Advantages of this approach include cheapness and simplicity (though top octave generators are not as easy to obtain as they once were) and an organ which is always in tune, but there are a number of snags as well. Each semitone output is applied to a binary divider such as the seven stage CD4024 to provide the lower octaves. The former use a digital ‘top octave generator’ to produce the 12 semitones of the equal tempered scale, all the intervals being, if not exact, at least very close, and of course ‘set in concrete’. The main varieties are divider organs and free phase organs. One of these applications is as tone sources in an electronic organ, or rather in one class of electronic organs, for there are a number of distinct approaches to design of these, each with its own advantages and disadvantages. These are well illustrated by the subject of this article – keyed tone generators, such as might be used in the two-tone alarm generator of an HF radio telephone or a hundred other applications.

Practical analog circuit design is fraught with snags, compromises and difficulties at every turn. Ian Hickman, in Analog Circuits Cookbook (Second Edition), 1999 Introduction

Multisim 12 ac sweep