Can You Really Tell the Difference Between Music at Different Bit Rates?

(Note: this article is written for Mac users. If you have Windows tools to recommend, please mention them in the comments.)

The bit rate debate regarding compressed music is one that will be around for a long time. Some people think that any compression of music files is anathema. Take Neil Young. He complained about the poor quality of digital music files, while greatly misunderstanding much of what is involved in compression. He claimed that only “5 percent of the data present in the original recording” is present in MP3 files, without specifying the bit rate used or the original sources, and without understanding that compression is more than just lopping off bits of the music. (Andy Doe, writing on the Naxos Blog last year, published an article, All About Bitrates, explaining how compression works. You should read this to understand some points that most people overlook.)

When you start ripping music, and decide what bit rate to use, you have several options. You could go for lossless, which compresses music around 40-60%. One advantage to this is that you can then re-convert the lossless files to a lower bit rate if you want, keeping the originals as archival copies. But lossless files take up much more space. While this isn’t an issue on computers – hard drives are huge these days – it is for portable devices like iPods or iPhones.

If you don’t use a lossless format, you have to decide which format to use (AAC or MP3), and what bit rate. For a long time, Apple sold music at 128 kbps at the iTunes Store. It is now 256k, which is roughly what Amazon uses in their MP3 store (their music is in VBR, or variable bit rate, so it is not exactly 256k). This is an excellent compromise between space and quality. But you might want to go even lower. What’s important is to find the point at which you cannot hear the difference between an original file and a compressed file, and stay above that bit rate.

To do this, you need to perform what is called blind ABX testing. You are presented with music and don’t know which bit rate you are hearing, and you must choose whether you think it is compressed or not. While this test takes a bit of time – you need to rip tracks at different bit rates, then test yourself, one pair of tracks at a time – the results can be interesting.

To start with, find several songs or tracks that you know very well. It’s best to use familiar music, because you will be able to hear more of the differences (if any) because of your familiarity with the melodies, arrangements, etc. I’d recommend not ripping full albums for this test, but rather individual songs or tracks from different albums.

Rip these tracks from CD in lossless format. In iTunes, go to Preferences > General, then click on Import Settings. Choose Lossless Encoder from the Import Using menu.

Next, add the tracks you have ripped in lossless format and to a playlist. Select them all and press Command-I, then enter an album name, such as Lossless Tracks. You’ll want this later to be able to find them.

Back in iTunes’ Import Settings preferences, change to the AAC Encoder, and set the bit rate at 64 kbps. Yes, I did say 64 kbps; you want something that is low enough so that you are guaranteed to hear a difference. As above, create a playlist, then tag all these tracks in an album 64 kbps Tracks.

Go to the Mac App Store and download the free ABXTester. This application lets you choose two tracks, then listen five times to a random selection of those tracks, and choose the one you think is better.

Click on Select A. Navigate to your Lossless Tracks album, and select a track. Click on Select B, navigate to your 64 kbps album and select a track. You know that the first track is lossless, and that the second severely compressed.

The next step is to try five tests, listening to tracks selected at random, and choose whether you think each track is A or B; in other words, which is the better sounding track. For example, when you listen to the first track at X1, if you think it’s the lossless track, click on A; if not, click on B. At the end, click on Check answer, and see how well you did.

I suggested starting with 64 kbps tracks so you can hear a difference. The next step is to find at which point you can no longer hear that difference; at which point your results are no better than random (2 or 3 correct, or a score of 40 or 60%). Rip the same tracks at several other bit rates: I suggest you use 128, 256 and 320. If you do too many, the test will take too long. Label each group of tracks. You can now either go to the next level, 128 kbps, for track B, and go through the tests, or you can start from the other end, at 320 kbps, and work your way down. No matter what, I think you will be surprised.

A couple of notes. First, make sure you do this test on the stereo equipment or headphones you use to listen to music. (If you’re curious, these are the headphones I use.) You might find that, if you try this out on a friend’s Really Good Stereo that you might hear a difference. If you don’t plan to buy the same Really Good Stereo, don’t bother testing on it. If not, you won’t hear a difference; I guarantee it.

Of course, this begs the question: if you don’t have good stereo equipment or headphones, is it worth using a higher bit rate? If you’re thinking of upgrading your stereo or headphones, you might want to plan ahead and do this test on better equipment to see if it’s worth ripping your music now at a bit rate higher than where you can currently hear a difference. And if you have plenty of disk space, you might want to rip your music in lossless format for archival purposes, then convert it to a lower bit rate for use with your portable devices. With iTunes, you can rip in Apple Lossless format, then have iTunes convert your music files during the sync process to 128, 192 or 256 kbps.

Also, if you want to compare high-resolution files, make sure you open Audio MIDI Setup (in the /Applications/Utilities folder), and set the sample rate to the highest possible setting. Otherwise, you won’t hear the full resolution of these files.

I’d be interested to hear your results. Feel free to post them in the comments. If you can really hear a difference between a lossless file and a high-bit-rate compressed file, please also post what kind of stereo equipment or headphones you are using.