Each digital process—plug-in processing, changing the volume or pan level, and so on—adds an amount of latency (a small delay). Each of these processing latency values is added to each other.
To explain, a software instrument running inside Logic Pro will only have an output latency, because it is generated inside the application. An audio recording that is being monitored in real time will have both an input, and an output, latency. These two values are summed, resulting in an overall monitoring latency figure.
Each process—such as the use of an effect plug-in, for example—will also add an amount of latency, which is combined with the input and output latency figure, depending on whether a software instrument or audio channel strip is in use. For example, if a recorded vocal is routed through a compressor effect (with a 10 millisecond latency) and the audio interface output latency is 40 milliseconds, the total latency figure would be 50 milliseconds (10 + 40 = 50). If three plug-ins (reverb, chorus, and compressor, for example) that also introduced a 10 millisecond latency were used for this track, the latency would be 70 milliseconds (10 + 10 + 10 + 40 = 70).
The audio interface input and output latency is handled by the settings in the Logic Pro > Preferences > Audio > Devices pane (see Configuring Your Audio Hardware). Internal latencies introduced by plug-ins are dealt with in a different way, which is the focus of this chapter.