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6  Sound Settings


PIC

Figure 6.1.: The sound settings screen

The sound settings menu offers a selection of sound settings you may change to customise your listening experience.

6.1 Volume
6.2 Bass
6.3 Volume Limit
6.4 Treble
6.5 Balance
6.6 Channels
6.7 Stereo Width
6.8 Loudness
6.9 Auto Volume
6.10 Super Bass
6.11 MDB – Micronas Dynamic Bass

6.1  Volume

This setting adjusts the volume of your music. Like most professional audio gear and many consumer audio products, Rockbox uses a decibel scale where 0 dB is a reference that indicates the maximum volume that the player can produce without possible distortion (clipping). All values lower than this reference will be negative and yield a progressively softer volume. Values higher than 0 dB are available and can be used to raise the volume more than would otherwise be possible. These volume levels will ordinarily lead to distorted sound, but might work nicely for music that has an otherwise low volume level. The volume can be adjusted from a minimum of -100 dB to a maximum of +12 dB.

6.2  Bass

This setting emphasises or suppresses the lower (bass) frequencies in the sound. A value of 0 dB means that bass sounds are unaltered (flat response). The minimum setting is -12 dB and the maximum is 12 dB.

6.3  Volume Limit

This setting adjusts the maximum volume of your music. The setting is by default set to the maximum volume which equals to no limit. To set a volume limit, select a volume from the list and the maximum volume will be limited to the selected value all over the system.

6.4  Treble

This setting emphasises or suppresses the higher (treble) frequencies in the sound. A value of 0 dB means that treble sounds are unaltered (flat response). The minimum setting is -12 dB and the maximum is 12 dB.

6.5  Balance

This setting controls the balance between the left and right channels. The default, 0, means that the left and right outputs are equal in volume. Negative numbers increase the volume of the left channel relative to the right, positive numbers increase the volume of the right channel relative to the left.

6.6  Channels

A stereo audio signal consists of two channels, left and right. The Channels setting determines if these channels are to be combined in any way, and if so, in what manner they will be combined. Available options are:

Stereo.
Leave the audio signal unmodified.
Mono.
Combine both channels and send the resulting signal to both stereo channels, resulting in a monophonic output.
Custom.
Allows you to manually specify a stereo width with the Stereo Width setting described later in this chapter.
Mono Left.
Plays the left channel in both stereo channels.
Mono Right.
Plays the right channel in both stereo channels.
Karaoke.
Removes all sound that is common to both channels. Since most music is recorded with vocals being equally present in both channels to make the singer sound centrally placed, this often (but not always) has the effect of removing the voice track from a song. This setting also very often has other undesirable effects on the sound.

6.7  Stereo Width

Stereo width allows you to manually specify the effect that is applied when the Channels setting is set to “custom”. All values below 100% will progressively mix the contents of one channel into the other. This has the effect of gradually centering the stereo image, until you have monophonic sound at 0%. Values above 100% will progressively remove components in one channel that is also present in the other. This has the effect of widening the stereo field. A value of 100% will leave the stereo field unaltered.

6.8  Loudness

When listening at low volumes, the ear will tend to make bass and treble frequencies sound quieter than they really are. To compensate for this, Loudness is an effect which emphasises bass and treble in a fashion suited to the human ear. Frequencies in the vocal range are unaffected, since the human ear picks these up very easily at any sound level. It is of course also possible to use this effect at higher volumes for enhanced bass and treble.

6.9  Auto Volume

Auto volume is a feature that automatically lowers the volume on loud parts, and then slowly restores the volume to the previous level over a time interval. This setting allows this time interval to be configured. Short values like 20 ms are useful for ensuring a constant volume for in-car use and other applications where background noise makes a constant loudness desirable. A longer timeout means that the change in volume back to the previous level will be smoother, so there will be fewer sharp changes in volume level.

6.10  Super Bass

This setting changes the threshold at which bass frequencies are affected by the Loudness setting, making the sound of drums and bass guitar louder in comparison to the rest of the sound. This setting only has an effect if Loudness is set to a value larger than 0 dB.

6.11  MDB – Micronas Dynamic Bass

The rest of the parameters in this menu relate to the Micronas Dynamic Bass (MDB) function. MDB is designed to enable the user to hear bass notes that the headphones and/or speakers are not capable of reproducing. Every tone has a fundamental frequency (the “main tone”) and also several harmonics, which are related to that tone. The human brain has a mechanism whereby it can actually infer the presence of bass notes from the higher harmonics that they would generate.

The practical upshot of this is that MDB produces a more authentic sounding bass by tricking the brain into believing it is hearing tones that the headphones or speakers are not capable of reproducing.

The MDB parameters are as follows:

MDB enable.
This turns the MDB feature on or off. For many users this will be the only setting they need, since Rockbox picks sensible defaults for the other parameters. MDB is turned off by default.
MDB strength.
How loud the harmonics generated by MDB will be.
MDB Harmonics.
The percentage of the low notes that is converted into harmonics. If low notes are causing speaker distortion, this can be set to 100% to eliminate the fundamental completely and only produce harmonics in the signal. If set to 0% this is the same as turning the MDB feature off.
MDB Centre Frequency.
The cutoff frequency of your headphones or speakers. This is usually given in the specification for the headphones/speakers.
MDB shape.
It is recommended that this parameter be set to 1.5 times the centre frequency.

This is the frequency up to which harmonics are generated. Some of the lower fundamentals near the cut-off range will have their lower harmonics cut, since they will be below the range of the speakers. Fundamentals between the cut-off frequency and the lower frequency will have their harmonics proportionally boosted to compensate and restore the ‘loudness’ of these notes.

For most users, the defaults should provide an improvement in sound quality and can be safely left as they are. For reference, the defaults Rockbox uses are:


Setting

Value


MDB Strength

50 dB

MDB Harmonics

48%

MDB Centre Frequency

60 Hz

MDB Shape

90 Hz