31-Band Audio Processing Explained

31-Band Audio Processing Explained

31 BANDWe're asked periodically why we do the things we do. We don't have an answer for everything, but we have a few good ones for the features we've designed into our AirAura and FM-531HD audio processors.

Take our Bass Tools. This is for those of you who love to crank up the bass EQ in the on-air processor. Hence, the reason for the Bass Tools feature in our audio processors, which allows you to crank up the bass EQ without it affecting the dynamics of the other material. With Bass Tools, customized bass effects are added back into the final processing, creating a much more consistent bass sound without knocking the basement out of it.

Then there's our very clever AGC scheme with Density Compensation™, which allows you to squeeze every ounce of quality and loudness out of your programming with barely a flicker from the limiting section. We call this our Sweet Spot Technology™ and whatever overshoots do make it into limiting can be attenuated precisely using our 31-band limiter approach.

Which brings us to the 31-band question we know you're dying to ask.

We chose to design a 31-band limiter for our AirAura and FM-531HD audio processors because the center frequencies of the bands line up with the industry standard ISO 1/3 octave frequencies, which, as recording engineers/producers and audio professionals know, gives the most accurate model of how our human hearing works.

Anything less than 31 bands would be like trying to write without being able to use all 26 letters of the English alphabet. It would be kind of like text messaging in shorthand - you can get the idea across but it loses all nuance. Anything more than 31 would be like adding an extra letter. How awkward would that be?

Audio processors with fewer limiter bands aren't much better. You put in Herb Alpert's "Rise" and out comes something that sounds a lot like Lady Gaga. We're exaggerating here but the point is, your processor should be able to limit with a scalpel, not an axe, and not remix everything so it sounds like something else entirely.

Essentially, we upped the number of bands to keep overshoots in check without affecting a large number of surrounding frequencies. The idea behind our 31-band limiter is to do limiting as selectively as possible to protect the sonic integrity of your program material. Wheatstone engineers explain that because there's natural leakage from each band into adjacent bands, a typical four-band limiter will apply limiting arbitrarily across the entire 200Hz to 7kHz spectrum just to correct a little overshoot at 2kHz. That's a lot of extra and unnecessary frequencies being ducked out, and a lot of detail lost!

The bottom line is that the more limiter bands there are, the narrower those bands, and the more precisely you can limit just those frequencies that need it.

We know what you're going to say. What about all that band splitting? Doesn't that cause strange swishing artifacts? Actually, no. That might have been a problem back in the analog days of 1975, but today we have the mathematical precision and repeatability of DSP so we are able to do things that were once impossible and without creating the artifacts that plagued traditional band splitting methods.

See, we really do have an answer for everything.

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