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How-to Correct Loudness

Loudness correction for your media

Manage Loudness

The Dolby.io Media Enhance API allows you to correct and update your media to conform with loudness recommendations. Many popular streaming platforms enforce a limit that does not understand creative intent and the content creation process. The Media Enhance API allows you to ensure an even loudness across a collection with better results.

When you make a request to the /media/enhance endpoint you can specify custom parameters.

Sample Request

curl -X POST https://api.dolby.com/media/enhance \
  --header "x-api-key: $DOLBYIO_API_KEY" \
  --data '{
    "input": "dlb://in/example.mp3",
    "output": "dlb://out/example-spotify.mp3",
    "content": {
      "type": "podcast"
    },
    "audio": {
      "loudness": {
          "target_level": -18,
          "speech_threshold": 15,
          "peak_reference": "sample",
          "peak_limit": "-2"
      }
    }
  }'

target_level

The target_level in this example is set to -18. The value you use will depend on the type of content you are producing, how it will be delivered, and what devices it will be played back on. You want to choose a loudness target to match the desired outcome. Some rules of thumb:

  • Podcasts are often targeted to be between -16 to -18 LKFS
  • Music streaming services usually require content to conform to -14 LKFS
  • Television playback often limits loudness to -23/-24 LKFS based on regional standards

The pre-defined loudness profiles can be a useful reference if trying to conform to a specific platform or device.

speech_threshold

The speech_threshold is a way to tune the Dolby Dialog Intelligence speech-gated loudness measurement. See Gating Techniques for more background. The reported loudness measurement could be slightly off if you have mixed-media content so
explicitly setting this value based on your understanding of the content can yield better results.

peak

Setting the correct peak_limit reduces clipping and distortion. Many standards and delivery specifications with platforms specify a maximum sample-peak / true-peak level. If you exceed that level it will be rejected, so setting this value pro-actively helps insure successful delivery.

Finally, peak_reference gives control over whether to use the sample peak or the true_peak as the highest level of the waveform. True peak is a more accurate representation for the audio but sometimes delivery specs will call for a sample peak limit.


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