Why are advertisements louder?

[Seeuzin]

Ooh a sound thread!

TL;DR version: It probably to do with the compression.

Long version: Let me give an example. MP3 format sound is a sound-compression format which removes all frequencies which are inaudible to human ears, as well as many frequencies which are audible but on the "fringe" of human hearing. .WAV, on the other hand, retains almost all frequencies that were present in the original recording of the sound.

You might not think it, but when paying attention, this actually has quite a noticeable effect. If you take a song that was originally recorded to .wav format, and convert it to an .mp3, many people will report that while the volume of the song is the same (and is discernable as such by looking at a volume meter,) the mp3 sounds less "rich." I can hear this difference when I convert .wavs of songs I like to MP3, and would describe it as the sound being less "in-your-face." The notes played are the same, but since the very lowest and highest frequencies are cut out, the sound sounds a lot less full. It's a hard quality to describe.

"Wait, how can you remove frequencies from a song without changing the pitch of the notes? Doesn't pitch depend on frequency?" Surprisingly, not entirely. If you want to see for yourself, download Buzz (www.jeskola.net) and play with the lowpass and highpass filters. Lowpass will filter out high frequencies and allow smoother-sounding parts of the sound to pass through, whereas a highpass filter only allows higher frequencies, producing a more grating kind of noise. This is part of why two bass synthesizers can play the same note, an A sharp, for example....yet one can sound smooth, and another can sound grating, gritty, and edgy. It's the exact same note, but with different filtering effects, different frequencies will come through more prominently, and this changes the quality of the sound (without changing the note played.) These kind of filtering effects are used often in dubstep to "mangle" the bass notes and get them to sound they way they do. (I may dislike Skrillex, but he's kind of a genius at filtering.)

So to my point...changing the frequencies present in a recording changes the way it sounds to the human ear, whether radically (aggressive filtering) or subtly (compression.) It's entirely possible the audio is less compressed in the advertisements by design. Lack of compression gives the sound a more "in-your-face" quality (which is what advertisers want)...without changing the volume on a measuring device! Sneaky. And I wouldn't have believed it had I not played with this stuff and heard it for myself. Hope this helps.