LAME cVBRb: what does bitrate boost change?
cVBRb adds bitrate-boost behaviour to the constrained VBR mode. These matched tests show how much the output bitrate and file size increase at three useful quality levels.
LAME cVBRb quality
cVBRb: constrained VBR with bitrate boost
cVBRb starts from the same -V quality target and strict -b minimum, then adds --bitrate-boost to apply extra bitrate pressure where the branch allows it.
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-frequency reach |
|---|---|---|---|
-V0 -b 192 --vbr-min-strict --bitrate-boost=3 | 260.8 kbps | 1.87 MiB/min | No default low-pass |
-V2 -b 160 --vbr-min-strict --bitrate-boost=3 | 196.3 kbps | 1.41 MiB/min | about 19.2 kHz |
-V4 -b 128 --vbr-min-strict --bitrate-boost=3 | 155.9 kbps | 1.12 MiB/min | about 17.8 kHz |
Maximum-quality example:
-V0 -b 192 --vbr-min-strict --bitrate-boost=3 averaged about 260.8 kbps across the three sources and about 1.87 MiB/min.How much does boost change the result?
In the matched tests, adding boost 3 increased average output from about 147.0 to 155.9 kbps at V4, 186.3 to 196.3 kbps at V2, and 248.1 to 260.8 kbps at V0. The size increase follows the additional bitrate rather than changing the basic V quality scale.
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 cVBRb settings and switch between them without restarting playback.
The listening test opens with this mode already selected.
Open the cVBRb listening testCommon questions
What is cVBRb?
cVBRb is the constrained VBR branch with additional bitrate-boost behaviour.
What does --bitrate-boost=3 do?
It is the strongest boost level used in these tests. It raises the resulting average bitrate compared with the matched cVBR setting.
What does the V0 cVBRb setting produce?
With -V0, a strict 192 kbps minimum and boost 3, the three sources averaged about 260.8 kbps and about 1.87 MiB per minute.