Bitrate settings like 128kbps and 320kbps show up in almost every audio export dialog, but the numbers rarely come with an explanation of what they're actually doing to the sound. Bitrate measures kilobits of data used per second of audio; a lossy format like MP3 or AAC uses that budget to approximate the original waveform, and a lower budget means more aggressive approximation, which shows up as audible loss in specific, predictable ways.
What actually gets discarded at lower bitrates
Lossy audio codecs use psychoacoustic modeling, they discard the parts of a sound humans are least likely to notice, based on how the ear perceives frequency and masking (a loud sound at one frequency hides quieter nearby sounds). At 320kbps, there's enough data budget that very little needs to be discarded, and most listeners can't distinguish it from the original. At 128kbps, the codec has to be far more selective, cutting high-frequency detail, cymbal shimmer, reverb tails, and subtle stereo separation first, since those are statistically least likely to be missed, though on complex, cymbal-heavy or classical music the loss becomes audible as a slightly dull, congested sound.
When the difference actually matters
For spoken-word content like podcasts, audiobooks, and voice memos, the difference between 128kbps and 320kbps is rarely audible, since speech occupies a narrower frequency range and has less of the fine detail bitrate reduction affects. For music, especially dense mixes with cymbals, layered synths, or wide stereo effects, the gap becomes more noticeable, particularly on headphones or quality speakers rather than a phone's built-in speaker. If file size matters more than archival quality, the Compress Audio tool can target a lower bitrate specifically for voice content, while music intended for critical listening is usually worth keeping closer to 256-320kbps.
Common bitrates at a glance
64kbps is roughly the floor for intelligible speech and is mainly used for low-bandwidth streaming; 96kbps is a common podcast/voice-memo export setting; 128kbps is the old default for casual music listening on early MP3 players and is still a reasonable minimum for music today; 192kbps is a solid general-purpose setting that's close to transparent for most listeners; 256kbps is what streaming services like Spotify and Apple Music typically use for their standard-to-high tiers; 320kbps is the maximum MP3 bitrate and the usual choice when file size genuinely doesn't matter. The estimator below turns any of these into an actual file size for a given track length, and the Audio Duration Calculator and Audio Metadata Viewer are useful for checking a specific file's existing length and encoding before you decide whether to re-encode it.