CAO for Loudness

Loudness CAO is used to improve the perception of audio. It is also referred to as Loudness Compensation or Loudness Equalization.

Human hearing sensitivity varies across different sound frequencies. This means when a audio is played at a certain volume it generates sound pressure level, due to this all the frequencies are not equally perceived at the same level. In order to address this and create a more evenly distributed perception throughout the sound spectrum, you need to apply gain to each frequency volume. The amount of gain needed depends on the overall volume of the audio.

Loudness CAO is designed to apply different gains at certain frequency bands. Amount of gain applied is based on Volume level. Usually, Gain is applied at low and high frequency bands, whereas more gain is applied at low volume levels.

The Loudness CAO is applied to the incoming audio before it is upmixed. This ensures the incoming audio is adjusted for loudness prior to upmixing.

In a system for optimal Loudness processing, the Loudness CAO need to be placed at the input side of the signal flow.

Loudness CAO uses below audio objects :

1. ToneControlExtended
2. LUT

ToneControlExtended: The Loudness CAO uses ToneControlExtended AO to apply the gain in certain frequency bands. 3-band ToneControlExtended is used here. “Freq”, “Gain” and “Q-factor” for each band of ToneControlExtended can be tuned to get desired frequency response. Tuning parameter Filter type for each band can be shelving or parametric.

LUT: The LUT is used to store the tuning parameters Freq, Gain and Q-factor of ToneContolExtended AO. Tuning parameters for different volume levels are stored in LUT table. There are 51 tuning steps, where each tuning step is 3 band Tone Control. The tuning step is selected based on ControlIn connected to LUT. The ControlIn pin has to be driven by volume control. ControlIn can take value from 0 to 100 corresponding to 0% or mute and 100 corresponds to 100% or full volume.

Refer below diagram for frequency response of loudness compensation (51 curves).

Loudness CAO is designed for stereo input and output.

Please refer the below SFD of Loudness CAO. In the SFD, ToneControlExtended AO is named as “Loudness3Bands_1_0_1”.

As of now, tuning panel is not available for Loudness CAO.