Tuesday, May 25, 2010

Frequency response of microphones now extends into UHF and beyond

Our notion of the audio passband being something like 20-20,000 isn't really accurate. Most people, even younger ones, have little to no hearing above 15K.  Yes, I know, YOU can hear something up there, or think you can. Actually just about everyone who visited the microphone lab in years past got a secret hearing test, and I found out that some very good ears could hear nothing above 10K, but that's another story.

Fast forward to the present, or near future, when everything is wireless - wireless is a quaint old term that was used from about 1920 to 1990 to describe ancient radios with sparks, code keys, and old men with beards. The term was "radio". The term "wireless" has had a revival and now is part of the every day lexicon.  Wireless everything means lots of traffic on the airwaves, which are finite, and crowding, interference, and noise.  Eventually, the so-called recording studio will be wireless, or, possibly, wires will make a comeback, like vinyl.

Wireless performance has become the norm.  You hardly ever see wires on stage any more, so ubiquitous are wireless body packs, mics and monitoring systems.  It's great for the performers and the audience, but also a challenge for the growing number of live audio companies who are charged with the now ever daunting task of interference-free music via radio waves.

Above you see a thing called a Spectrum Analyzer. This tool charts radiofrequency energy, including that kind of "RF" that goes out over the air, and into a sound system.  It has become a necessary tool for those who must arrive, set up, and operate complex wireless audio systems in various venues.

If you look closely, you will see the familiar spectrum displayed from left to right, lower frequencies, just like in audio, at the left, and going higher. Except, these are ultra high frequencies in the 800 MHz range, in this picture, which are used by cellphones. Soon cellphones will be in the "microphone" bands in between TV stations. It's a mess and manufacturers are worried that their customers are going to get interference from new cellular and other wireless services that compete for the precious, limited, and finite radio spectrum.

All wireless systems depend upon the use of at least one antenna. Antennas are a type of sensor, and the way an antenna behaves can be tailored to favor a specific job, frequency, location, or battle competing RF signals, thereby reducing interference.

The antenna art is mostly old, with a lot of old notions, myths, and obsolete practices. Those of you who followed the development of Crowley and Tripp Microphones might guess what comes next.

Here is a link to a java applet spectrum analyzer you can play with.

3 comments:

David said...

"Eventually, the so-called recording studio will be wireless, or, possibly, wires will make a comeback, like vinyl."
So it's just acoustics not wires that make studio recordings better than live recordings?

David said...

"I found out that some very good ears could hear nothing above 10K, but that's another story."
No surprise here! HF has been overrated for years. Instruments & voices live in the LF.

Bob Crowley said...

"Better" is subjective, of course. But no, it's more than acoustics, there are a lot of things that make a studio a well-controlled, productive and high performance place to produce music. And today, there are plenty of wires. That's fine, as wires are a lot simpler and what people use - for now at least. Years from now - who knows how many - things could be different.