Digital silence

Overview

The term "digital silence" is used to describe a digital audio signal which contains all "zeroes;" and therefore represents complete silence.

History

Digital silence is directly related to CD technology because it is part of the commercial format “Red Book” standard. In order to assure that there were no noises when the CD started or ended playing; there must be complete silence at the beginning and end of the CD audio file. This was to allow for the use of “muting relays” in the audio output circuitry of the CD player to prevent undesired noise from being output during power on/off. If there is any signal present when the relay contacts open or close, a “pop” or “thump” could occur in the audio output. Even a relatively low level DC “offset” could cause a “pop;” so the simple way to address this was to specify that “digital silence” be present when the relay contacts would be opening or closing. DC offset was actually a common problem in early converter designs; so it was not unusual for these early digital recordings to have at least some DC present.

Basics

Although analog audio circuits can be designed to be extremely "low-noise" and therefore have no perceivable sound present unless amplified to an usually high level; there is always some noise present at the lowest levels. In digital audio; it is possible to have "complete silence" as represented by every bit in the digital audio word being a "0". When reproduced by a DA converter; digital silence will cease to be absolute because of real-world limitations regarding noise in analog circuitry.