LAME CBR: what does each -b bitrate produce?
CBR keeps the selected bitrate fixed. The table shows the resulting file size and the approximate high-frequency reach of the current encoder at practical stereo music rates.
LAME CBR quality
LAME CBR: what does each
CBR bitrate, file size and frequency range
With CBR, -b sets the fixed MP3 bitrate. This makes file size especially predictable.
Frequency context: the conventional human audible range is about 20 Hz–20 kHz, and CD audio is normally considered to cover that full audible range. A result close to 20 kHz therefore reaches the top of the usual audible-band reference. Frequency reach is only one part of MP3 quality; extra bitrate can also improve how accurately the retained audio is represented.
| LAME command | Average bitrate | Approx. file size | High frequencies tail off |
|---|---|---|---|
-b 96 | 96 kbps | 0.69 MiB/min | about 15.5 kHz |
-b 128 | 128 kbps | 0.92 MiB/min | about 17.1 kHz |
-b 160 | 160 kbps | 1.15 MiB/min | about 17.8 kHz |
-b 192 | 192 kbps | 1.38 MiB/min | about 19.2 kHz |
-b 224 | 224 kbps | 1.61 MiB/min | about 19.9 kHz |
-b 256 | 256 kbps | 1.83 MiB/min | about 19.9 kHz |
-b 320 | 320 kbps | 2.29 MiB/min | about 20.6 kHz |
Example:
lame.exe -b 192 input.wav output.mp3 produced 192 kbps CBR, about 1.38 MiB per minute, with the high-frequency response effectively tailing off around 19.2 kHz.What changes when CBR bitrate increases?
Higher CBR rates give LAME more data for each second of audio. The upper frequency limit generally rises with bitrate, but not every extra bitrate step increases it. In these tests, 224 and 256 kbps both extended to about 19.9 kHz — essentially the upper end of the conventional 20 Hz–20 kHz audible range. At 256 kbps, the additional bitrate is therefore available to represent the retained audio more accurately rather than simply extending its frequency range further.
How these figures were measured
Each setting was encoded with the current LAME 4.0 build against the same three stereo WAV sources. Average bitrate is the mean of the three encoder results. File size is normalized to MiB per minute so clips of different lengths can be compared fairly. The high-frequency figure is the approximate point where the default encoder response has effectively tailed off.
The three source WAV files are CC0 material from Freesound: Erokia 524947, Usilaya 546205, and astro_denticle 846944.
Listen to these settings
Hear the same source at different CBR settings and switch between them without restarting playback.
The listening test opens with this mode already selected.
Open the CBR listening testCommon questions
What does -b mean in LAME?
For CBR encoding, -b selects the bitrate in kilobits per second. For example, -b 192 selects 192 kbps CBR.
How big is a 192 kbps MP3?
In these tests, 192 kbps CBR used about 1.38 MiB per minute of audio.
What frequency range does a 128 kbps MP3 retain?
With the current LAME defaults used here, the high-frequency response effectively tailed off around 17.1 kHz at 128 kbps.