How to Mix Sound, Session 3: What is feedback?

Feedback happens when sounds are reinforced without being limited. Any space will absorb and reflect sound in its own unique way. It’s when a microphone, amplifier, and speaker are added to the space that the fun begins. There is a range of the sounds that are absorbed into the space or reflected harmlessly into that same space – we don’t generally care about those so much.

But the sound frequencies that are not reflected or absorbed – those are the ones that concern us. Those frequencies are said to ‘stand’ in the space, hence the term ‘standing wave’. It’s when those standing frequencies are re-projected into the space that we get feedback. Those frequencies become reinforced, and then ‘feed back’ into our open microphones. After some practice, you can tell the frequencies that will cause feedback with your equipment, just by listening to the way the space wants to ‘ring.’ when you project sound into it.

We did this earlier by clapping, talking, and … listening.

The way a space ‘rings’ or feeds back into the equipment is affected by several different things:

  • Temperature and humidity
  • Number of people in the space
  • Placement of microphones
  • Placement of speakers.



(It’s the same. We’ll continue to do this to help you condition your ears to spaces and how they’re created in the final mixdown.)

Find yourself a copy of some ‘classic’ music and listen to how the sound crew put together the three-dimensional stage of sound. Find something that matches your tastes and give it a good, deep listen with your eyes closed. Some examples would be:

  • Classical and symphonic music from most any era
  • Jazz music from any era up to the 80’s
  • Rock/Pop from any era up to the 80’s
  • Vocals from any era up to the 80’s

So why not later than the 80’s? There was a big breakthrough in recording technology (the dbx Compressor) which took a lot of the creative burdens off the sound crew. Or they just got lazy because ‘the compressor will catch it’. Concurrent with that, recording profits began to fall dramatically. People began to get lazy about how they did mixdowns in the effort to get the music out and to bring dollars in. The early CD compression technology also required a lot of extra effort to get the mixdown right, and producers just didn’t have the time/money to spend on the art and craft of a really good mix. Of course, painting with a broad brush never works; there are performers like Barbra Streisand (for instance, and of course there are many others) who cared a LOT about every single aspect of the end product, and it shows. Other examples are Jefferson Airplane, the Bee Gees, Bob James, It’s A Beautiful Day, and individual performers like Liz Story.


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