Feed back is a term that musicians who use amplification, like myself, are very familiar with. For those who might not be used to the phenomena, an audio feed back can be quite annoying, in particular for singers who walk around concert stages with a microphone. When a mic gets too close to a speaker, it picks up the resonant frequency of the room and sends it to the speaker after being amplified by the P.A. system. This is then picked up by the mic again which sends it a second time (feeding it back) through the system around the same loop. Soon enough it amplifies itself out of control and produces a loud whistling sound. By moving the mics away from the speaker you break the loop.

On the other hand musicians, in particular electric guitarists, have learned to use this to their advantage, and have created a unique blend of guitar tones and controlled feed back into the rich sustained sound that is so unique to the instrument. One example would be the tone of Carlos Santana’s guitar.

So there is two sides to the feed back loop- the Dr. Jekyll and the Mr. Hyde.

There are many examples of feed-back loops, and one of them has to do with bridges, which I’ll get to in a minute, but in thinking about this it came to me that this could also explain another musical phenomena. I am thinking of the one we call “groove”. As a percussionist I am always concerned about it; is it good, or is it not good? What makes it good, or what makes it lame? What is a groove, anyway? I’ve never seen a definition of it; the only thing I know about it is if it is there or not. I then read this story about the London Millennium walking bridge and as an analogy it made perfect sense…..

The closest thing to a string in the everyday world in which we live is the bridge; it is long, stretched, and subjected to all kinds of vibrations.

When the London Millennium bridge was open to the public, people enthusiastically started to walk on it in great numbers, but it wobbled a little bit, which then fed back to the people, which made them want to synchronize their footsteps to the bridge’s motion, which made the bridge’s motion worse. In other words, the situation created a feed back loop between the bridge and the foot steps of the people. It is not a new phenomena, it has been well known for a long time; military parades have to break their lock step while walking on a bridge, because they could create such a feed back loop that they could collapse it.

So, to me, a groove does behave in a similar way. There is no physical bridge or amplification system as previously, but only the sympathetic relationship between the different elements that constitute it. They re-enforce each other by feeding back in a looped pattern. The common denominator is the down beat, which can be present or only suggested by the interlocking parts. A groove is made of at least two parts (bridge-steps or mic-speaker), or, in this case, down beat and syncopation. But it can include many different parts.

When a groove is locked in, and it is important to stress that this word is a paraphrase helping us describe the “groove” phenomena the best we can (there is no lock on a groove), in this case the analogy is the lock step of the aforementioned parade. When a groove is locked, it means that the feed-back loop is enabled and is re-enforcing each part in relation to the other. To make another ‘bridge’ to the scientific lingo, you can say that the synergy is at its highest, the whole become larger than the sums of its parts.

Just listen to African, Latin American, Jazz and Funk music, and when the feed – back loop is enabled, feel your step locking with the groove, and as with the Millennium Bridge– shake your whole body.