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April 27 2012

Automatic gain adjustment


We implemented a feature which automatically adjusts the level on the output audio material to compensate for inherent differences in preset levels, for example between clean and distorted guitar sounds. This enables us to achieve a consistent audio level across the range of presets for a given equipment, specially usefull when exploring the Library.

How it works

This feature is mostly implemented on the voind client, which is the program that directly interfaces with the audio equipment. This program periodically contacts the voind server and receives instructions needed to complete the task like pointers to the input midi/audio files, the equipment and preset to be used, whether the output should be cached at the voind client, etc.

With this new feature additional instructions are sent to the client which include:
  • The desired level (in dbFS) of the output audio file
  • Whether the level of the output file should match the audio input
  • The maximum level of gain that should be applied to the audio output

After the voind client processes the task, information sent back to the voind server reports:
  • The measured maximum level of the audio output
  • The actual gain applied to the audio output

Automatic gain adjustment in action

Input audio - a dull unprocessed mono guitar riff

Without automatic gain adjustment

Note how you are tempted to reach for the volume control for a confortable listening comparison between the two presets.
Stereo output audio for a clean guitar preset
Behringer V-AMP Pro, Bank 1, Patch 1
Stereo output audio for a distorted guitar preset
Behringer V-AMP Pro, Bank 1, Patch 7

With automatic gain adjustment

A much more consistent listening volume is achieved between the two presets
Stereo output audio for a clean guitar preset
Behringer V-AMP Pro, Bank 1, Patch 1

Target level: -4.75 dbFS
Gain Applied: 1.71 db
Stereo output audio for a distorted guitar preset
Behringer V-AMP Pro, Bank 1, Patch 7

Target level: -4.75 dbFS
Gain Applied: -4.76 db

Current limitations and next developments

Currently the maximum amount of gain that will be applied to the audio signal is limited to +/-6 db. This is to prevent excessive amplification of noise on low level material and loss of audio resolution on high level audio signals.

Target levels are fixed at -5 dbFS for quick orders, and for regular orders at -6 dbFS for Midi or tied to the level of input for audio orders.

We are also planning to give the User control on how the automatic gain adjustment is applied for regular orders.