Audio signal

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An audio signal is a representation of sound waves in a different form. Typically this is an electrical voltage, but it can be magnetic, when recorded onto analogue tape, for example, or as radio waves. An audio signal can be manipulated, stored, transmitted and reproduced in ways that a sound wave cannot.

Microphones convert sound pressure waves into voltage, an electrical audio signal. Therefore you find the microphone sensitivity as millivolts per pascals. Speakers or headphones convert an electrical audio signal into sound. Although many audio signals have their origin as a sound wave, devices such as synthesisers are designed to create audio signals.

Electric energy flows through a circuit as voltage. The opposition to voltage is impedance. Impedance is measured in ohms. In professional audio, the lower the impedance of a circuit, the better. To measure electric energy in an audio signal, decibels are used in relation to either power (dBm) or voltage (dBu or dBv, and dBV). dBm was originally used, but is no longer as popular as the other units.

[edit] Signal flow

Signal flow is the term used to describe the path an audio signal will take from source (microphone) to the speaker or recording device. It is most frequently in a recording studio setting, where the signal flow is often very long and convoluted as the electric signal may pass through many sections of a large analog console, external audio equipment, and even different rooms.

[edit] Digital equivalent

As much of the older analog audio equipment has been emulated in digital form, usually through the development of audio plug-ins for Digital Audio Workstation (DAW) software such as Pro Tools or Logic, the terms audio signal and signal flow are also used to describe the path of digital information through the DAW (ie. from an audio track through a plug-in, sent a bus and an aux, and out a hardware output).

Digital audio signal being sent through wire can use several formats including optical (ADAT, TDIF), coaxial (S/PDIF), XLR (AES/EBU), and ethernet, especially for large digital audio consoles.