Audio compression may not be so bad

Our tests with music professionals found that they had a hard time distinguishing between compressed and uncompressed songs

We all listen to compressed music on our computers and portable players and we all know that compression is supposed to hurt sound quality. But does it hurt it enough to affect our listening pleasure?

I tested the effect of compression with a jury of music professionals and the results surprised me. Although the type of compression had a definite effect-my judges preferred .wma to .m4a and .mp3--the level of compression had little effect on how they rated sound quality. Most importantly, none of the compressed music sounded really bad to their well-trained ears.

The most common consumer audio formats--.mp3, .wma, and .m4a--all use lossy compression that throws away musical nuances to cut download times and fit more songs on our players. For instance, if you ripped Dire Straits' album Brothers in Arms to your hard drive as uncompressed .wav files, they would take up 556MB of space. You couldn't fit 15 albums of equal length on an 8GB iPod Touch. But as .wma files, compressed to 160kbps, the whole album is less than 64MB, leaving room for 127 similarly-squeezed albums.

Many people say they can hear the difference between music compressed at different levels, but their experiences could be shaped by their expectations. They know they're listening to a highly compressed song, so they blame the compression for every real or imagined flaw.

To get a less biased judgment, I set up blind audio quality tests. A jury of musicians rated various compressed samples on how closely they resembled the original.

Sound Methodology

You should consider my results to be anecdotal, not definitive. I only used two recordings and four jurors--hardly a scientific sample size. Besides, this type of test is inherently subjective; people respond to what they like.

I ripped two 30-second clips from CDs for tests. One came from the first movement of Tchaikovsky's sixth symphony, performed by the London Symphony Orchestra, with Igor Markevitch conducting. The other came from Joan Osborne's cover of Bob Dylan's "Man in the Long Black Coat."

I saved seven versions of each clip. To test music formats, I saved the clips with 128kbps compression in the three most popular formats: .m4a (which uses aac compression and is what you get from iTunes), .wma (Microsoft's format), and the old standard, generic .mp3.

To find out how compression levels (as opposed to formats) affected audio, I also saved .mp3s at 192, 256, and 320kbps. The larger number means less compression and, in theory, better sound. I also saved the clips as uncompressed .wav files.

[Want to try a portion of this test? We've set up a page with versions of both clips at different compression rates. (You'll need to have Quicktime installed.) You can listen and tell us what you think the quality is of each clip. SPOILER ALERT! Hold down the Control key as you click the link, then wait a couple of minutes before you go the new tab. The less compressed the file, the longer it takes to load, so if you see the page load, you'll get an idea of which files are high quality. Click here for the test.]

I played the uncompressed .wav file, then a compressed version, and asked the jurors to grade the second sample compared to the original. For one test, I played the uncompressed original twice, without the jurors knowing they were listening to the same file twice to see if they could detect the high quality .wav version.

I played the files using my Lenovo X60 laptop, connected to my home theater sound system with a Yamaha RX-V465 receiver and satellite speakers and a subwoofer from Cambridge Soundworks.

I instructed the jurors to grade the audio from 5 ("sounds identical to the uncompressed original") through 1 ("unacceptable"). Decimal numbers were allowed, and comments encouraged.

Tags audio compressionaudio codecsMP3

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

Lincoln Spector

PC World (US online)

Comments

Comments are now closed.

Most Popular Reviews

Follow Us

GGG Evaluation Team

Kathy Cassidy

STYLISTIC Q702

First impression on unpacking the Q702 test unit was the solid feel and clean, minimalist styling.

Anthony Grifoni

STYLISTIC Q572

For work use, Microsoft Word and Excel programs pre-installed on the device are adequate for preparing short documents.

Steph Mundell

LIFEBOOK UH574

The Fujitsu LifeBook UH574 allowed for great mobility without being obnoxiously heavy or clunky. Its twelve hours of battery life did not disappoint.

Andrew Mitsi

STYLISTIC Q702

The screen was particularly good. It is bright and visible from most angles, however heat is an issue, particularly around the Windows button on the front, and on the back where the battery housing is located.

Simon Harriott

STYLISTIC Q702

My first impression after unboxing the Q702 is that it is a nice looking unit. Styling is somewhat minimalist but very effective. The tablet part, once detached, has a nice weight, and no buttons or switches are located in awkward or intrusive positions.

Latest News Articles

Resources

Best Deals on GoodGearGuide

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?