The information from the transducer element is a continuous flow of data. In signal processing, sampling is the reduction
of a continuous signal to a discrete signal.
A common example is exactly what we do in the ME70 system: conversion of a sound wave (which is a continuous-time signal) to a sequence of samples (a discrete-time signal).
A discrete (or discrete-time) signal is a sequence of data capsules, typically a signal that has been sampled from a continuous-time
signal. Unlike a continuous signal, a discrete signal is not a function of a time argument, but a sequence of quantities;
that is, a function over a domain of discrete integers. Each value in the sequence is called a sample.
In this coordinate system, the Y-axis is voltage (or “volume”) and the X-axis is time.
|
A |
is a continuous flow of data, an analogue signal, for example an echo. |
|
B |
identifies the samples that the system is extracting from the analogue signal. |
Each sample is identified with the time it was taken, and it will contain the value of the analogue signal at that time. The
time between each sample (C) is identified as the sampling frequency. Using this technique, the analogue signal is converted to a stream of discrete signals.
The sample frequency in the ME70 system is 62.5 kHz. Since the sound travels approximately 750 meter back and forth every second, each sample will cover 750
m divided by 62500 Hz, which is approximately 1.2 cm.