Frequency Divider for Audio

Description

• Audio frequency dividers are digital circuits that count incoming electronic pulses. A divide-by-two counter, for example, produces one output pulse for every two input pulses. A digital wristwatch uses this principle, taking the precise signal from a 32,768 Hz quartz oscillator and sending it through a chain of divide-by-two counters from which it produces a 1 Hz pulse. Though a digital counter can take in a signal having any wave shape, it outputs only pulse waves. For a watch, this doesn̵7;t matter, though it imparts a buzzing quality to audio signals.

Ratios

• Simple digital circuits divide an audio frequency by whole numbers. A series of divide-by-two counters, for example, divides by two, four, eight or any whole power of two. Other circuits divide by other whole numbers, such as three, six or eleven. If you mix an audio signal with the output of a frequency divider, the divided signal tracks the audio signal̵7;s pitch perfectly, intensifying the bass registers of the sound.

Divide-by-N

• Most types of audio frequency dividers divide by a fixed number inherent in the circuit design. By interconnecting different counters, you obtain different frequency divisions. One design, called a divide-by-N counter, divides by any whole number up to a maximum determined by the circuit. By turning a control knob, you change the divisor. A musician can, for example, sweep the frequency division control up and down, producing a series of harmonic notes that follow the pitch of an audio signal.

Top Octave Synthesizer

• Many electronic organ designs use a set of digital frequency dividers to generate the twelve notes making up the top octave of the keyboard. The dividers use a quartz oscillator having a frequency between 1 and 2 MHz and divide it down to a few hundred Hz. The quartz oscillator ensures that the organ̵7;s pitch stays accurate. To obtain octaves lower than the top one, each note passes through a set of divide-by-two counters. As each lower octave represents a halving of frequency, the divide-by-two circuits fill out all the needed octaves. Electronics designers eventually incorporated all the digital counters for an organ̵7;s notes into a single integrated circuit chip, simplifying the instrument̵7;s design and lowering its cost.