How Good Is AAC?

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Well, reviews are coming in from real people about the products from Apple’s music store, and the results are mixed. Pick the opinion you want, and you’ll be able to find it.

While audio folks can be even wackier and geekier than computer folks (with a big snob element to boot), the consensus seems to be that AAC does a bit better than MP3 at the same bit rate. That’s the good news.

The bad news is that the better your sound system, the worse it will sound, just like MP3s. These files are no substitute for CD tracks.

Compression on Compression

Most people know that formats like MP3s and AAC (which, btw, wasn’t invented by Apple, it was invented by Dolby) compress the size of files by reducing the amount of musical information in the file, then reconstructing an approximation using computer algorithms.

What not so many people know is that CDs themselves operate on the same principle. Not all the available musical information gets on a standard CD; it can’t. CDs are digital, not analog; it can record only instants in time.

This is why you hear terms like “sampling” used. A CD doesn’t record everything like a vinyl record; it just takes a lot of samples (44,100 per second on a standard CD) of the available information, and then uses the same kind of algorithms in its DAC (Digital Audio Converter) to connect the audio dots.

CDs also use 16-bit sampling. This determines the dynamic range (difference between the softest and loudest sound) of the recording.

Recently, there’s been a move to audio standards that increase both the sampling rate and the bit size. These standards go from the CD standard 16-bit/44,100 samples per second standard to 24-bit/96,000 samples per second.

More information means bigger files.

If you are looking at MP3s/AAC recorded at 128kbit/sec, we’re talking about roughly a megabyte a minute.

For MP3s/AACs, The data rate scales linearly with bit rate, so a 256kbit/sec rate would be about two megabytes a minute

If you’re talking about standard CD sound, we’re talking about roughly ten megabytes a minute.

If you want to sneak a peek at 24/96, the price for more musical info rises to over thirty megabytes a minute.

What’s Good Enough?

There’s no easy answer to this. The answer depends on a mix of these factors:

How Hard Is Your Music?

This webpage illustrates one big problem with compression. The author of this website was experimenting with lossless compression (like what you have with .zip files).

At the bottom of the page, you see a chart in which various songs and sounds were compressed, and how much they could be compressed without losing data. What you’ll notice is that different songs have much different levels of tolerance for compression.

If you look back at the data rates earlier in this article, you’ll see that typical MP3 sizes are a tenth the size of typical CD files, which is a compression ratio higher than any actual sound pattern could tolerate without loss.

So you lose something no matter what. Does it much matter? From a soundwave perspective, the more complex (and less predictable) the music, the worse it will generally sound compared to the original, simply because the DAC has more work to do, and relatively less to do it with.

How Good Is The Audio Equipment?

Lousy sound and lousy audio go great together. If you can’t hear all of what’s there anyway, you don’t miss what isn’t there.

This works until you move up the world audio-wise. The standards in your head go up once you hear better sound and better audio. That’s why people sometimes complain that some records don’t sound as good on a better system. The recordings haven’t changed, they have.

How Good Is Your Audio Equipment?

People have different abilities to listen. Some have better hearing than others. Some either naturally or through experience listen more closely and notice more things than others.

How Sensitive/Irritable Are You?

How people react to music is much like how people react to computer noise. Some people don’t even notice. More notice, and would prefer less, but they can easily tolerate some. Some are (or get) extremely sensitive to it, and get (at least to the less sensitive) fanatical about getting rid of it.

It’s pretty much the same with music. What can be literally painful and agonizing for one person may not even be noticed by another.

Conclusion

This is a highly subjective experience. If you’re looking for a quick-and-dirty test to see whether you’ll like what Apple has to offer, do the following:

The files Apple is offering are the rough equivalent of 160kbit/sec MP3, so on average, they’ll sound a little bit better than 128kbit/sec MP3s and a little worse than 192kbit/sec MP3s.

Is that good enough for you?

If you don’t know already, rip some of your own music CDs and listen to them wherever you’d listen to them (computer, car, home stereo).

Is what you hear good enough for you? Before you answer “no,” ask yourself if CD quality is worth ten times the space per song (or put another way, would better quality be worth one-tenth the number of songs you can put on your MP3 player)?

Whatever you come up with is your answer.

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