Dynamic Range Control
The dynamic range of a signal is defined as the logarithmic ratio of maximum to minimum signal amplitude and is given in decibels. The dynamic range of an audio signal lies between 40 and 120 dB. The combination of level measurement and adaptive signal level adjustment is called dynamic range control. Dynamic range control of audio signals is used in many applications to match the dynamic behavior of the audio signal to different requirements. While recording, dynamic range control protects the AD converter from overload or is employed in the signal path to optimally use the full amplitude range of a recording system. For suppressing low-level noise, so-called noise gates are used so that the audio signal is passed through only from a certain level onwards. While reproducing music and speech in a car, shopping center, restaurant or disco the dynamics have to match the special noise characteristics of the environment. Therefore the signal level is measured from the audio signal and a control signal is derived which then changes the signal level to control the loudness of the audio signal. This loudness control is adaptive to the input level.
Figure 7.1 shows a block diagram of a system for dynamic range control. After measuring the input level XdB(n), the output level YdB(n) is affected by multiplying the delayed input signal x(n) by a factor g(n) according to
The delay of the signal x(n) compared with the control signal g(n) allows predictive ...