Understanding volume ramping

Volume ramping (or simply ramping) allows you to control volume changes.

Using volume ramping alleviates artifacts, such as clicks or pop sounds, that typically occur when a change in volume is too great over a short period of time. You can also use volume ramping to gradually change the volume to get a fade in or fade out effect. For example, if you have a voice subchannel that ducks the music that's playing on another subchannel, you may want to use volume ramping so that when the voice call completes, rather than starting the audio so that it plays almost immediately at its original volume, you may want to gradually increase the volume.

You can use multiple segments for your volume ramping ramp so that you can build a curve for the ramp. If you choose to use one segment, the volume ramps is linear. Each volume segment defines two values, delimited by a colon; while each segment is delimited by a comma:

• A percentage of the duration specified (expressed as a percentage value between 1 and 100) based on a configured number of samples (duration of time).
• A percentage of the overall volume delta to increase the volume. This is a linear increase in volume for the segment. The volume delta is the difference between the current volume level and the volume level before the subchannel was muted or paused.

You can define multiple segments, and the percentages that provide for the time to increase the volume and the amount to increase the volume by must total 100. Or you can define one segment, which specifies a liner ramp in volume.

The ramp duration is the time in milliseconds for the entire ramp, or the total number of ramp segments. It is a configured value that you provide in the audio policy configuration file. For more information, see the [vol_ramp] subsection in the Syntax of the audio policy configuration file section of this chapter.