Audio Formats*

Audio formats can be categorized into 3 distinct groups. These are Uncompressed, Lossless, and Lossy files. Also, it helps to know the term PCM and how it applies to the different file types.

Bitrates

A bitrate is the number of bits conveyed or transferred in a unit of time. When talking about music formats, bitrate is used in kilobits per second (kbps). When comparing files with different bitrates (of the same song), the file with the higher bitrate has the higher quality. For example, an MP3 320kbps (CBR) file transfers 320 kilobits per second.

Bitrates Example

Uncompressed Lossless

Uncompressed lossless formats store all of the original recorded data. Since silence is given the same number of bits per second as sound is, uncompressed lossless files are huge. The main uncompressed lossless format is pulse-code modulation (PCM). For example:

Compressed Lossless

Compressed lossless formats store all of the original recorded data in less space than uncompressed lossless formats by compressing the data. By giving silence almost no bits per second and compressing sound, a compressed lossless file is usually half as big as the same song stored in an uncompressed lossless file.

Since both uncompressed lossless formats and compressed lossless formats retain all the data from the original recording, they can be transcoded between each other without a loss in quality. For example:

Compressed Lossless Example

Lossy

Lossy formats are always compressed. Lossy formats have smaller file sizes than both uncompressed lossless formats and compressed lossless formats because they remove some of the original data. Usually the removed data is in the higher frequencies that humans can't hear, however, there can be obvious audible differences between lossy formats and lossless formats.

Lossy formats CANNOT be transcoded into any other lossy format without losing more quality. It CANNOT be transcoded into lossless either, because it wouldn't be a true lossless file when the source medium is already lossy. Examples of lossy formats include:

File size

How big your audio file will be depends on the length of the audio as well as its bitrate. When the files are stored on disk, they take up a certain amount of space, the actual storage space needed is measured in bytes (or megabytes/gigabytes for larger files).

Transparency

Transparency is a term used to describe the audible quality of a lossy music file. A lossy file is considered transparent if the average human cannot tell the difference between the lossy file and a lossless file of the same song by just listening to both without knowing which file is which. For most people, MP3 192kbps (CBR) is considered transparent.

Transparency Example Casual Listener

Spatial Audio

Dolby Atmos

Dolby Atmos (EC-3/EAC3-JOC) is an advanced audio technology that allows sound to be precisely placed and moved in three-dimensional space, including overhead. It extends the concept of surround sound with added height channels, providing a more immersive audio experience.

  • Object-based audio format, where sound elements can be placed in any position within a 3D space.
  • Provides a dynamic and lifelike sound experience, enhancing the feeling of being inside the action.
  • Supported in theaters, home theaters, soundbars, headphones, and even mobile devices.
    • Dolby Atmos Example

    Dolby Digital

    Dolby Digital (also known as AC-3/AC-4 IMS) is a digital audio coding standard that compresses audio data to reduce the amount of space needed for storage and transmission. It is commonly used in DVDs, Blu-rays, and broadcast television.

  • Supports up to 5.1 channels of audio (five full-bandwidth channels and one low-frequency effects channel).
  • Provides high-quality sound with efficient compression.
  • Widely used in broadcast media.

    • Sony 360 Reality Audio

    Sony 360 Reality Audio (MHM1/MHA1) is an immersive audio format that uses object-based spatial audio technology to create a 360-degree sound field. This format aims to recreate the experience of being at a live concert or in a recording studio with sound coming from all directions.

  • Uses object-based audio to place individual sound sources around the listener in a 3D space.
  • Provides an immersive listening experience similar to Dolby Atmos but at (higher bitrates) focused on music rather than cinematic audio.
  • Compatible with selected headphones and speakers only, requires compatible decoder that supports the format.
    • Sony360_RA Example

    Binaural Audio

    Binaural audio is a method of recording sound that uses two microphones arranged to create a 3D stereo sound sensation for the listener. This recording technique is designed to mimic the way human ears hear, with the microphones placed at a distance that simulates the human head.

  • Creates an immersive listening experience, making the listener feel as if they are in the room where the sound was recorded.
  • Best experienced using headphones (Apple Airpods/Beats) [Head-Tracking]Technology
  • Used often in virtual reality (VR) and augmented reality (AR) applications.
    • Binaural Example

    Downmix

    Downmixing is the process of converting a multi-channel audio track (such as 5.1 or 7.1 surround sound) into a format with fewer channels (such as stereo or mono).

  • Ensures compatibility with different playback systems that may not support multi-channel audio.
  • Important for maintaining audio quality and balance when played on devices that do not support the original format.
  • Often used in broadcasting, streaming, and when creating home audio versions of theatrical releases.