This is a shorter version of material from Jay's book Audio Postproduction for Digital Video (Focal Press, November 2002). A somewhat different version appeared in Digital Video Magazine, November 2003. Revised 2008.
by Jay Rose, CAS
THE AUDIO BAND is usually taken to mean "20 Hz - 20 kHz", meaning that humans can hear a range between twenty vibrations per second and twenty thousand. But to paraphrase Orwell, not all frequencies are created equal. Physics and human evolution dictate that the extremes of that range aren't very important. Even more interesting: what you might consider the entire top half of that range really doesn't have much going on!
This is vital to anyone working with sound, and particularly to those working with sound for film or video. Not understanding how this works can lead you to bad equipment decisions and bad mixes.
Fortunately, you don't need golden ears to understand which frequencies are important. Regular ears will do fine. But you'll also need your eyes and brain, and a few screenshots.
First, a tiny bit of math. Very tiny. If your eyes start to glaze, skip down to the next paragraph.
Frequency is measured in Hertz (Hz), the number of times per second a wave vibrates. Hearing is logarithmic: at low frequencies, a shift of only few Hertz can sound the same as a many hundreds of Hertz higher up. For example, C and D on the bottom of the piano are at 32.7 Hz and 36.7 Hz, just 4 Hz different. That same interval at the top of the keyboard is a difference of more than 500 Hz. That hearing range of "20 Hz - 20 kHz" might lead you to think the middle of the band — the dividing point between bass and treble — is around 10 kHz. But that's a very high pitch indeed, and only a few orchestral instruments even reach it. Actually the middle of the audio band is around 1 kHz.
The point of all this? Low frequencies pack more information per Hertz than higher ones, and the bottom 5 kHz of a soundtrack is more important than the 15 kHz above.
Battle of the bands
So let's get into it. I cut together some typical soundtrack elements: female and male announcers, synthesized and orchestral library music, and female and male pop singers with their groups. The montage sounds like this:
If you don't see a player below, you need the free QuickTime plug-in for Mac or Windows.
Producing Great Sound for Film and Video
published March 2008
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