The Psychology of Compressed Sound: How Compression Affects Music Perception
As we delve into the world of modern music, it's impossible to ignore the significant changes in sound quality over the past decade. One of the most dramatic shifts is the increased loudness, a result of dynamic compression. But there's also another type of compression at play: digital compression, which allows us to store vast music libraries on portable devices. Let's explore how these compression methods impact our perception of music.
To determine the effects of frequency compression on music perception, it's important to consider the impact of previous music training and hearing status.
Dynamic Compression: The Loudness War
Dynamic compression is a technique used extensively in popular music to make the quiet parts louder and the loud parts quieter. This process aims to make the music "jump out" of radios or iPods. However, it can significantly alter the sound, as Bob Ludwig, a mastering engineer with over 40 years of experience, explains.
Ludwig points to a YouTube video titled "The Loudness War," which uses Paul McCartney's 1989 song "Figure of Eight" to illustrate the difference between the original recording and a modern, compressed version. "It really no longer sounds like a snare drum with a very sharp attack," Ludwig notes. "It sounds more like somebody padding on a piece of leather or something like that."
The "Loudness War" reached a critical point with the release of Metallica's album "Death Magnetic." According to Ludwig, 10,000 or more fans signed an online petition to get the band to remix the record. "That record is so loud that there is an outfit in Europe called ITU [International Telecommunication Union] that now has standardization measurements for long-term loudness," he says. "And that Metallica record is one of the loudest records ever produced."
The motivation behind this loudness increase dates back to the days of 45s. Producers wanted their records to sound louder than others to catch the attention of radio program directors. While this goal remains for some, Bob Ludwig believes it's an unfortunate trend. "People talk about downloads hurting record sales," Ludwig says. "I and some other people would submit that another thing that is hurting record sales these days is the fact that they are so compressed that the ear just gets tired of it. When you're through listening to a whole album of this highly compressed music, your ear is fatigued. You may have enjoyed the music but you don't really feel like going back and listening to it again."
Subjects generally preferred the conditions with the lesser amount of compression. Although less frequency compression was in general preferred, there was more variability in the comparisons involving the default settings for a 50-dB hearing loss.
Old News "The 'Loudness Wars' have gone back to the days of 45s," Ludwig says. "When I first got into the business and was doing a lot of vinyl disc cutting, one producer after another just wanted to have his 45 sound louder than the next guy's so that when the program director at the Top 40 radio station was going through his stack of 45s to decide which two or three he was going to add that week, that the record would kind of jump out to the program director, aurally at least."
Bob Ludwig thinks that's an unfortunate development. "People talk about downloads hurting record sales," Ludwig says. "I and some other people would submit that another thing that is hurting record sales these days is the fact that they are so compressed that the ear just gets tired of it. When you're through listening to a whole album of this highly compressed music, your ear is fatigued. You may have enjoyed the music but you don't really feel like going back and listening to it again."
Ludwig's final assessment of the decade in music? "It's been really rough, folks," he says. "But it can get better and I think it will get better. I'm glad it's going to be over."
Digital Compression: Convenience at What Cost?
Digital compression is the process that reduces the size of a sound file, allowing us to carry thousands of songs on devices like iPods. However, this convenience comes with potential drawbacks in audio quality. Dr. Andrew Oxenham, a professor of auditory perception at the University of Minnesota, explains the process.
"Really, the challenge is to maintain the quality of a CD, but to stuff it into a much smaller space," Oxenham says. "Let's think about how digital recording works. You start out with a very smooth sound wave and we're trying to store that in digital form. So we're really trying to reproduce a smooth curve [with] these square blocks, which are the digital numbers [the 1s and 0s that are used to encode sound digitally]. Now, the only way you can make square blocks look like a smooth curve is by using very, very small blocks so it ends up looking as if it's smooth. Now using lots and lots of blocks means lots of storage, so we end up using [fewer] bigger blocks. Which means we end up not representing that curve very smoothly at all."
"The difference between the smooth curve and the rough edges you end up with in the digital recording, you can think of as noise because that is perceived as noise," Oxenham says. "It's perceived as an error, something that wasn't there in the original recording. The trick is to take the noise - which is the loss of fidelity - and just make it so you can't hear it anymore."
Masking: Hiding the Imperfections
This process of hiding the noise is called "masking." Oxenham explains it with an analogy: In a quiet room, you hear every detail of a conversation. But in a noisy environment, like a busy street, you only catch the gist, missing some words due to the traffic noise masking them.
Similarly, in music, the loud parts of a recording can mask the noise produced by the rough-edged squares of digital encoding. "[The loud parts of the music are] giving the coding system a lot of leeway to code things not quite as accurately as it would have to," Oxenham says, "because the ear is being stimulated so much by the loud sound it won't pick up very small variations produced by the coding errors."
But are we missing something? "There are really different levels of MP3 coding," Oxenham says. "You can go from much less data - which people can hear the difference - to higher levels of coding which take up more space on your MP3 player but sound better and are basically indistinguishable from a CD. And I would argue that under proper listening conditions - if it's really indistinguishable from the CD as far as your ear is concerned - then you really haven't lost anything perceptually."
Oxenham likes the convenience of portable MP3 players.
Christopher Clark's visual analogy for dynamic explains in part why music sounds worse now.
Dynamic Range Compression