B3 Harmonics question

[Phred]

I am having a hard time convincing myself that a B3 works the way that I know it works.

 

I am familiar with the idea of harmonics, but whenever I think that the sound produced by something like 888800000 is 4 sine waves, I constantly wonder why it doesn't sound like a chord.

 

I will try this experiment at home tonight. If I pull out the fundamental (008000000) and play this chord:

 

C2 C3 G3 C4

 

will it sound like a single note played on C3 with a register of 888800000?

 

I find it hard to believe, but think that is what should happen right?

[mate stubb]

More or less - your basic idea is sound. In both cases, you are activating the same 4 tonewheels. However, there is some loudness tapering going on via resistive wire in the key contact wiring loom. When you play a single note 888800000, some of the upper drawbars are be getting attenuated slightly. I would expect it to sound very close, but with the tone balances off somewhat. It will sound less like a chord when the upper harmonics are knocked down slightly softer, thus emphasizing the fundamental 8' and 16' pitches.

 

If you have a 2 manual organ, try 888800000 on one manual and 008000000 on the other. Then mute the lower drawbars on the first manual: 000800000. Find the corresponding pitch on the other manual using the 008000000 setting and alternate playing them. I'll bet that the note from the 008000000 setting is louder.

 

Just to confuse matters, another opposing effect is called loudness robbing. When you play full chords, the loudness gets squashed a little bit by the impedance interactions of the system. This is actually a good thing - it makes single note leads jump out a lot more.

 

Hope this helps!

[JMcS]

This site shows how the tonewheels work:

http://www.keyboardmuseum.org/v_teach/hamtone.html

 

(Place the mouse over the key)

 

This site shows how adding drawbars builds a sound wave:

 

http://theatreorgans.com/hammond/drawbar.htm

 

This one shows how the Leslie works it's magic:

 

http://www.keyboardmuseum.org/v_teach/lesliespeaker.html

[The Real MC]

The Hammond drawbar system is an additive synthesis system, AKA a fourier series generator. It has its limitations in fourier synthesis in that the harmonics are tempered and limited to nine total.

[JeffLearman]

First, your experiment should prove that you're correct: the two should sound almost identical. And in fact, the organ is tapping the same amounts from the same set of tonewheels.

 

The reason this confuses you is because, for most instruments, the following apply:

 

1) the fundamental is not where most of the volume is. It's generally in 1st and 2nd harmonics.

 

2) Adding two different notes with a complete set of harmonics for each is very different from adding two pure tones in the same harmonic series -- even when the notes are in the same harmonic series.

 

That second one is confusing, so let me explain that more clearly. Let's take an example of playing a note and its octave, on a typical instrument. Imagine watching the spectrum graph as we play the notes. When we play the first one, we see well-defined spikes for each member of its harmonic series (up to where the highs get rolled off). Note that the spikes get closer together as we go up the harmonic series: the biggest gap is between the fundamental and 1st harmonic. Now, we stop that and play the note an octave higher. We see almost the same pattern, but shifted right by an octave. Note that the pattern includes spikes where there weren't spikes for the first note, and has spikes where there weren't for the first note. In other words, the harmonic series for a harmonic does not fall int the harmonic series for the fundamental.

 

Thus, playing a chord consisting only of notes in the harmonic series, does not sound like a single note. This is the thing that you already knew instinctively and intuitively, and why you found your hypothesis hard to believe. But your hypothesis deals with an electronic instrument that's created by summing tonewheels with very limited harmonic series, rather than recreating true complete harmonic series. Your intuition was valid but just doesn't apply to this simplified situation.

 

BTW, the tonewheel on a hammond isn't a sine wave, not nearly. It was intended to imitate the pipe on a pipe organ. There were some early electronic organs that were designed using sine waves and harmonic series, but they sounded like dirt, IMHO. Not until the Fairlight did harmonic additive synthesis get sophisticated enough to be very musical. (IIRC, there was another additive synth about the same time as the Fairlight, but I don't remember the name or which was first.)

[The Real MC]

Originally posted by learjeff:

(IIRC, there was another additive synth about the same time as the Fairlight, but I don't remember the name or which was first.)

The 1979 Crumar GDS, later to become the DKI Synergy, preceded the Fairlight by a year.

[Bridog6996]

In a basic way, you're right, playing a single note on organ usualy results in a chord. That's one of the main reasons why you need to play thin chord voicings in order for it not to sound muddy.

 

Experiment with the drawbars while holding a single note, and you'll hear how the different tones get added and subtracted. You're probably not "hearing" the notes as chords because we're talking about octaves and fifths here. The only drawbar that controls a tone other than an octave or fifth is the 1 3/5' drawbar, which adds a third (technically, a 17th since it's two octaves up).