"I loved it, but they had a panic attack," Iggy said in a CD jacket interview. "It sounded like the speakers were going to explode, bleeding and melting and distortion."
These grinding walls of sound make hearing specialists nervous. That's because hearing loss depends not just on the loudness of a sound but also on its duration. An adult, for example, can listen to 85 dB noise for eight hours before suffering hearing damage but can tolerate 88 dB for only four hours.
The quiet parts of original recordings allow the listeners' ears to rest between loud parts, but heavily compressed music lacks those breaks. "It's a lot easier for people to expose themselves to loud sound now," said Sig Soli, a hearing researcher at House Ear Institute in Los Angeles.
Soli said he worries about iPod kids in particular, because their ears are still developing. "We don't know what the safe exposure level is for children," he said. "It takes a number of years to produce hearing loss, and it will take years to see the direct effects of iPod technology."
On the other side, Peter Cho, who works closely with Vlado Meller, one of Universal's top engineers, defended tasteful compression. Meller has mastered CDs for a wide range of artists, such as singers Celine Dion and Julio Iglesias and metal bands Metallica and Slayer. Many request some compression, Cho said, because it enhances their recordings.
He also noted that not all music is intended to be subtle. "It's not always about dynamic range," he said. "There is also the hard rock effect and a pounding approach."
Still, he acknowledged, "People are pushing it beyond what might be tasteful at times."
Charles Dye, who has mixed records for Bon Jovi, Ricky Martin and Sammy Hagar, said many artists would rather have a full range of sound but worry that consumers will turn up their noses if the overall loudness seems too low.
"You wouldn't want fans who buy the record to think there was something wrong with the CD," he said, "when really all they need to do is grab the volume knob and turn it up."
With that in mind, Dye teamed up with other sound engineers to form Turn Me Up!
The nonprofit organization encourages full dynamic range on recordings. It hopes to certify music with stickers that read, "To preserve the excitement, emotion and dynamics of the original performances this record is intentionally quieter than some. For full enjoyment, simply Turn Me Up!"
"We're not criticizing people who use compression," he said. "We're simply trying to give artists back the choice to make more dynamic records."
Producers are most likely to use aggressive dynamic range compression on hard rock, hip-hop and dance music. The Seldon Plan's Nestor said it's becoming more common in independent rock, too, but "indie labels tend to be hush-hush about it."
"We walked into the mastering studio," Nestor added, "and the engineer said, `Look - if you want your CD played on the radio and TV, it has to be at this certain level.'"
Nestor said the compression was moderate but still noticeable. "Whenever the snare drum is hit," he said, "I can hear how much louder it is than when we normally record it or when we play live."
The concession might have paid off. Nestor said MTV has expressed interest in making tracks from the new CD into background music for a show.