Using VLevel

VLevel currently works in two ways: as a filter (similar to cat or sort), and as a LADSPA plugin. The filter is installed as /usr/local/bin/vlevel-bin, and the plugin is installed as /usr/local/lib/ladspa/vlevel-ladspa.so.

Filter

The command line filter is called vlevel-bin. It currently only accepts 16-bit little-endian data, but you can specify the number of channels with the --channels option. You can find out more with the --help option. There are some useful scripts in the docs/ folder. Here are some examples:

See a summary of arguments
vlevel-bin --help

VLevel and play infile.ogg
ogg123 -d raw -f - infile.ogg | vlevel-bin | artscat

VLevel infile.wav and save as outfile.wav
sox infile.wav -t raw - | vlevel-bin | sox -t raw -r 44100 -c 2 -ws - outfile.wav

VLevel all .ogg files in current directory
docs/vlevel-dir

Plugin

LADSPA is a plugin architecture, and a LADSPA plugin like VLevel works with any program that can load LADSPA plugins. For a partial list of such programs, see the LADSPA site. Though not on that list, XMMS can use VLevel and other LADSPA plugins via XMMS LADSPA. Many programs don't need this, but if the plugin isn't found, add /usr/local/lib/ladspa to the LADSPA_PATH environment variable.

Settings

Look-Ahead

This controls how much audio VLevel will buffer, and long before a volume change VLevel will start compensating. If the look-ahead is 2 seconds, VLevel will begin ramping the volume down 2 seconds before a loud part is played. In the LADSPA plugin, the units are seconds. In the filter, the units are samples, so for for a 2 second buffer of 44.1 kHz audio, the argument would be "--length 88200".

Strength

This controls how much VLevel changes the data. If it is 0, the volume will not be changed at all. If it is 1, every sound will be the same volume. I use .8, but it's a matter of preference. This corresponds to the filter's --strength argument.

Maximum multiplier

VLevel doesn't make loud parts quieter, it makes quiet parts louder. When audio is output, it is multiplied by the multiplier, and the multiplier changes so that the output sample is never clipped. To keep static from becoming audible, you can limit this with maximum multiplier. Settings between 10 and 20 work well. When using the plugin, make sure you set Use Maximum Multiplier. This corresponds to the filter's --max-multiplier setting, and negative values disable it.

Undo

Although the results aren't perfect, it's possible to undo the effects of VLevel by setting this. Use the same strength as you first used to VLevel. To undo with the filter, you must set strength to s / (s - 1), where s is the strength you originally used. For more information, see the Technical section.

Current Multiplier

This plugin output simply shows you how much the samples are currently being multiplied by. It's useful for finding the right strength and multiplier limit. It always changes gradually, especially with large look-ahead settings.