeople in ten minutes at a local audio store that sells everything from Sony ES, to Krell, Wadia, Sunfire and the like... I caught a sales rep in a bold-faced lie. I was looking for a receiver without many bells and whistles, and he tried steering me towards Denon. When I asked why Denon is "better", he replied, "Because they focus solely on making audio components unlike Sony." I chuckled and asked him to explain to me the funadamental difference between the sample & hold buffers on a Sony DAC vs. a Denon DAC... Naturally, he had no clue what I was talking about. The "double-blind" survey is somewhat misleading... but that being said, it's clearly not measuring which format is superlative... it's only measuring people's perceptions. And people were pretty much even on those various formats. The study in question just shows that people cannot consistently tell the difference between AAC formats. Now, I've read articles in audiophile magazines that insisted that SACD (Super Audio CD) was brilliant in comparison to CD. And every one of those articles was a load of crap. Fundamentally, even the most "discriminating" audiophiles cannot tell the difference between 16-bit, 44.1kHz PCM (Pulse Code Modulation - e.g. AIFF, WAV, in the computer world) and the 1-bit, 2.7GHz DSD bitstream of SACD... nevermind the minute differences betweeen various AAC-enabled codecs. Hell, I would challenge anyone to be able to tell the difference between 16-bit PCM and MPEG-4 AAC. The AES (Audio Engineering Society) has stated that MPEG-4 AAC is perceptibly indistinguishable from uncompressed 16-bit, dual channel PCM (e.g. CD-DA spec audio).and I would wager any experienced audio engineer's pair of ears (my own included) against any consumer "audiophile" any day of the week. My advice to the idle rich? Don't buy the $45,000 pair of speakers... instead buy yourself better hearing and some common sense. My personal preference? MPEG-4 AAC. As a content creator intensely familiar with a variety of media standards including AES, NTSC, ISO, ITU-R/CCIR, etc. I believe MPEG-4 w/AAC (not Quicktime MPEG-4, mind you, but straight MPEG-4) is the superlative format for compressed audiovisual media. However, for critical listening, only uncompressed audio is the way to go. The general rule of thumb is that higher bitrates are preferable over higher sampling frequencies. Frequency response roll-off is what you want to avoid. But in order to support the higher bitrates, you need a D/A Converter (DAC, Digital-to-Analog Converter) with an effective sample-hold buffer that can crunch the necessary data to make an accurate conversion of the digital source. That being said, I'm going to begin digitally remastering my own compositions soon... and go straight from the 24-bit master to a 24-bit multichannel DVD-Audio format. Why? Even an audiophile deafened by the sound of their money burning a hole in their wallet can actually tell the difference between my 24-bit master recordings and the dithered 16-bit CD audio.

Re:Do you ask a car mechanic...

All the "formats" sound the same when played through my fairing speakers on my motorcycle - at 75mph...

However, when I am in my car playing them off my iPod->TapeDeckConvertor, well - all the formats still sound the same.

At home on my expensive stereo, I can easily tell the difference between CD and AAC. The AAC is the one playing off my iPod, and the CD is stored in a corrigated box in the basement...

How do these findings compare with mp3, wmf, etc?

I would like to see a graph or two comparing AAC, MP3, WMF, and OGG.

Look at Roberto's previous listening tests

You might find the graphs for a previous listening test [rjamorim.com] interesting if you want to see how AAC stacks up against other codecs.

Which 78s sound best, RCA or Columbia?

I have to admit to being puzzled as to why people spend so much time and energy trying to determine the relative merits of lossy formats.

I find the music I've downloaded from iTMS perfectly acceptable; ditto the music I hear on my car's factory-equipment FM receiver. That doesn't mean I can't tell the difference between them and better sound.

Actually, I've been transferring my LP's to CD... and recently I've been converting the CD's to .mp3 format with iTunes. The first recording I compressed, using some middle-of-the-road "high-quality" setting, happened to be a recording I liked because of the warmth of the violins. Remember, this is an old LP... digitized on a $250 consumer-grade CD recorder. To my utter astonishment, I could instantly tell the difference. After some experimentation, I upped everything to the max, encoded at 256k bits/second... and could still tell the difference.

On the other hand, with popular music (e.g. the Beatles) and some classical recordings, I couldn't.

The point is, if I can hear the difference between a CD and an .mp3 at 256k bits per second, that tells me that the difference in quality is NOT in some rarefied, golden-ears, territory. It's like the difference between a CD and FM radio.

So, why even bother to agonize over minute differences in an imperfect format when a) upping the bit rate does far more to improve quality than fussing over which format is best; b) the mileage varies so much depending on program material; c) they're obviously inferior to CD sound to begin with?

Isn't it a little like arguing over which electrically-recorded 1950s 78's sound better... RCA or Columbia?

Its all about the file size

People agonize because they want the best quality / size ratio. for example if aac encodes at 128 Kbps as well as mp3 at 192 Kbps you can fit more tunes on you harddrive in the same space and be happy. This isn't critical on computers with they're large hard drives, but for portables] players it matters. People also don't want to rip all there CDs multiple times.

In someways your right, people should pick a bit rate/format that works for them and not worry about it. but this is slashdot..

Don't use ANOVA here

In this analysis he presents the results of an ANOVA (Analysis of Variance). This reminds me of the saying: "If your only tool is a hammer, every problem looks like a nail". The tool the author is using is ANOVA and so he is trying to force the data into that form. Hovever, the assumptions of any ANOVA is that the data is independent, normally distributed, and has constant variance. The response ranges from 1.0 to 5.0. I haven't taken the test myself and do not know if users were allowed to select non-integer values or not but even if they were we can see from the graphs he does present that most of the responses were near the upper bound of 5.0. This type of response is clearly not normally distributed. ANOVA is faily resistant to departures from normality but one would need to fully explore the degree of the departure before placing any weight to the confidence intervals presented. My gut feeling here is that it is highly skewed and will present confidence intervals smaller than what they should be (data is forced to be artifically close due to the upper bound and having so many people report values close to that upper bound). The data can probably be viewed as independent but it must be recognized that this is an assumption. Constant variance departures may be a problem as higher responses are less variable than middle responses (due to the upper bound again). It would probably be much better to use a non-parametric test alternative to ANOVA such as a Kruskal-Wallis. Scope of inference: This is not a random sample from any population and as such cannot be interpreted to represent anything more than the perceptions of the respondants themselves. -chris

the comments

"Easy Listening

Results: iTunes wins, with Nero closely behind it, more or less tied. Faac is tied with Nero, and Compaact! and Real are tied just below Faac."

"House (Electronic/Techno)

Results: iTunes and Nero tied at first place, Real and Compaact!tied with Nero, and Faac tied to Real and Compaact!."

They were like that. Did we really need a play by play? Did he think we wouldn't be able to "decipher" these "complex" graphs?

...

Minor Detail

Just a minor detail to mention here. Dolby licenses [vialicensing.com] two different versions of their AAC codes. iTunes, when encoding for end users, uses the Dolby Consumer codec (affordably licensed by Apple in Quicktime 6). The Itunes Music Store uses the Dolby Professional codec (which would not be affordable to license in iTunes). Thus, AACs coming out of the iTunes Music Store have a higher quality at the same compression rate than the same songs you rip and convert on your own copy of iTunes.

Objectively comparing formats

These kinds of tests comparing codecs always seem to be something involving playing two versions of the song and asking someone which in their opinion sounded better. Isn't there a more quantitative way to measure the effect of the lossy compression? For instance:

1. Start with the digitized CD recording
2. Make a copy of it
3. Compress the copy with the codec to be analyzed
4. Do a lossless uncompression of the MP3 or whatever it is back to CD-resolution
5. At each sample point (44k per second) on the resulting track, compare the 16-bit sample value of the compressed-and-back version to the control version.
6. Sum the absolute value of the differences across all sample points.

In other words, whichever codec introduces the least error into the track in a closed loop encode and decode test did the best job of faithfully reproducing the original signal. No subjective human testing required. You might have to tweak it a bit (say, sum the squares of the error or something) but would an approach like this work to settle the codec debates, or is there a fundamental flaw in this technique?

Whoa there! Look at the error bars...

I have looked at these sorts of test results before, and used to take them as the truth. That was before I started taking a Design of Experiments grad class, and have some evidence to the contrary. For what it's worth, I'm the top performer in the class right now.

The issue I have is with the error bars. These are the vertical lines above and below the mean of each encoder. Like the beginning of the report says, "One codec can be said to rated better than another codec with 95% confidence if the bottom of its line segment is at or above the top of the competing codec's line segment." This is very much true for these sorts of statistical tests -- if the error bars overlap, that indicates that the means of the two groups are statistically identical. One could always adjust their confidence interval to a lower percentage, but 95% is quite often the standard.

Note how many of the plots in this test have overlapping error bars. In the first plot, for example, all of the encoders tested have overlapping error bars. The results drawn from this plot should be that no encoder was measurably different than any other encoder -- not that iTunes won, like the results say. (Note: I own a Powerbook G4, and am typing this post on it right now, and I love Apple. I just don't like bad statistics, that's all)

The results given in many of the plots are based strictly on the means of the samples, and not the error bars, which are actually more important in this case. Do not trust them. Interpreting the plots with the logic stated at the beginning of the article is the only statistically sound method (that I know of). I hope this sheds some more light on these tests...

It's all quite ridiculous

All this fussing over miniscule differences in quality is plain stupid. I'm yet to hear a stereo system that could make me think that the performers were actually in the room with me - or even come close (at least for reproductions of acoustic material - electronically generated sounds can of course be reproduced convincingly). This is like arguing over which of two different lumps of shit is actually the better gourmet meal.

Re:iTMS music does NOT sound lossy

Absolute rubbish.

Maybe you don't understand the nature of the tests?

FWIW, with the Norah Jones track 'Creepin In' (not used in this test) I can not only ABX every codec bar musepack, I can also spot the aac and mp3 variants because of the way they degrade.

Being a medical student, I assume you understand basic psychoacoustic principles?

Re:iTMS music does NOT sound lossy

FWIW, with the Norah Jones track 'Creepin In' (not used in this test) I can not only ABX every codec bar musepack, I can also spot the aac and mp3 variants because of the way they degrade.

Did you calibrate the flux capacitor?

Re:AAC is an aberration that should go away

I have to admit i'm surprised that aac was considered worse than mp3 at these bitrates.

I'm sticking to musepack. I've got 23000+ tunes (1700 albums-ish) on my home server, but can only casually find ~4-5 tunes which seem degraded from the original. Hardware support would be nice, though.

Re:iTMS music does NOT sound lossy

I can tell you're a medical student and not a doctor, because most doctors are much more realistic about the limits of their knowledge. "Scientific" limits on the capabilities of biological systems are often wrong because of some overlooked or unknown factor.

A famous example of this is that for many years scientists could not work out how bees could fly. Their wings were too small, muscles too weak and bodies too heavy. It turned out that bees were able to use previously unknown aerodynamic effects to generate more lift than our previous "knowledge" allowed. Another example is that many birds of prey have visual acuity better than the laws of optics, applied to their eyes, would seem to permit. It turned out that the visual signal processing in their brains is so advanced that birds can actually 'see' features that are below the resolution limit of their eyes.

Similarly, we shouldn't be too dogmatic about what humans can and cannot hear. MP3s (and presumably AACs) compress music by suppressing parts you "can't" hear, not because they're outside your range of hearing but because the brain, assuming those parts should be there, fills in for them even when they're absent.

But it may be that you can't hear something consciously but still tell that it's not there.
For example, there was a news story a week or so back showing that people could somehow tell when a picture had changed by the removal of an item in it, even though consciously they could not explain what the difference was - it just 'felt different'.

So, if someone claims to be able to tell the difference between 1 128Kb AAC and a CD, test that claim in a double-blind experiment. Only when he fails the test can you say he was imagining things.

I'm not a doctor, but I play one on television

It's either that, or "Damn it, Jim, I'm a doctor, not an audiophile!"

It is clear you have no idea what you are talking about. Just because you can't tell the difference does not mean others can.

The people who are "able to tell" just happen to have more sensitive hearing. I'm probably not one of them, but I have known several, including someone who cannot listen to CD's because there is a whine on all of them associated with the digital nature (this same guy does not like going into Radio Shack because of the noise made by their security system.)

Just because you are not a sensitive-eared audiophile does not mean everyone has the same cloth-ears as you do.

Re:I'm not a doctor, but I play one on television

The people who are "able to tell" just happen to have more sensitive hearing. I'm probably not one of them, but I have known several, including someone who cannot listen to CD's because there is a whine on all of them associated with the digital nature (this same guy does not like going into Radio Shack because of the noise made by their security system.)

I'm getting sick of hearing about how Jimmy the cat boy can't listen to CDs, so the rest of the Budweiser crowd has to bow down to his codec choices.

These people are either freaks who feel the need to expound their superiority at any given chance, or audiophiles who feel they're somehow making a difference by making us waste storage space.

At some point you have to choose whether you're listening to the music or the technology used to reproduce it.

Re:I'm not a doctor, but I play one on television

The parent to this post was modded down for being rude to the grandparent, I suppose... but the point was correct. "The Digital Sound," as we used to call it back in the 80s, turned out to be the result of poor D/A conversion, poor error correction, and amplification hardware that was tweaked to compensate the shortcomings of LPs. Like I mentioned on another audio-related thread last week, a $300 Rotel CD player connected to a modern high-end stereo will sound as good or better when compared to a $3000 air-suspended, laser-guided turntable. (Especially after the LP has been played a few dozen times.)

Re:I'm not a doctor, but I play one on television

I used to think the same way as your friend, because in the 80s and early 90s there did not seem to be any chance that digital sources could sound as good as my favorite LPs.

Then I heard what good CD players can sound like, and realized that the harshness of CD audio had nothing to do with resolution, and everything to do with component makers cutting corners. Your friend might make the same discovery, if he goes to a good listening room with an open mind.

Re:You may have a point

They may be pricks (or trolls), but they have some good points. If you can get past the annoying exterior, you might find some good information on these issues by googling for "audiophile" in rec.audio.pro, a group populated primarily by very good recording engineers. These are guys (mostly) who got where they are through both excellent (and aesthetically attuned) hearing and scientific knowledge of how audio works at every point in the signal chain. To watch them dismiss, with unimpeachable arguments and long experience, the claims of "sensitive" audiophiles can be instructive. I speak as one who has been schooled.

Re:AAC is an aberration that should go away

AAC is a standard format. Perhaps you've heard of the people that made it... Dolby? Ring a bell? Just about anything doing with excelence in audio comes from them. I can see four things in my shoebox of a dormroom that has their logo on it. I also find that most of the people that are so violently against DRM (in any form) are the people who would be analy raped by the RIAA/MPAA if they raided your house. I find that the DRM used in the iTunes store is fair, and more or less barely noticeable. Don't have a player that can play AAC? Buy one or shut the fuck up. You bought a player that doesn't do what you want it to, thats no one's fault but your own. Thats like buying DVDs then bitching because your VCR won't play them. Grow up.

Re:AAC is not a standard format

I somewhat understand your angst, but the following is a bit ridiculous:

"I find that the DRM used in the iTunes store is fair, and more or less barely noticeable"

It's far from fair, since it requires the kludgey solution of burning to CD and then ripping to an actual usable format in order to make use of your OWN files on your OWN machines.

If you got a track from iTMS, you MUST have downloaded it with iTunes. Thus, you have a solution for using the original file on your machine (Windows and Mac). Don't complain about the lack of Linux support. It's apple's baby and they can do what they want with it.

I'm not saying you have to like AAC, or support its right to exist, but if you knowingly buy an iTMS track, caveat emptor.

Also, I'd like to know what rights Fairplay has denied you? The right to share music with all your friends? Copyright law already forbids that. Fairplay only enforces it. Your example of AAC to CD to MP3/WMA/etc. claims that you have lost the right to directly convert AAC to another format. I hardly find that overly restrictive, considering the alternatives (only one machine, only one portable music player, limited times burning the track, etc.)

Audiophile opinion

I used to work for an auto electronics installer, and the most discerning fuckers would pay out the nose for single directional cable which sounded JUST that bit better.

I used to get my jollies installing the cable the wrong way round on one side. Not one of the audionerds noticed by listening.

Want to know how much flowery crap they can go on with? Take a look here [netsuite.com]. You only have to read the descriptions of a few of those turntables to realise these guys are as wacked out as alien abductees and the guy on the street corner who tells you every morning he has the FBI after him.

Re:Audiophile opinion

Ha! The audiophiles are nutters, it's true.

But this is different. Bear in mind 'CD quality' ('Red Book' audio) has been established as a base line for the last 10 years or so. Lossy compression degrades this quality by variable amounts depending on what codec is used, what the source material is and at what bitrate it is compressed. The reason for so much development on these codecs isn't to find an audio nirvana, but to minimize the loss from the source material.

Re:Audiophile opinion

Oh there's definitely a difference in pure analogue vs cd quality vs lossy compression codecs. Just taking a compression ratio down to 96kbit will make most listeners wince when their favourite tracks are played

I think that's part of it for many people. We might not hear parts of the music just like we may not "see" parts of a video clip on the first run round, but after 3 years listening to Louis Armstrong direct from CD, hearing him on 128kbit MP3 can be harsh. Humans learn and learn well, and the repitition of that playing guarantees we'll hear things that we're not meant to! or rather, things that we don't need to in order to identify a particular artist and recording. But we don't just listen to something to identify it, we listen to enjoy. That's different.

Most of the time 128kbit is fine for me. 192kbit for the things I'm familiar with.

Re:Audiophile opinion

Actually, frequent listening will make your brain better at filling in the data which isn't there. For example: watching DVDs use to bother the heck out of me whenever diffuse lighting created that "layered" effect. Now I hardly ever notice it unless it's ultra-obvious (as with 2001 or some film noir movies), or I'm actively watching for it. My mind usually just interprets it as light fading to darkness now.

The better you know a subject, the more clearly you can "see" it through a dirty window.

P.S. Most of Louis Armstrong's best stuff was recorded on very harsh-sounding "clay 78s." No matter what format you play his Hot Fives and Hot Sevens singles on, it's going to sound like mush. This is another example: People who listen to a lot of live jazz have no trouble listening through all the ticks, pops, scratches, microphone clipping, bad accoustics, etc. and in their "mind's ear" can hear just how brilliant and beautiful Armstrong's recordings are. Those who don't can barely make out a fuzzy-sounding trumpet in an echo-filled hall, and wonder what all the fuss is about.

Re:Audiophile opinion

pay out the nose for single directional cable

Ha ha ha! I love the directional cable talk!

As soon as you find someone who starts talking to you about directional audio cables, you must do two things: discount anything else they have ever said to you, and laugh in their faces. While it may seem, to the uninformed, that music 'flows' from the CD / record player out to the speakers, we must always remember that speakers are AC. Alternating current is required to make the speaker cones move in and out.

The real problem is that with all that back and forth motion, the electrons can get very very tired. I recommend that everyone with directional cables should only play their scratchy old LPs for a few minutes each day, lest the electrons in their very expensive cables succumb to extreme fatigue. Come to think of it, the Golden Ear crowd better buy replacements for all their cables once a month -- just in case!

Re:iTMS music does NOT sound lossy

Bollocks! BUT...

If I listen to an MP3 or AAC file on my computer with its sound card and speakers (SB Audigy, Boston Accoustics) I can tell the difference between the same (160kbs) MP3 file and a (128k) AAC - the AAC sounds better. I can't tell the difference between the AAC and a WAV file however.

If I move up to my ($$$$) home stereo then I can easily tell the difference between the compressed and non-compressed versions of the same song. AAC still sounds better to me than MP3 however.

The difference here is money and environment, my office is a noisy place with all the computers etc running. My listening room is quiet and I spent a lot of time setting the stereo up so that its at its best.

I have not looked at OOG or any of the other formats so I can't comment on the relative merits of them.

Re:iTMS music does NOT sound lossy

Being a medical student who has a particular interest in this stuff, you have to know that due to compression method AAC, MP3, ATRAC, etc generates artifacts during compression.
I mean due to "harmonising".
Furthermore, there exists some "dynamic range compression"
So I have to tell that:
a) if you are listening in APPROPRIATE conditions and on APPROPRIATE sound system (mean amplifyer&speakers&QUET room) you easily can distinguish compressed from flat by dynamic range. Possibly you can't tell what's difference is, but you CAN hear it.
b) it's not so hard to generate a soundwave that will compress very bad (you easily can point difference) at any bitrate.

Example: get audiotest CD, compress it, listen to what you get.

Re:iTMS music does NOT sound lossy

This only means that you don't have a good enough stereo!