Audio Engineering

Representation of Audio Signals 445

Vcc

10k 10k

A

B D

&

&

Inputs

Convention and good practice is to use pull-up resistors

on open gate inputs.

A 0 0 1 1 1

0

1

1

0

1

1

1

1

0

0

1

0

0

1

1

Metastable state

No change

No change

BCD

Outputs

Figure 15.4 : A simple latch. In this example, the outputs of each of two NAND gates are

cross coupled to one of the other inputs. The unused input is held high by a resistor to the

positive supply rail. The state of the gate outputs will be changed when one of the inputs is

grounded and this output state will be steady until the other input is grounded or until the

power is removed. This simple circuit, the R-S fl ip-fl op, has often been used to debounce

mechanical contacts and as a simple memory.

arrangements produce the wide range of fl ip-fl op (FF) gates, including the set–reset latch,
the D-type FF, which is edge triggered by a clock pulse, the JK FF and a wide range of
counters (or dividers), and shift registers ( Figure 15.5 ). These circuit elements and their
derivatives fi nd their way into the circuitry of digital signal handling for a wide variety of
reasons. Early digital circuitry was based around standardized logic chips, but it is much
more common nowadays to use application-specifi c ICs.

15.4 The Signifi cance of Bits and Bobs ........................................................................

Groupings of eight bits, which represent a symbol or a number, are usually referred
to as bytes, and the grouping of four bits is, somewhat obviously, sometimes called a
nibble (sometimes spelt nybble). Bytes can be assembled into larger structures, which