This conversion between analog and digital takes a short amount of time, which is known as latency. Although this process consumes a very small interval, it can have a cumulative effect if the data is handed off by several layers of software.
One example of latency is a musical keyboard connected to a computer. When the user hits a key, an audio signal, which is analog, is transferred along the connecting wire in the form of electrical current. The computer would then convert the signal to a digital format and process it according to any settings input by the user. After the processing is complete, the processed digital signal is converted to an analog sound wave (represented by current in the wire), which is then sent to the speaker.
Digital conversion processes include analog-to-digital converters (ADC), digital-to-analog converters (DAC), and various changes from one digital format to another, such as AES3 which carries low-voltage electrical signals to ADAT, an optical transport. Any such process takes a small amount of time to accomplish; typical latencies are in the range of 0.2 to 1.5 milliseconds, depending on sampling rate, bit depth, software design and hardware architecture.
DSP can take several forms; for instance, Finite impulse response (FIR) and Infinite impulse response (IIR) filters take two different mathematical approaches to the same end and can have different latencies, depending on the lowest audio frequency that is being processed as well as on software and hardware implementations. Typical latencies range from 0.5 to ten milliseconds with some designs having as much as 30 milliseconds.
Individual digital audio devices can be designed with a fixed overall latency from input to output or they can have a total latency that fluctuates with changes to internal processing architecture. In the latter design, engaging additional functions adds latency.
Latency in digital audio equipment is most noticeable when a singer's voice is transmitted through their microphone, through digital audio mixing, processing and routing paths, and then sent to their own ears via in ear monitors or headphones. In this case, the singer's vocal sound is conducted to their own ear through the bones of the head and then 1-5 milliseconds later through the digital pathway to their ears. This combination of bone conduction and digital latency is unsettling to some singers. Latency times under 2 ms and over 15-20 ms can reduce the annoyance.
Latency for other musical activity such as playing a guitar doesn't have the same critical concern. Ten milliseconds of latency isn't as noticeable to a listener who isn't hearing his or her own voice.