By Noah | March 17, 2012
It’s that time of year again, and audio mastering engineer Ian Davis is reminding us to celebrate “Dynamic Range Day“. This is about improving the sound of the audio recordings that we buy on CD and stream through the Internet. Specifically, it’s about compression.
If you are into audio and recording you probably know why this matters. If not, here’s a quick tutorial: compression is a technique that’s used to reduce the difference between loud and soft passages in live or recorded music. Building a good sounding compressor is tricky, but the basic idea is to use a circuit or processing function that gently boosts the volume in quieter passages, but not in loud ones. (BTW: this is totally different from the file size compression that computer folks do — we’re talking here about audio compression). There are some good reasons for using compression, and some less good reasons.
The most obvious benefit of using compression is that it makes it somewhat easier to hear music or speech in noisy places such as in cars. AM radio, and the single records that were for years targeted at AM radio, were often compressed quite a bit. Even the quieter passages of these recordings could be heard well over the noise in a car. Gentle compression is also often used on the microphones of singers on stage; again, it helps the quieter passages to cut through, and it also helps compensate for bad microphone technique. Unfortunately, any processing of audio risks losing the impact of the original, and too much compression can kill any sense of space and dynamics.
Unfortunately, there’s another “benefit” of compression that has proven appealing for modern recordings: it can let you record at higher average levels. Any recording medium has some limit on the peak waveform it can convey. For digital, you get hard clipping if you exceed that level; for things like vinyl records, you get needles jumping out of grooves, distortion, etc. So, if you don’t use compression, and there’s even one loud drum hit or cymbal crash in your piece, you’ve got to turn down all the rest so that one bit doesn’t clip. With compression, you can bring up the rest, and that’s where the loudness wars come in. It’s not just that you can minimize the difference between soft and loud, you can actually make the recording much louder on average. If someone’s playing 3 songs in a row, and just one is heavily compressed and recorded “hot”, that one will tend to come blasting out louder than the others. In the interest of maximizing that impact, recording engineers have been using more and more compression in recent years. So, we’ve been getting a lot of crummy sounding recordings that are way over-compressed, recorded too loud, and that sound harsh and artificial. All the space and dynamics of the music is lost.
To fight back, Ian Davis is sponsoring the annual Dynamic Range Day, to encourage listeners to look for material that’s well recorded, and to encourage recording engineers to put more emphasis on the quality of the sound, and less on making it loud. Ian’s also written an Open Letter to the Music Industry.
Happy Dynamic Range Day.