Chasing digital music's 'codec killers'

If you've downloaded a Van Halen, Hole, Sarah McLachlan or even a Beatles song online, and it sounds just a bit off to you, you're not alone--you might have run into a "codec killer."

Online music services such as Apple Computer's iTunes and MSN Music are betting that digital music sales will rival or even surpass those of CDs one day. But to serve today's market, they're forced to use audio formats--called codecs--that transform recorded songs into relatively small computer files that can be downloaded over Net connections.

News.context

What's new:
The process of transforming recorded songs into relatively small computer files that can be downloaded over the Net sometimes creates audible defects.

Bottom line:
The problem creates a challenge for digital music companies, which must ultimately convince online music buyers that computer files provide a quality listening experience.

More stories on music codecs

Most of the tricks audio engineers use to compress music into these small packages are almost wholly inaudible to the average human ear. But there are songs that prove consistently thorny for these technologists, throwing up audible defects whenever they are squeezed into Net-friendly sizes.

"You can fool most of the people most of the time, but you can't hide (flaws) all the time," said David Ranada, technical editor of Sound & Vision Magazine.

Although rare, the "codec killer" phenomenon is a potentially serious one for digital music backers. Just as the music industry had to assure consumers that the sound quality of CDs was as good as that of vinyl records, digital music companies must ultimately convince online music buyers that computer files provide a listening experience comparable to that of CDs.

Even just a few purchases of songs that wind up with defects, ranging from muddy sound to audible "artifacts"--sounds that aren't supposed to be in the recording--could turn off buyers, analysts say.

This idea of "codec killer" has been familiar to audio technologists since they started transforming audio into compressed formats. Much of a codec designers' job is figuring out how different technological tricks will interact with the ear and minimizing these ill effects.

Bleeding eardrums

Here are some "codec killers" cited by audio experts:

"Building a Mystery," Sarah McLachlan

"Celebrity Skin," Hole

"Revolution 9," The Beatles

"Everybody Wants Some (remastered)," Van Halen

"Goodbye Yellow Brick Road," Elton John

"Daughter," Pearl Jam

"Dorita," Lou Reed

Each compression technique uses different ways of packaging the data. But most modern song-squeezers essentially aim to remove from an audio wave information that won't be missed by the human ear.

Many of the tricks are based on using the ear's own physiology to fool it into hearing things that aren't really there, or figuring out which elements of a sound wave can be eliminated without substantially changing the sound. A succession of technologies such as MP3; Advanced Audio Coding, or AAC; and Windows Media Audio have gotten increasingly better at this during the past decade.

But these tricks run into problems with specific kinds of sounds.

For example, one common technique essentially divides a song into very small blocks of sound--a few dozen milliseconds, for example--and takes bits of information out of each block. The effect this has is similar to a blurry picture, smearing out the sound very slightly over time.

This effect is mostly indiscernible to all but the most trained ears. But some very sharp sounds--a wood block, or a castanet recording--often wind up with what's called a "pre-echo," or a hint of the sound before the full instrument actually begins.

That essentially confuses the ear, creating the perception of an unpleasant sound, said Microsoft audio architect Jim Johnston. He compared the ear's reaction to what the eye does when exposed suddenly to a bright light in the dark.

"Castanets are like turning on the sun at midnight," Johnston said.

Different issues create different audio artifacts, or flaws. Very pure sounds are sometimes hard to squeeze into a compressed state, in part because the same smear effect can undermine their purity. Songs that are recorded at very high volumes can prove difficult, as can songs with powerful low-frequency bass tracks.

"What's difficult for a particular codec depends on the codec itself," said Christopher "Monty" Montgomery, one of the lead engineers behind the Ogg Vorbis open-source audio technology project.

The worst effects could almost always be minimized by keeping a song in the highest quality format available, Sound & Vision' Ranada said. Changing from one compressed format into another--from iTunes' AAC into MP3, or from MP3 into Sony's ATRAC, for example--is almost always a bad idea, he said.

Even beyond the individual songs' difficulties, the prevalence of mediocre-quality MP3 songs on file-swapping networks and in personal music collections has had a damaging effect on music listening, Ranada added.

"I think people's tastes are being degraded by exposure to 128 kilobit per second MP3s," Ranada said. "If that's all you hear in your acoustical life, and never go to a concert, you'll never know what real music sounds like."

[swwg69]

We need Super CD or DVD Audio

MP3s should be like trailers or commercials.
Give them away to sell real music in good, large
file format. If you listen to DVD Audio, you
will want it. The music industry needs to push
for higher quality product and slow the roll out of faster broadband.

The CD isn't digital?

Hi -

Basically an OK article, but one really, really major faux pas: CDs aren't digital?

Uhhhh, where were you during the 1980s and 1990s when audiophiles were lambasting "digital" music as soulless and sterile in comparison to their wonderful analog LPs (and their thousands of dollars invested in hifi equipment!). Music on CDs is per definitio digital.

What you mean, I dare say, when you use the term "digital music" is music that has been compressed according to psychoacoustic standards. CDs usually aren't. That's the difference.

With psychoacoustical regards,

John

BRAVO! end crappy audio

I love portable music but can?t stand the crappy audio quality. I also love the concept of satellite radio but the dynamic range is so bad I can?t listen to it.

[CagedAnimal]

Thank you for giving this a bigger voice.

I have always been laughed at when I saw I would pay a bit more (to cover additional internet traffic costs on the suppliers end) per track for downloads in a lossless format. Most people don't notice the flaws, and I can't admit to being able to pick them an AAC track on a blind test. However, the flaws of MP3 became pretty apparent when I got a half decent stereo, and so will the flaws of any lossy codec with more listening and better equipment

I'll definetly have better audio gear someday, and the more I listen the more I can tell that the compressed tracks just aren't transparent, and that is not listening with the intent of finding defects. Why whould I be denied CD quality because I would like to buy my music by the track. Just offer downloads in lossless formats and be done with it.

[chartshark]

Catch the .wav

Even the best MP3 sounds like crap if you listen to it next to the actual song in .wav! You think .99 is a good deal for a song? Me too, but not the for part of a song you get in a download.

http://www.exactaudiocopy.org - this app. makes great rips of cd's in both mp3 and wav. Given how cheep storage has become, why not just store all your songs in wav. You can fit a boatload of songs, real songs(.wav) on a 40gb player!

Upshot to going to the record store, you might meet someone nice there and can cancel your online dating service.

[Not Bugged]

Lossless Compression

"Full Quality" does not necessarily mean "Uncompressed." There
are Lossless compression formats (Such as FLAC and the Apple
Lossless codec for iPod/iTunes) that reproduce the full content
of a CD/WAV/AIFF recording while reducing file size up to 50%.

[nah40]

real music

i do not call the crap that various artists paly at their concerts "real music"

[mcgrail]

Yes, I know some other codec killers!!

As an educator who teaches audio, I am struck by the fact that students rarely care about the reduced quality of MP3s. Many deny that there's a difference from CD's, until they're shown the difference. And yes, I laud SACD and DVD-Audio (especially the latter).

My own research has shown that certain instruments, such as the Yamaha CP-70 electronic piano, reproduce terribly on MP3. That's because it isn't just a sampled sound, but a tine-based instrument. Also, violas sound horrible. The col legno (wood sound) of the initial attack is reproduced very inaccurately.
The American public needs to be aware what a rip off ripping can be.
Give me 24 bit, 96 Khz every time!

[skeptik]

missed boat

If the RIAA were more concerned about a quality product and less concerned about litigation against their own consumer base, they would be trumpeting this fact from the rooftops. We've always known that mp3 tracks are inferior to CDs, sometimes flagrantly so.
Further, the CD is an early 80's product. Aren't we more than overdue for an update? We have the capability to distribute a vastly superior product now, and the hardware has never been cheaper. (A downside for us, but a format change and the resulting "re-buying" of standards in the new format is the single most profitable niche of business for the industry - they loved the conversion to CD, why aren't they pushing the conversion to a newer format?) But there has been no industry support, let alone push, to migrate to the superior product. Seems the RIAA would rather fight over mythical lost revenue rather than do the work to generate real revenue.
So if all they can offer is the same crappy quality I can download for free, why would I care to spend my money on their product?

MP3 is the culprit.

The mp3 codec is usually the cause to the horrible sound you usually get out of songs, and the way that an mp3 destroys these songs is by throwing out vital sound bits that give the natural sound to music, or whatever is recorded.
I've always been turned off by mp3s because of their sound, and eventually took me to lossless audio codecs like Monkey's Audio or FLAC. However, there is one lossy codec out there that is superb for the average ear, OGG - It's a open source freeware codec produced by Vorbis. The sound you usually get out of it is absolutely wonderful, as there are usually no audible audio errors whatsoever. I challenge you to take an audio CD of yours and rip it into mp3 and ogg. Listen to it in mp3 128kbps, and ogg 128kbps. You should notice a significant difference in the audio quality. And if ogg at 128 doesn't sound good enough for you, go up to 350 - if that's still not good enough, I recomend Monkey's Audio lossless codec. It has a superior compression ratio than all the other lossless codecs out there, and takes less time to encode.
http://www.monkeysaudio.com/

Good day everyone. =)