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Comment by laughing_man | Hacker News Reader

Broadcasters used to say the ads were no louder than the regular programming, but the "density" was higher, so the seem louder, and that if you measured them with a dB meter you wouldn't see any change.

That was years ago, though. I wonder if it was true back then, and if so whether or not it changed over time.

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It was only ever true by an extremely specific, now outdated, definition of loudness. Basically commercials back then would have the audio extremely compressed, such that they were always at the maximum possible volume allowable by your system at a given volume setting, whereas content mixed to be enjoyed would be mixed such that there are louder and quieter moments, which is both gentler on the ear and more dynamic.

You know how movies are mixed such that they have really quiet dialogue and big explosions are like 4-5x as loud? Commercials are in explosion-mode the whole time.

So yeah, commercials are mixed louder than the rest of the content on purpose, just to try to snag your attention. If they could, advertisers would come into your house and turn the volume on your AV receiver/soundbar/tv/computer/phone way up themselves.

Music albums have been suffering by dynamic range compression as well. They apparently sell better since they sound louder, but information is lost in the process.

https://en.wikipedia.org/wiki/Loudness_war

As I understand it radio stations used to like "loud" albums because people can't hear the quiet parts in their car as a result of road and engine noise. And people bought what they heard on the radio, generally.

I'm not sure that's still true. Music fans seem to be pretty heavily siloed, so they're probably discovering music through the internet somehow and not radio.

That's the leading theory for why CDs started to get compressed. It happened right after portable and car CD players hit the scene in the early nineties.

This has mostly ended in most genres of music due to audio volume normalization algorithms in streaming platforms like Spotify and Tidal.

right now there's an industry standard way to measure perceived loudness, and at least in saner places - the limits were already set in place.

> density

It’s reduced dynamic range, this is done using audio compression which, roughly, has the effect of making the quiet parts louder and and loud parts quieter, then the volume level can be increased. The overall effect is to keep the decibel levels the same, but the every sound within the range is now shouting at you.

> has the effect of making the quiet parts louder and and loud parts quieter

Not quite. The ceiling of the signal is the same. The quiet parts have gain added but the louder parts (over the threshold/above the knee) receive no modification at all.

Once compression is complete you might even do a normalization pass to ensure that the loudest impulse in your audio achieves 0dBFS.

Put the two together and you have a "wall of noise" effect.

I wrote “roughly” on purpose, but I think your description is wrong. A compressor triggers when the signal goes above a threshold, this applies a compression factor to the loud signal, which reduces the overall gain of the loud sounds (they become quieter). That is what reduces the overall dynamic range. Making the loud sounds quieter.

Most compressors then have a ‘make up’ gain control to recover the lost volume. That process makes the quieter sounds louder.

Your description sounds like an expander.

I think what they meant by "density" was that the entire commercial was near the max volume, whereas the show you were watching was mostly at a lower volume with occasional peaks.

You're literally describing dynamic range. The volume is the same in the show and the advert, but the perception of loudness is completely different. You perceive the adverts as louder because of the reduced dynamic range, even though they're not actually louder at all. This reduction in dynamic range is done by pre-processing the audio [in the advert] with a compressor. It lifts the quieter sounds (reducing the dynamic range), which creates more of a 'wall of sound' but the overall decibel levels are the same.

https://www.uaudio.com/blogs/ua/audio-compression-basics

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