The HAMMOND ORGAN

North Suburban HAMMOND ORGAN Society

Figure 4. Typical Hammond tone wheel generating the AC signal for one note or pitch of the musical scale. The electrical output signal is represented by the sinewave at the upper right.

Figure 4. Typical Hammond tone wheel generating the AC signal for one note or pitch of the musical scale. The electrical output signal is represented by the sinewave at the upper right.

This diagram, as well as those on the next two pages are conceptual diagrams, in that they illustrate a concept but are not truly literal representations of what really happens. In this first diagram, we show a sine wave signal entering what is known as a circular buffer, essentially a memory which holds a certain amount of digital information. As more is added, the earliest info gets removed. At the same time, an output, represented by the square at the top of the line takes the signal out of the buffer which is indicated by the words, "signal out" and another sinewave. Notice that both sine waves, the input and output, have exactly the same frequency.

Digital pitch shift can be very subtle with a change of only a few cents. As such it can be used to add a "celeste" effect or otherwise destroy the precise tuning of some electronic organs. In other cases it may also be subtle but vary at approximately 6 times per second both slightly above and below the input frequency. This will produce vibrato. In still other cases, it may change the pitch a lot more, such as a whole tone, several whole tones, or even an entire octave.

Please note that this is a Flash movie and Flash content will not display adequately on some cellphones. Please view this on a computer or laptop where you can see this, and the corresponding images on the next two pages in actual motion, as that will graphically represent the concept of changing the pitch of an electrical signal.

 

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