How Compression and Normalization Affect the Listening Experience

One of my biggest complaints with CDs isn’t a fault in the media; it is the fault of the idiots who master them. It seems there is but one goal for them: to ruin my hearing. Great sound and great music require there to be several elements: punch, definition, and clarity.

Think of some of the most identifiable natural sounds. The crack of lightning followed by the roll of thunder, the spring peepers croaking in the woods, and the roar of the ocean; these sounds have a melodic quality, a rhythm and definition, and a definite change in decibels as the sounds are heard. Sounds that are considered pleasant most often mimic the qualities of these natural sounds.

There is a class of guys who lay down soundtracks for movies who understand this. Music becomes part of the experience: booming and fast paced in action scenes, soft and subtle during romantic scenes, and so on. This is demonstrated in movies like Lord Of The Rings and Legend where the music is blended in so well you almost don’t know it’s there. There are, of course, exceptions to this — movies like Mystic River where the music track completely drowns out the voice track at times.

Most music CDs don’t seem to get the kind of attention they should. Music CDs are compressed — a term that has nothing to do with the amount of size a file takes up, but rather the amount of range in the volume of a piece of content. By compressing audio, you never end up with sounds that are too quiet to be inaudible or so loud as to be deafening. Instead, you end up with audio that is very monotone.

This image shows four audio tracks. The first is an example of how audio should look, with a great deal of change in volume within the file: occasionally being truly silent, and occasionally being at its peak.

Next is an acceptable example. While peak isn’t reached at any point, there is a good amount of variation in the volume.

Sample three suffers from severe compression. This is a piece that no longer has any diversity — it is all monotone. This piece also never reaches a peak level, so to make the song soft, it was compressed but not normalized.

Sample four is very close to perfect. There’s good variation in volume, though it is normalized to a bit beyond peak (which can cause distortion).

In CDs you buy today, sample three is the most typical. The audio is compressed to the point where there is added distortion and all the “life” is gone. The music becomes severely ugly. This, of course, helps sell concert tickets because these days most everyone does sound better on stage. It also helps MTV as the unplugged music sounds much more lifelike than the music that gets passed off on CD.

Going back to the thunder example, below is a WAV of a thunder clap. The green is the WAV before audio compression, and the red is after. (I used Adobe Audition’s Radio Compression preset to ruin this beautiful sound.)


Compare the two mp3s. This demonstration is quite dramatic because the roll of the thunder (in the compressed example) doesn’t get softer the way it ought to. This isn’t to say that compression has no purpose. It is great for interviews and spoken word content where you want to keep mumbles audible and shouts to a small roar. But compression takes a lot of the emotion out of the sound. It’s like the difference between listening to NPR or listening to Martin Luther King, Jr.: an audio compressor makes everyone sound like Lynn Neary and Robert Siegel.

Because online music such as iTunes and Napster 2.0 use CDs as their source, the music I buy for my portable device sucks, too. Only it sucks more because instead of getting CD quality suck, I get near-CD quality suck. The distortion and loss of frequency response that results from a file being data compressed / encoded to 128 or even 192k stacks on top of the distortion added via audio compression.

Because each format encodes slightly differently, some content will sound better from one online provider than from another. AAC tends to handle content that is audio compressed better than WMA does, but WMA tends to handle the softer and more subtle sounds found in uncompressed audio. Because so much of what is sold online is pop music, this puts AAC in a better light than WMA in the format wars. If you are, however, interested in preserving your RCA Red Label 1812 Overture or you’re just transferring it to your portable media player, might I recommend WMA? You will find the cannons’ rumbles to be crisper and the subtle sounds of the children’s choir fading in and out to be much cleaner in WMA. Mp3 will lose some of the stereo separation that is much more important in orchestral music than it is in pop. If you look at the examples above you will notice that most of the music is practically monophonic; the audio in the left and right is almost identical, whereas the thunder is very different between channels. AAC has stereo separation equal to that of WMA but it tends to drop sounds below a certain db. Whether this was done as a noise reduction feature or if it is just a way to drop some of the bits that would never be heard by someone who has been to too many concerts, I don’t know.

I’m 32, so I don’t remember tube amps or 8 tracks, but I often think maybe it would be better to roll back to those days. When I bought my home theater, the salesman was trying to push me into a model that included 20+ surround modes from living room to concert hall to cave. Sure, that is cool for my Audigy card when I’m playing games and the programmers don’t have to presample all of those environments for each sound in the game, but like I would want to watch a movie in a cave, or hear Britney as though she were performing at the bottom of the Grand Canyon. (Okay, Britney and Paris Hilton in the bathroom surround mode crossed my mind briefly as I figured I could pretend they were naked in my shower… but that passed pretty quickly.) Perhaps I’m too much of a purist, or perhaps labels think their target audience is the guy with a 4000-watt, 42-inch subwoofer in his car. But for me, I’d like to hear the music the way you would in the studio — with all the subtlety and life still in it.

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  • Rob Sommerfeldt

    Don’t just blame the Mastering Engineers. Sometimes the Recording Engineers send their mixes for mastering already compressed, so there isn’t much they can do with those ones. Then there are the Producers and Artists who insist on having their songs AS LOUD as possible in the hopes that it will sound better to the average listener who is listening thru earbuds trying to drown out the real world. Unfortunately audiophiles are few and far between and while they spend large on gear, they don’t tend to buy much music as they are really picky about quality, so the market is not geared towards them. It would be nice to just tell everyone that there is a volume knob/button on their player, but that just doesn’t seem to make a difference.

  • Matt Hughes

    I was very happy when trent reznor was releasing flac copies of the ghosts albums

  • chris morrell

    absolutely and as this row demonstrated , “Hi Fi” is NOT the preserve of classical music geeks.

  • chris morrell

    absolutely and as this row demonstrated , “Hi Fi” is NOT the preserve of classical music geeks.

  • Paddy Gordon

    Compression makes sense for DJs at clubs etc to keep the volume solid during a song, there’s nothing worse than going from a loud song to a quiet intro and folk thinking the music’s been turned off. Then the main part coming in VERY LOUD and getting folk moaning that it’s too loud etc. or worse, it blowing your speakers/amp

    Makes some sense for people in busy cities etc with headphones, but iPods should have software compressors built in by now.

    The only place compression makes no sense whatsoever is in the home when there’s no external noise such as large crowds or diesel engines going by etc.

    I’ve routed my iTunes through logic’s compressor before when going to bed so the music stayed at a constant volume and I wasn’t woke up half an hour later with my playlist nearly finishing and a loud part coming on etc.

  • high_frontier

    Actually, I would not consider you a purist at all, as a real purist would not be listening to mp3s unless under duress of some kind.

    Part of the reason so much of music is compressed today is the poor equipment that many people have. To reproduce real music at realistic levels takes power, and lots of it. I does not matter what type of speaker we are talking about, lots of power is needed with even the most efficient corner loaded horns. [The problem with horns is that they introduce their own colorations and distortions due to their design.] The very best speakers are very inefficient and require levels of amplifier power most are not willing to purchase or live with.

    One anecdotal point that Bob Carver was said to make was how much power was needed to properly reproduce the shearing of a piece of paper with a scissors. At normal [same level as the real event] it took a couple of thousand watts to get the transient attack correct – this is why he was famous for high power amps throughout his career, like the Phase Linear 700 and various models that bore his own name.

    It is no wonder then, that for semi-realistic reproduction in the home, several hundred watts of clean power are needed, and we are not talking car stereo exaggerated wattage here. The amplifiers that reproduce this amount of power usually are 5 to 7 rack spaces in height, usually about 20″ in depth, and weigh in at at least 50 pounds. That is for a two channel amplifier. [ Don’t let anyone kid you, two channels of proper recording is all you need with the right equipment! ]

    I should also say that this amplifier is usually found at a price of over $1000, which is more than many people will ever spend on a sound system, thinking that the need is not there, or that differences cannot be resolved that make the investment worthwhile.

    That would be for each person to answer for himself, but if fidelity is desired, not only is compression to be avoided, so are sup-optimal digitization techniques, and low-fidelity playback equipment. [That would tend to be 95 – 97% of the equipment found in homes today.]