I’m working on a project for a local film composer. He has put together a bunch of 96 kHz/24-bit, 5.1 surround tunes in the “electronica” style (they include acoustic instruments as well). And they’re really good! They have the familiar pulse drum/percussive beats, lots of smooth filtering, and aggressive 5.1 surround panning. Not surprising considering this guy has spent his life in and around music, recording studios, and dubbing stages. His “garage” studio is one of the most incredible places I’ve ever been — and I’ve been to a lot of studios. He has a very large API analog mixing console (and a small one in the iso room), lots of signal processors, a huge patch bay, a 5.1 surround set of ATC speakers, a drum set, grand piano, guitars, and a bunch of microphones. And it’s all set up ready to record anything passing inspiration. When you’re responsible for 25 minutes of new music every week for a popular TV series, you develop a highly optimized workflow.
The API console is a monster. As you know, I’m a digital guy when it comes to large format recording consoles but I’ve worked on large analog mixing desks from SSL, Neve, Harrison, and Yamaha. The only other time that I’ve encountered an API desk was the custom one that my friend Peter Otto purchased for UC San Diego music department. My memory has faded somewhat when it comes to the API console that they ordered — and which was never completed — but I do remember that the university paid something like $600K for this fancy new state-of-the art mixing console and had to sue the owner of the company and API to get them to finish it. API has a reputation for excellent sounding analog consoles but they have flirted with disaster in their business dealings a number of times. But they’re still in business and still selling expensive consoles. People seem to like the sound.
So I get the first tunes from the composer and take a peak at the frequency response and dynamic contour in Adobe Audition. And there is — a huge red horizontal red line hovering in ultrasonic space above the rest of the music. This is definitely not part of the music. Any harmonic components are always down -80 to -100 dB at 40 kHz. The 40 kHz tone represented by the red line was only -40 to -50 dB down. Amazing! I immediately called my collaborator and asked him about it. I wanted to know if he has used some fancy signal processor or plug in that might account for the intrusive tone. He didn’t know where the spurious tone had come from.
So is the 40 kHz tone a problem or not? Obviously, no one is going to “hear” it and only speakers equipped with super tweeters will try to reproduce it. So what’s the problem? The signal path from source to speaker includes a lot of components that won’t want — and might have a problem with — a -40 dB ultrasonic 40 kHz tone! It’s possible to damage electronics with signals that are outside of their normal operating parameters. You wouldn’t plug 220 volts into a device expecting only 120 volts. And any thinking audio engineer wouldn’t record or mix to DSD 64 because it also has obnoxious amounts of unwanted ultrasonic frequencies that have been conveniently shifted above the audio band.
The mystery was solved when JMK called API and asked them about the 40 kHz signal. “Oh, sure,” they replied, “the automation system has been generating the 40 kHz tone for years but we fixed it some time ago.” No they didn’t — at least on this particular console. It makes me wonder how many so-called “high-resolution” capable consoles or devices have similar problems.
So I’ll remaster the tracks for this project and remove or attenuate the 40 kHz tones. But I shouldn’t have to do.