Adding dynamic range compression

<amazon:effect name="drc">

This tag is supported by long-form, neural, and standard TTS formats.

Depending on the text, language, and voice used in an audio file, the sounds range from soft to loud. Environmental sounds, such as the sound of a moving vehicle, can often mask the softer sounds, which makes the audio track difficult to hear clearly. To enhance the volume of certain sounds in your audio file, use the dynamic range compression (drc) tag.

The drc tag sets a midrange "loudness" threshold for your audio, and increases the volume (the gain) of the sounds around that threshold. It applies the greatest gain increase closest to the threshold, and the gain increase is lessened farther away from the threshold.

This makes the middle-range sounds easier to hear in a noisy environment, which makes the entire audio file clearer.

The drc tag is a Boolean parameter (it's either present or it isn't). It uses the syntax: <amazon:effect name="drc"> and is closed with </amazon:effect>.

You can use the drc tag with any voice or language supported by Amazon Polly. You can apply it to an entire section of the recording, or for only a few words. For example:

<speak>
     Some audio is difficult to hear in a moving vehicle, but <amazon:effect name="drc"> this audio 
     is less difficult to hear in a moving vehicle.</amazon:effect>
</speak>

Using drc with the prosody volume Tag

As the following graphic shows, the prosody volume tag evenly increases the volume of an entire audio file from the original level (dotted line) to an adjusted level (solid line). To further increase the volume of certain parts of the file, use the drc tag with the prosody volume tag. Combining tags doesn't affect the settings of the prosody volume tag.

When you use the drc and prosody volume tags together, Amazon Polly applies the drc tag first, increasing the middle-range sounds (those near the threshold). It then applies the prosody volume tag and further increases the volume of the entire audio track evenly.

To use the tags together, nest one inside the other. For example:

<speak>
     <prosody volume="loud">This text needs to be understandable and loud. <amazon:effect name="drc">
     This text also needs to be more understandable in a moving car.</amazon:effect></prosody> 
</speak>

In this text, the prosody volume tag increases the volume of the entire passage to "loud." The drc tag enhances the volume of the middle-range values in the second sentence.