5.3. The RVA system

RVA stands for Relative Volume Adjustment, and refers to a system that is supposed to compensate for the fact that the perceived volume levels of tracks from different records are sometimes quite different. With usual players, you are left with the possibility to adjust the volume manually, when necessary; but not with Aqualung.

Besides having a fully-fledged system for RVA, Aqualung also supports using already existing ReplayGain or RVA information present in your audio files' metadata. If you are interested in this, read on, but make sure to also check out this section.

You have to do two things prior to using RVA in Aqualung. First, you have to calculate the volume of the tracks you want affected by the RVA system. To do this, use the Calculate volume option in the Music Store found in the right-click popup menus of Stores, Artists, Records and Tracks. When you activate this option, a small window will pop up with a progress bar. You can move this window out of your way, and proceed with using Aqualung. Processing will be carried out in the background, and should not affect your ability to play music at all. Calculated volume levels will be saved and restored with the rest of the Music Store. The values are shown in the Edit track dialog.

When you are done with this, open the Settings dialog (right-click almost anywhere in the main window), and select the Playback RVA notebook page.

If Enable playback RVA is unchecked, the whole RVA system is turned off. No tracks receive adjustment. If playback RVA is enabled, you can select a listening environment that matches your setup. The idea is that the better your environment, the smaller adjustment you need to enjoy the music. If you work in a noisy workshop (and listen to Aqualung-played music) then it is best to minimize the volume differences between tracks so all tracks will be uniformly audible at a particular volume setting. If you can afford to listen to music in a silent room with high quality headphones or good near-field monitors, you should choose Audiophile which will yield no change to volumes.

The diagram shows the input/output transfer function applied to the previously measured track loudness to obtain the adjustment needed for a particular track. The diagram is 24 dB large in both directions, with the (0, 0) point being in the upper right corner. The blue line shows the identity function (no change), while the red line shows the output volume (the actual transfer function). The adjustment applied at a particular track volume is the vertical distance between the two lines at that position. The transfer function is linear. You can use the Reference volume and Steepness controls to change its position.

In most cases, it is desirable that tracks of the same record receive the same adjustment, so as to preserve the volume differences internal to the record. This can be enabled by checking Apply averaged RVA to tracks of the same record. When enabled, volume levels of the same record will be averaged and all tracks will be adjusted by an average value. Please note that measured volume levels are converted to RVA values when you add something from the Music Store to the Playlist. Therefore, this feature works only when you add an Artist or a Record. If you add a record by adding all the Tracks manually one after another, they will all receive independent RVA values. Also, changing RVA settings will not affect entries already in the Playlist.

There are many records having one or two tracks that really stand out of the average volume level. (For example, there is one very silent track on an otherwise loud record.) In this case, these tracks would pull down the average volume. To get around this, you can adjust a threshold that will be used to sort out tracks that stand out too much and will be disregarded when computing the average volume.

You can select whether you want to specify a threshold in linear volume units [dBFS] or you want to specify a percentage of the standard deviation of the set of individual track volumes to use as a threshold. The default values should work well for the vast majority of records. If you always want every track's volume to count in the average adjustment of the record, choose the linear threshold and set it to a really big value (say, 30 dB) so all tracks will be within this range.

For external tracks added to the Playlist and having no volume information, you can specify a fixed RVA value using RVA for Unmeasured Files. This applies to all tracks coming from outside the Music Store or a native XML playlist file, and to URLs.

You also have the possibility to always use a manually specified, fixed value as RVA for a particular track. In the Edit track dialog for that track, check the Use manual RVA value checkbox and set the value with the spinbutton on its right. If you e.g. import an ID3v2.4 RVA tag from an MP3 file, it will also set this field thereby circumventing Aqualung's own RVA calculation.

It is possible to have more volume calculations in progress at a time. If you need to measure a few records, you don't have to wait for the previous one to finish. RVA calculations can also be paused, so should you suddenly need the whole CPU capacity, you don't have to abort the process – just pause it, and resume when things go down.