Audio Engineering

Representation of Audio Signals 451

5V

4V

Clock waveform

3V

2V

1V

5V

4V

Data waveform

3V

2V

1V

Figure 15.7 : A practical problem arose where the data signal was intended to be clocked in

using the rising edge of a separate clock line, but excessive ringing on the clock line caused

the data line to be sampled twice, causing corruption. In addition, due to the loading of a

large number of audio channels, the actual logic level no longer achieved the 4.5-V target

required for acceptable noise performance, increasing the susceptibility to ringing. The

other point to note is that the falling edge of the logic signals took the data line voltage to a

negative value, and there is no guarantee that the receiving logic element would not produce

an incorrect output as a consequence.

important because of the effect on integrity. The outline of the problem is shown in Figure
15.7 , which has been taken from a practical problem in which serial data were being
distributed around a large digitally controlled audio mixing desk. Examples such as this
illustrate the paradox that digital signals must, in fact, be considered from an analogue
point of view.

15.6 The Analogue Audio Waveform ...........................................................................

It seems appropriate to ensure that there is agreement concerning the meaning attached to
words that are freely used. Part of the reason for this is in order that a clear understanding
can be obtained into the meaning of phase. The analogue audio signal that we will
encounter when it is viewed on an oscilloscope is a causal signal. It is considered as
having zero value for negative time and it is also continuous with time. If we observe a