What is lossy audio?
Lossy audio refers to a type of audio compression that reduces file sizes by removing some of the audio data. While lossy compression can significantly decrease file sizes, making them easier to store and distribute, it often comes at the cost of audio quality, as the lost data can lead to a reduction in sound fidelity. The term "lossy" is derived from the fact that once this data is removed, it cannot be recovered or restored. The audio file is permanently altered, and the lost data is gone forever.
The data removed during the lossy compression process is typically the information least likely to be noticed by the human ear. This is based on the principle of psychoacoustics, which studies how humans perceive sound. By removing the data our ears are least likely to pick up on, lossy compression can achieve smaller file sizes while maintaining a level of audio quality that is acceptable to most listeners.
Psychoacoustics and lossy compression
Psychoacoustics is a field of study that seeks to understand how humans perceive sound. It examines how we interpret different frequencies, volumes, and other aspects of sound. This understanding of human auditory perception is very important to the process of lossy compression.
When an audio file is subjected to lossy compression, the algorithm used will typically remove the data our ears are least likely to perceive. This can include sounds at very high or very low frequencies, or sounds masked by louder sounds. By removing this inaudible data, lossy compression can reduce file sizes while maintaining a level of audio quality that is acceptable to most listeners.
Bit rate and lossy compression
One of the main factors in lossy audio compression is the bit rate. The bit rate refers to the amount of data processed per unit of time, typically measured in kilobits per second (kbps). A higher bit rate means more data is processed, resulting in higher audio quality but also larger file sizes.
In lossy compression, the bit rate can often be adjusted by the user. Lowering the bit rate will result in a smaller file size but also a greater loss of audio quality. Conversely, increasing the bit rate will result in a larger file size but less data loss and therefore higher audio quality. This allows users to balance their need for small file sizes with their desire for high-quality audio.
Common lossy audio formats
Several common audio formats use lossy compression. These include MP3, AAC, and Ogg Vorbis. Each of these formats uses a different algorithm for compression, resulting in different levels of audio quality and file size.
MP3 is perhaps the most well-known lossy audio format. It was developed in the 1990s and quickly became the standard for digital music distribution. AAC (Advanced Audio Coding) is another common lossy format and is the default audio format for many Apple products. Ogg Vorbis is a free and open-source lossy format often used for streaming audio.
MP3
MP3 (MPEG-1 Audio Layer III) is a lossy audio format developed by the Moving Picture Experts Group (MPEG) in the 1990s. It quickly became the standard for digital music distribution, thanks to its ability to significantly reduce file sizes while maintaining acceptable audio quality.
MP3 uses a complex algorithm to analyze the audio data and remove the information least likely to be noticed by the human ear. The degree of compression (and therefore the amount of data loss) can be adjusted by the user, allowing for a balance between file size and audio quality.
AAC
AAC (Advanced Audio Coding) is another common lossy audio format. It was developed as a successor to MP3, with the aim of providing better audio quality at similar bit rates. AAC is the default audio format for many Apple products, including iTunes and the iPod.
Like MP3, AAC uses a complex algorithm to analyze the audio data and remove the information least likely to be noticed by the human ear. However, AAC is generally considered to provide better audio quality than MP3 at similar bit rates, making it a popular choice for many users.
Ogg Vorbis
Ogg Vorbis is a free and open-source lossy audio format often used for streaming audio. It was developed by the Xiph.Org Foundation, with the aim of providing a free alternative to proprietary formats like MP3 and AAC.
Ogg Vorbis uses a different algorithm than MP3 and AAC, but the principle is the same: analyze the audio data and remove the information least likely to be noticed by the human ear. Ogg Vorbis is generally considered to provide good audio quality, and its open-source nature makes it a popular choice for many applications.
