# Adding dynamic range compression
<a name="drc-tag"></a>

*<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. 

![\[Dynamic range compression increases the volume of the sounds around a certain threshold.\]](http://docs.aws.amazon.com/polly/latest/dg/images/drc-on.png)


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>
```

**Note**  
When you use "`drc`" in the `amazon:effect `syntax, it is case-sensitive. 

**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. 

![\[Using the prosody volume tag increases the volume across the entire audio file.\]](http://docs.aws.amazon.com/polly/latest/dg/images/prosodyloud.png)


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.

![\[Using the drc tag with a prosody volume tag increases the volume of the middle-range sounds in addition to the volume of the entire audio track.\]](http://docs.aws.amazon.com/polly/latest/dg/images/prosody+drc.png)


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.

**Note**  
When using the `drc` and `prosody volume` tags together, use standard XML practices for nesting tags.