Why is mastering audio specifically for streaming platforms different from mastering for CD?

Mastering for streaming platforms differs from mastering for CD primarily because streaming services use compression algorithms that alter the audio's dynamic range and overall sound. CD mastering aims for the highest possible dynamic range and sonic quality, assuming a direct, uncompressed playback. Streaming platforms, however, convert audio files into compressed formats like Ogg Vorbis (Spotify) or AAC (Apple Music) to reduce file size and bandwidth usage. This compression can introduce artifacts, reduce dynamic range, and alter the perceived loudness of the track. Mastering for streaming accounts for these compression effects by optimizing the audio's loudness, EQ, and dynamics to sound best after the streaming platform's processing. This often involves aiming for a specific LUFS (Loudness Units relative to Full Scale) target and ensuring the track translates well across different listening devices and environments. For example, a track mastered too loud for streaming might experience harsh clipping or distortion when compressed, whereas a track mastered at an optimal loudness level will maintain its clarity and impact.