Before you start

This guide assumes that you understand the basics of making a Music Mastering API request. We recommend completing the Getting Started with the Music Mastering API guide first.

Music Mastering Preview metrics

When you process your music file with the Music Mastering Preview API, you can learn about your original music file media format, loudness, EQ, and stereo image using the returned metrics. The metrics will help you better understand your music file before processing it with the Music Mastering API. You may find that your original music file was set at an incorrect sampling rate, the file was accidentally exported in mono instead of stereo, or was mixed too loudly. In addition to learning the details of your music files, you can use the Music Mastering Preview metrics for content analysis to set a standard for your platform's quality control.

The following Container, Audio, Loudness, EQ, and Stereo image descriptions correspond to the Example Music Mastering Preview metrics.

Container

The container information includes details about the music file's container.

• kind: a description of the type of media container.
• duration: the media duration (in seconds).
• bitrate: media bitrate (in bits per second).
• size: media size (in bytes).

Audio

The audio information includes details about the music file's audio stream.

• duration: audio duration (in seconds).
• codec: identifier for the compression codec.
• sample_rate: audio sample-rate, generally 44100 or 48000.
• bitrate: audio bitrate (in bits per second).
• channels: the number of channels, generally mono (1) or stereo (2).
• channel_order: a comma separated list of channel identifiers if there are more than two channels.
• bit_depth: 16, 24, or 32-bit.

Loudness

The loudness information includes details about the music file's loudness before processing.

• measured: level of the input file prior to mastering. Measured in loudness units relative to full scale (LUFS).
• range: loudness range of the input file prior to mastering. Measured in loudness units (LU).
• true_peak: true-peak of the input file prior to mastering. Measured in decibel True Peak (dBTP).

EQ

The EQ information includes details about the music file's EQ before processing.

• levels: amplitude values of the input file's EQ broken up into 16 bands centered at 20, 31.7, 50.2, 79.6, 126, 200, 317, 502, 796, 1260, 200, 3170, 7960, 12600, and 20000 Hz. Measured in dB.

Stereo image 

The stereo image information includes details about the music file's stereo image before processing. Stereo image is the perceived spatial location of sound elements in a track.

• The width metrics indicate the perceived spatial distance of the stereo sound. These metrics are continuous values that range from -1.0 (very narrow, close to mono) through 0 (well balanced) to 1 (excessively wide). The metric is provided in the low, mid, and high-frequency bands where:
  • low: 0 to 120 Hz.
  • mid: 120 to 1500 Hz.
  • high: 1500 to the upper frequency limit (for example, input sampling rate / 2).

Example Music Mastering Preview metrics

The following example shows the metrics that are returned from the Music Mastering Preview API. The returned metrics about your original music file include media format, loudness, EQ, and stereo image.

{
    "media_info": {
        "container": {
            "kind": "wav",
            "duration": 184.271,
            "bitrate": 1411220,
            "size": 32505868
        },
        "audio": {
            "codec": "pcm",
            "bit_depth": 16,
            "channels": 2,
            "sample_rate": 44100,
            "duration": 184.271,
            "bitrate": 1411200
    },
    "audio": {
      "loudness": {
        "measured": -9.3,
        "range": 8.2,
        "true_peak": -0.5,
      },
      "eq":{
          "levels": [-5.6, 0.3, -3.4, -1.1, 0.5, -5.6, 0.3, 0.0, -1.1, 0.5, -5.6, 0.3, -3.4, -1.1, 0.5, -0.2]
      },
      "spatial":{
        "stereo_image":{
            "width":{
                "low": 0.2,
                "mid": -0.08,
                "high": -0.25
            }
      }
    }