DAFX: Digital Audio Effects, Second Edition

12.6 Antiquing of Audio Files

In this section we discuss an algorithm to transform audio files to sound very old. The signal modeling approach is taken here, although the basis of many related algorithms lies in the physical principles of the underlying analog systems [VGKP08].

The antiquing methods introduce simulated degradations to audio signals. They can be divided into two general groups: global and localized degradations [GR98]. Global degradations affect all samples of the audio signal and contain effects such as background noise, wow and flutter, and certain types of nonlinear distortion. Localized degradations affect some signal samples, but not all of them. Examples of such a localized degradation would be the ‘clicks’ and ‘pops’ heard on a dusty vinyl record.

Since audio signals are often stereophonic, the first step in audio antiquing is usually to convert the audio signal into the monophonic form. The simplest method, which yields satisfactory results in most cases, is to average the two channels. However, some stereo recordings use special effects, such as time delay or inverted phase between the two channels, and in such cases the simple technique fails. In the worst cases one or more sources in the original signal can be cancelled or be strongly colored, when the channels are added together.

12.6.1 Telephone Line Effect

The telephone sound is a commonly used effect in music production and in film soundtracks. It is used in movies and TV series to process the actor's ...