What Is Audio Bitrate? Definition and Guide
Bitrate tells you how much audio data is processed per second. Higher bitrate means more data, which usually means better sound. It is the single most important number when choosing audio quality settings.
Bitrate Defined
Bitrate is measured in kilobits per second (kbps). A 128 kbps MP3 uses 128,000 bits of data for every second of audio. A 320 kbps MP3 uses 320,000 bits per second — more than double the data. More data means the encoder can represent the audio more accurately. It can keep more of the subtle details that lower bitrates discard. Bitrate directly determines file size: a 128 kbps file is half the size of a 256 kbps file, all else being equal.
How Bitrate Affects Quality
Below 96 kbps, most people hear obvious compression artifacts — swirly, underwater sounds on cymbals and high frequencies. At 128 kbps, quality is acceptable for casual listening and speech. At 192 kbps, quality is good enough that most listeners cannot distinguish it from CD on consumer headphones. At 256-320 kbps, the audio is transparent for virtually all listeners in all conditions. Beyond 320 kbps in lossy formats, you are wasting space — the codec cannot use the extra bits effectively.
Bitrate and File Size
The math is simple. Bitrate times duration equals file size. A 128 kbps file runs about 1 MB per minute. A 320 kbps file runs about 2.4 MB per minute. A three-minute song at 128 kbps is roughly 3 MB. The same song at 320 kbps is roughly 7.2 MB. Uncompressed CD audio (WAV) runs at 1,411 kbps — about 10 MB per minute. FLAC compresses this to roughly 700-900 kbps with no quality loss.
Choosing the Right Bitrate
For podcasts and voice: 96-128 kbps MP3. Speech does not need high bitrates. For music streaming: 192-256 kbps. This is what most services use. For archival MP3: 320 kbps. Maximum quality within the MP3 format. For professional work: Skip bitrate entirely and use lossless (WAV or FLAC). For mobile with limited storage: 128-192 kbps is the practical sweet spot between quality and space. Match the bitrate to the listening context, not your audiophile aspirations.
CBR vs VBR Bitrate
CBR (constant bitrate) uses the same bitrate throughout. Simple but wasteful — quiet passages get the same data as complex ones. VBR (variable bitrate) allocates more bits to complex passages and fewer to simple ones. Result: better quality at the same average file size. ABR (average bitrate) targets an average but varies moment to moment. For MP3, VBR with LAME's V2 preset (roughly 190 kbps average) is widely considered the best quality-to-size ratio.