Home on the Ranges

By Jay Rose Courtesy of DV.com

Audio manufacturers have started a buzz about 192 kHz sample rates, which theoretically pass signals up to 96 kHz-a couple of octaves above what’s normally considered the top of human hearing. This may be fine if you’re recording hymns for hummingbirds, but tossing all these high-frequency numbers around has fooled some filmmakers into thinking sounds are higher-pitched than they really are. And that can lead to bad decisions when choosing equipment or equalizer settings that hurt a track more than help. Fortunately, you don’t need golden ears to understand which frequency ranges are important. In fact, you hardly need ears at all-just your eyes and brain, and a few screenshots.

But first, you’ll need to understand a tiny bit of math. 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 a few hertz can sound the same as 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 difference. That same interval at the top of the keyboard has a difference of more than 500 Hz. Our hearing extends between roughly 20 Hz and 20 kHz, which 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. What’s 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

For the screenshots, I cut together some soundtrack elements: female and male announcers, synthesized and orchestral library music, and female and male pop singers with their groups. I made copies and filtered them so that each carried only a narrow band of sound. You can download audio clips of the results at my Web site, www.dplay.com/dv. Listen with good headphones and you’ll learn a lot. But even without listening, you can start to understand frequency bands by using a spectral analysis program such as SpectraFoo (www.mhlabs.com). SpectraFoo graphs volume at different frequencies over time, allowing you to see exactly what’s going on in each band for each of my example tracks’ sources. The results will probably surprise you. If not, at least the graphs are pretty.

Figure 1 is the extreme bass, between 10 Hz and 100 Hz. I’ve added callouts so you can see how SpectraFoo displays an ongoing sound: time marches from left to right, frequency ranges from bottom to top, and power is displayed as changing colors. The labels on top identify the sources. Most of this bottom band is filtered out during dialog recording, to avoid noise. But it hardly matters. As you can see, none of the female voice and only a tiny bit of the male extends that low. What’s also interesting is that very little of the scoring music-well-recorded library cues with no additional filtering-goes below 60 Hz.

Figure 2 shows the mid-level bass, 100 Hz-300 Hz (there’s activity above 300 Hz because even my lab filters aren’t perfect). Now the voices start to come alive. These are the fundamental frequencies for most vowels. But you can’t tell male from female here; that happens at higher harmonics. The music uses these frequencies primarily for accompaniment.

Figure 3 is the low midrange, 300 Hz-600 Hz. These are the lower harmonics of voice frequencies, formed by resonances in the mouth. This is also the first band in which you can discern individual vowels, which you can see gliding as the speakers vary their intonation. This band is critical to mixing because it contains most of the energy of both voices and melodic instruments. These elements have a real potential to compete here, which is why alternate versions of scoring music-without melody lines-are often easier to mix. For the same reason, jingles and other music in which the lyrics are important usually don’t have melodies under the singing.

Figure 4 is the midrange, 600 Hz-1.2 kHz. Note how the female voice, naturally brighter, is stronger in this band. But these frequencies aren’t particularly critical for dialog, and you can mix music hotter here. Note how musical activity seems more organized in this image than in the previous ones: This band contains the harmonics that let you tell one instrument from another.

Figure 5 is the high midrange, 1.2 kHz-2.4 kHz, an important band for dialog. There’s enough harmonic energy to tell most vowels apart, and all of the consonants start around here. Our example singers are particularly strong in this range because they’re trained to sing in the mask, opening resonances in their face to emphasize harmonics. But despite the activity in this range, volumes aren’t as loud as they were an octave below.

By the time you get to the low highs, 2.4 kHz-4.8 kHz (see Figure 6), volumes are definitely falling off. While most vowels have harmonics up here, they’re not important for intelligibility and merely establish presence. (Telephones cut off at 3.5 kHz, yet retain enough of a voice that you can identify who’s speaking.) This band is critical for the brass instruments in the orchestra, which are rich in upper harmonics.

The octave above, 4.8 kHz-9.6 kHz (see Figure 7), is mostly sizzle. You can hear just a little of the female voice and only the friction consonants from the male voice. The synthesized music is almost completely gone. There’s still some strength in the pop pieces, primarily upper harmonics of the strings, the lead guitar, and the percussion. This band is important for adding life and brightness-that’s why most radio music is mixed to emphasize it-but doesn’t convey information.

In Figure 8, the top octave of the audio band (9.6 kHz-20 kHz), there’s hardly anything going on with dialog (remember, the green areas are so soft they’re almost inaudible). Only the orchestral brass and artificial harmonics added to the pop have any energy. If you listened to this track by itself, you’d have absolutely no idea what was going on. The presence of these frequencies may help things sound more live than canned, but NTSC television and FM radio are limited to 15 kHz, and most people are satisfied with this sound. In fact, it takes really good ears to even hear the top of this band.

What it all means

I chose most of these bands to be an octave wide, so each would contain the same number of musical notes. (The two lowest bands are considerably wider because hearing is less acute down there.) But the frequencies aren’t magic. I chose them to reveal interesting things about voice and music, not because you necessarily should be equalizing at them. However, you can make some general conclusions.

Don’t worry about dialog below 80 Hz. Attempting to boost down here will just make things muddy. Leave this band for music and sound effects.

Feel free to boost music a couple of decibels somewhere around 800 Hz, using a broad curve.

Watch out for music interfering with dialog between 1.5 kHz and 3.5 kHz. This is where the consonants live. Dipping the music a few decibels in this range can make the mix sound smoother.

If you’re boosting above 14 kHz or so to make a track brighter, you’re probably just adding noise. Try the same thing between 7 kHz and 10 kHz for better results. And for heaven’s sake, don’t obsess about 96 kHz or 192 kHz recording in a film. While working up there does present some advantages for critical productions, it’s more important to get the area below 10 kHz sounding right.

Rights redux

Last August’s column on music copyrights (Audio Solutions: “Copy Rites,” Aug. ‘03) generated quite a bit of mail for me and Kevin Koloff, the entertainment attorney who provided the article’s legal expertise. Most was complimentary, but there was also a complaint. “The article was okay as far as it went,” a reader wrote, “and I’d like to obey the law, but there was nothing about whether a small film company can even get the right permissions, let alone how.”

So I went ahead and asked another expert, Cheryl Cooper. Her company, First Light (www.firstlightclearance.com), specializes in securing music clearances for corporate and independent producers. From Cooper’s point of view, securing some kind of usage rights isn’t difficult. “Ninety percent of the time, we find a solution,” she assures. “It’s surprisingly rare to hear ‘No, you can’t use that,’ though there are some artists you know to stay away from, and others who expect Nike-sized payments. And even in those cases, if the producer is flexible, we can almost always clear something similar.”

Budgets don’t have to reach the Nike stratosphere. Cooper has gotten rights to use Bob Dylan’s music in a corporate meeting video for $1500, and U2’s in a hospital fundraiser for much less. “The problem is that there are no set rules. Nonprofits can be easy, but corporate productions may be more expensive or even impossible, if the artist doesn’t want to seem to be endorsing the company. On the other hand, independent features can be surprisingly cheap. You can get a license for between zero and $500 from almost any artist, giving you the right to use their song for a year at film festivals. They want your film to be a success, and for you to become the next Stephen Spielberg. The giant record companies are actually trying-in their own way-to help young filmmakers. They figure you’ll be good for much bigger dollars if the film is released to theaters.”

It all comes down to your negotiating skill, luck at finding the right people, persistence, and understanding of the realities of the business. That’s where a professional such as Cooper and her well-stocked Rolodex can be handy, and many filmmakers find the few hundred dollars she charges per song to be a good investment. First Light’s email is cheryl@firstlightclearance.com.

Speaking of realities, the amounts above are just for the sync license. Master and repro rights are extra, unless you produce your own version of the song. If that’s confusing, re-read Audio Solutions, “Copy Rites.” And of course, even $500 may be unrealistic for some projects. The article also has some strategies for the wedding and noncommercial-event videographer.

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