From hammond321@yahoo.com Thu Dec 13 07:08:53 2012
Subject:Re: Harmonic Beating ...What is It?
I thought my explanation with the airplane/boat motors was pretty good and simple... I guess it wasn't complicated or long-winded enough :)
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From: Bdec
To: "CloneWheel@yahoogroups.com"
Sent: Thursday, December 13, 2012 9:00 AM
Subject: Re: [CWSG] Re: Harmonic Beating ...What is It?
...but why do some Clones seem to emphasize the beating more than others? It is hardly detectable on my Roland VK7 and way too much there on my Casio WK-7500 db organ.
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From: "ccmacdon@rogers.com"
To: "CloneWheel@yahoogroups.com"
Sent: Thursday, December 13, 2012 8:46 AM
Subject: [CWSG] Re: Harmonic Beating ...What is It?
To explain Harmonic beating I go back to my highschool physics class where we learned about wave vs particle theories in physics.. I barely paid attention, and luckily managed to pass... and I think it's been replaced by string theory so... its all worthless info now.. ;-) For the record, I have no real technical background here but I have a simplistic way of looking at all of this, and I think it's relatively easy to explain.
If you think of a pebble dropping into a pond, it creates ripples of waves that travel outwards in a perfect circle. If you think of a pebble dropping into your kitchen sink full of water you see the same thing, but what you also see will be the wave(s) reflecting back inwards after the wave bounces off the sides of the sink.. As these waves bounce back, they will intersect each other, and it's when waves intersect each other that interesting things happen.. Where the high point of two waves intersect you get a higher wave (the sum of the two waves), and the reverse is true where the low points meet. When you get the high point of one wave meeting the low point of another, the waves cancel each other out. That said, sound is not like a single pebble, it is a constant stream of waves at different frequencies, that constantly interact with each other sometimes on purpose, sometimes accidentally. The Hammond organ is actually an example of purposeful
interaction of waves, because it is based on the concept of additive synthesis, where adding multiple sign waves on top of each other creates a more complex wave.
When you have a Hammond clone that creates tones of very specific digitally perfect frequencies, and to that you add Chorus/Vibrato which modifies these tones in a rhythmic and extremely regular frequency, and then you put these modified tones through a digital leslie simulation that adds a further rhythmic effect (including changing pitch to simulate the doppler effect of the leslie speaker).. What you will find, is that secondary waves can be created, waves that resonate in a rhythmic manner.. This is what is being referred to as Harmonic Beating, when the sum of these waves, acting upon each, creates a secondary audible wave... it could appear like a phaser effect, or a rhythmic pulsing etc.
Waves acting upon each other can create resonance (basically an increase in amplitude/volume) when the peaks of two waves meet each other in a regular manner, and secondary waves can be created,. Some secondary waves are intentional, like the additive synthesis of the Hammond organ, and some are unintentional, like our harmonic beating. You can also create standing waves, and other wave phenomena. The out of phase effect is a little bit different in that it is about two waves cancelling each other out. If you take two identical waves, and you reverse the phase of one signal, and apply it to the other, the waves will completely cancel each other out (while one wave goes up the other is coming down = cancellation, no sound). This is most notable with lower frequencies, so often you'll hear/see an engineer checking the phase on a bass track recorded with multiple mics or inputs.. (it's possible that due to mic placement, two mics can record a track
completely out of phase,where one mic is placed at a distance where it receives the high phase of the wave and the other being at a distance where it is receiving the low phase of the wave). This is also the same effect that is used to cancel out vocal tracks which are almost always in the centre of the stereo field.. by reversing the phase of one side or the other you cancel out any sounds that are that are panned to the centre of the track.
I hope if any audio experts read this they don't say "Craig you're completely wrong", and sorry for boring those of you who are familiar with all of this, and understand harmonic beating. I just thought a clearer explanation was required, hopefully this will help.
BTW, you tend to see this more in digital clones because of the digital precision of the waves that are created (digitally precise tones, into digitally precise C/V, into a digital leslie sim).. This is my opinion of course, based on no real science beyond common sense. Real Hammond/leslies have no such digital precision, because of all the mechanical variables.. such as drag, friction, and slop in motors, gears, leslie pulleys etc. So these secondary waves have a difficult time getting established. There is no digital precision in a real Hammond/Leslie. Even the basic hammond tones are not pure/perfect. That said you can still find it if you look hard enough, there will be places in a room where you might be able to hear harmonic beating on a real hammond but that is probably more a sound reflecting off the walls, rather than the sound coming from the Hammond itself. Harmonic Beating is more prevalent on a clone because of the digital
precision with which it creates waves and the digital precision with which the effects (c/v/leslie sim) act on those waves.
I hope this explanation is helpful for those of you trying to understand "harmonic Beating" and also hope it's correct... ;-)
Craig MacDonald
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