Lossy

In-Depth Explanation

Lossy audio is a compression method that permanently discards audio data to reduce file size. Unlike lossless formats that reconstruct the original file bit-for-bit, lossy formats like MP3, AAC, and Ogg Vorbis remove frequencies and detail that human ears struggle to perceive. Once audio is encoded in a lossy format, the discarded information cannot be recovered. File sizes shrink by up to 90% compared to uncompressed WAV.

How Lossy Compression Works

Lossy codecs use a technique called perceptual coding. The codec analyzes the audio signal and identifies sounds that are masked by louder frequencies nearby. This is based on the principle of auditory masking: when two sounds occur simultaneously, the louder one makes the quieter one inaudible to the human ear. The codec discards the masked sound because the listener cannot hear it anyway.

The process works in four steps:

1. Transform: The codec splits the audio into frequency bands using a modified discrete cosine transform (MDCT).
2. Analysis: A psychoacoustic model evaluates each band and determines which sounds are masked and which are audible.
3. Quantization: The codec reduces the precision of the data in each band. Audible bands keep more bits. Masked bands get fewer bits or are discarded entirely.
4. Encoding: The reduced data is packed into the final compressed file using Huffman coding.

The result is a file that sounds close to the original to most listeners but contains significantly less data. The trade-off is permanent: converting the lossy file back to WAV restores the file size but not the discarded frequencies.

Common Lossy Formats in 2026

• AAC (Advanced Audio Coding): The dominant lossy codec for music streaming. Apple Music uses AAC at 256 kbps. YouTube and most video platforms use AAC for audio tracks. AAC is more efficient than MP3, meaning it sounds better at the same bitrate.
• MP3 (MPEG-1 Audio Layer III): Still the most universally compatible lossy format, supported by every device and player. At 320 kbps, MP3 approaches transparency. Below 192 kbps, artifacts become audible. MP3 is less efficient than AAC and Opus.
• Ogg Vorbis: Used by Spotify for its non-lossless streaming tiers. Spotify Premium streams Ogg Vorbis at up to 320 kbps. Spotify Free streams at 128 kbps on desktop and 96 kbps on mobile.
• Opus: The most efficient lossy codec available in 2026. Used by YouTube Music, Discord, and real-time communication platforms. Opus outperforms AAC and MP3 at bitrates below 128 kbps and matches them at higher bitrates.

Real-World Example

You export a 4-minute song as a 24-bit/44.1 kHz WAV file. The file is 45 MB. Here is what happens when you encode it to different lossy formats:

At 320 kbps MP3, the codec discards frequencies above approximately 16 kHz. Most adults cannot hear above 15 kHz, so the loss is imperceptible to casual listeners. At 128 kbps, the codec discards frequencies above approximately 12 kHz and reduces stereo separation. Trained ears on studio monitors hear the difference immediately.

The real danger is generation loss. If you encode the 320 kbps MP3 to AAC at 256 kbps, then someone uploads that to YouTube which encodes it to Opus at 128 kbps, the audio has been compressed three times. Each pass discards more data. The result sounds muffled, phasey, and lifeless compared to the original WAV.

Why It Matters for Independent Artists

1. Never upload lossy files to your distributor. Always upload 24-bit WAV files. If you upload an MP3, the streaming platform encodes it again to its own lossy format. This double compression causes audible degradation, especially in high frequencies and transient detail.
2. Archive in lossless only. Store your final masters as WAV or FLAC. If you ever need to remaster or re-release, you need the full-resolution source. A 320 kbps MP3 cannot be restored to its original quality.
3. Master with codec preview. Before releasing, use a codec preview tool (like iZotope Ozone 11's Codec module) to hear how your master sounds after AAC and Ogg Vorbis encoding. If the high frequencies sound dull after encoding, you may need to boost the 8 to 12 kHz range slightly in your EQ to compensate.
4. Understand what your listeners hear. As of 2026, Spotify Free streams at 128 kbps. Apple Music streams AAC at 256 kbps. YouTube Music streams Opus at 256 kbps. If a large portion of your audience uses Spotify Free, they hear your music at 128 kbps. Make sure your mix translates at that bitrate.
5. Use lossy formats only for their intended purpose. MP3s are fine for emailing demos, embedding in websites, or sending promo copies where file size matters more than fidelity. They are not acceptable as masters, archive copies, or distributor uploads.

Read our guide on mastering for streaming platforms to understand how lossy encoding affects your masters on each platform, and our music distribution services comparison to verify which distributors accept and deliver high-quality source files.

Related Terms

• Lossless - The counterpart to lossy: compression that preserves all audio data
• Codec - The software that performs lossy or lossless encoding and decoding
• Bitrate - The data rate that determines how much information a lossy codec retains
• Bit Depth - The resolution of the source file before lossy encoding
• Sample Rate - The frequency resolution of the source file before lossy encoding