What Makes an Audio Format Lossy?

Save disk space with lossy audio files

Unhappy girl listening to the music in the city

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The word lossy is used in digital audio to describe a type of compression used to store sound data. The algorithm used in a lossy audio format compresses sound data in a way that discards some information. This signal loss means that the encoded audio isn't identical to the original. The lossy audio produces a lower quality sound and has a smaller file size.

Lossy compression is also called irreversible compression because it's impossible to rebuild the data that's been stripped away.

What's the Difference Between Lossy and Lossless?

When you create a series of MP3 files by ripping one of your music CDs, some of the detail from the original recording is lost, making it lossy. This type of compression isn't restricted to audio; image files in the JPEG format, for example, are also lossily compressed.

This method is the opposite of lossless audio compression used for formats such as FLAC, ALAC, and others. The audio, in this case, is compressed in a way that doesn't discard any data at all. The audio is identical to the original source.

When it comes to compatibility, lossily compressed files are an advantage. While some devices and software programs support a wide variety of audio formats, lossy formatted files like MP3s work on any device.

Examples of Lossy & Lossless Audio File Types
Lossy Lossless
AA3 ALAC
AAC FLAC
MP3 APE
MPC SHN
OGG TTA
WMA WV

How Does Lossy Compression Work?

Lossy compression makes certain assumptions about frequencies that the human ear is unlikely to detect.

When a song is converted to a lossy audio format such as AAC, the algorithm analyses all the frequencies and then discards ones that the ear shouldn't be able to detect. These low frequencies are filtered out or converted to mono signals that take up less disk space.

Another technique discards very quiet sounds that a listener is unlikely to notice, especially in a louder part of a song. This approach reduces the size of the audio file while retaining as much audio quality as possible.

What Happens to Lossy Audio?

Lossy compression introduces artifacts. These artifacts represent undesirable sounds that aren't in the original recording but are by-products of compression. This noise degrades the quality of the audio and is noticeable when music files are converted using low bit rates.

Different types of artifacts affect the quality of a recording. Distortions are one of the most common artifacts. A distortion makes drums, for example, sound weak — without any real punch. Voices in a song can also be affected, leading to vocals that sound coarse and lack detail.

In many cases, ordinary listeners cannot detect the difference between a lossy and a lossless encoding algorithm, although some audiophiles using very expensive equipment claim to hear a difference. The quality difference becomes noticeable only when very low bit rates or aggressive compression algorithms come into play.

Why Compress Audio Files?

Most digital audio formats employ some sort of compression to store sound in an efficient way. Without compression, file sizes would be very large.

For example, a typical 3-minute song stored as an MP3 file consumes 4 MB to 5 MB of space. Using the WAV format to store this same song, but uncompressed, results in a file size of approximately 30 MB — at least six times larger. Fewer songs fit on your smartphone or hard drive when you choose uncompressed audio formats.

How to Compress Audio Files

There are lots of ways to turn a lossless audio file into a lossy one. Any program that converts to a lossy format includes the necessary tools to make the lossy audio file. Browse any list of free audio file converters and experiment with different apps that convert audio file formats to MP3 and other lossy formats. Different apps may produce different results.