How can I apply Dynamic Range Compression to my iTunes library?

September 2, 2008 1:43 PM

How can I apply Dynamic Range Compression to my iTunes library?

We all know, of course, that Dynamic Range is usually a good thing. But when I listen to music in the car, much of my music has me cranking the volume up and down all the time to hear the quiet bits, and then avoid being deafened by the loud bits.

I have too much dynamic range.

What I want to do it make separate versions of some of my music which have had their range reduced so I don't have to drive with one hand on the volume control.

I'm on a Mac, and am aware that I can do this using Audacity (the "Compressor" effect) but it's a pain to have to rip to WAV, compress using Audacity, then convert to AAC or MP3 (and manually type in all the lost metadata).

What I really want to be able to do is to automate this during the ripping process, or, alternatively, find an easy way to compress existing MP3s or AACs without wiping out the metadata.

Any ideas?

posted by Mwongozi to technology (10 comments total)

Isn't this what the "Sound Check" feature in iTunes and iPods (under Settings) is supposed to do? See Apple's Sound Check doc for more details. I'm not entirely sure if that only handles volume differences between songs, or within songs as well.
posted by zachlipton at 1:52 PM on September 2, 2008

Sound Check just applies a single volume adjustment to the entire track, which isn't the same thing. DRC "adjusts the volume" (a simplistic description, but it will do) continuously during the track, making the loud bits quieter and the quiet bits louder.
posted by Mwongozi at 1:54 PM on September 2, 2008

Sorry, I now see that Sound Check works on a track-by-track basis only.

Since this is for your car, you could consider using a small hardware compressor/limiter between your music player and the car stereo. Something like this PreSonus (only has presets, no manual control of the compression ratio) or this Samson would fit the bill. I haven't used either so I can't speak for their sound quality.

If you're on Windows, a google search for "batch mp3 compressor limiter" gave me Graphic Equalizer Studio along with a bunch of sketchy seeming links.
posted by zachlipton at 2:03 PM on September 2, 2008

Audacity has some scripting support but what youre probably looking for is one of these plugs-ins. Perhaps Batch-Chain.

Also, I would test this on 10 or so random songs. I find compressing music already mastered/compressed/massaged by the pros doesnt work out too well.
posted by damn dirty ape at 2:04 PM on September 2, 2008

You might be better off trying to level the perceived volume of your MP3s and AACs, not the dynamic range.

You can do something like this by using a program called MacMP3Gain. It changes the volume of songs to an ideal level, without having an effect on the quality. There are many audiophile programs that use the same method, it's called Replaygain.
posted by robofunk at 3:01 PM on September 2, 2008

Not sure if this is what you want but I have used IVolume successfully. Mac and Windows version.
posted by TheRaven at 4:05 PM on September 2, 2008

But MP3Gain just does the same thing as Sound Check - it adjusts the overall volume of a track, not moment-by-moment. iVolume looks to be the same thing.
posted by Mwongozi at 1:19 AM on September 3, 2008

Look for an MP3/AAC normalizer (the more common term for DRC). They are pretty common. You will have to maintain two music libraries if you care about quality at all.

Many new cars have a type of DRC built in these days, and will sometimes even increase the compression at higher speeds to compensate for road noise. Your car might already have this if it has a line-in port, different car companies call it different names. I think there are probably even aftermarket stereos that have the feature.
posted by robofunk at 7:47 AM on September 3, 2008

Normalization is not the same as DRC.
posted by Mwongozi at 8:55 AM on September 3, 2008

I wasn't going to mention it because it's Windows only (maybe you can use bootcamp or one of Windows Mac emulators or whatever), but the only program that I know can apply DSP effects while ripping a CDs or transcoding an audio files in batches is Foobar2000.

The DRC plugin for foobar2000 is Vlevel.
posted by robofunk at 8:16 AM on September 4, 2008