Figure 6.1: The sound settings screen
The Sound Settings menu offers a selection of sound properties you may change to customise your listening experience.
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. The volume can be adjusted from a minimum of -74 dB to a maximum of +6 db.
add platform specific information here
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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.
A stereo audio signal consists of two channels, left and right. The Channels setting controls if these channels are to be combined in any way, and if so, in what manner they will be combined. Available options are:
| Setting | Description |
| 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 the same in 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. |
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.
Crossfeed attempts to make the experience of listening to music on headphones more similar to listening to music with stereo speakers. When you listen to music through speakers, each ear will hear sound originating from both speakers. However, the sound from the left speaker reaches your right ear slightly later than it does your left ear, and vice versa.
The human ear and brain together are very good at interpreting the timing differences between direct sounds and reflected sounds and using that information to identify the direction that the sound is coming from. On the other hand, when listening to headphones, each ear hears only the stereo channel corresponding to it. The left ear hears only the left channel and the right ear hears only the right channel. The result is that sound from headphones does not provide the same spatial cues to your ear and brain as speakers, and might for that reason sound unnatural to some listeners.
The crossfeed function uses an algorithm to feed a delayed and filtered portion of the signal from the right channel into the left channel and vice versa in order to simulate the spatial cues that the ear and brain receive when listening to a set of loudspeakers placed in front of the listener. The result is a more natural stereo image that can be especially appreciated in older rock and jazz records, where one instrument is often hard-panned to just one of the speakers. Many people will find such records tiring to listen to using earphones and no crossfeed effect.
Crossfeed has the following settings.
Most users will find the default settings to yield satisfactory results, but for the more adventurous user the settings can be fine-tuned to provide a virtual speaker placement suited to ones preference.
Beware that the crossfeed function is capable of making the audio distort if you choose settings which result in a too high output level.
Rockbox features a parametric equalizer. As the name suggests, a parametric equalizer lets you control several different parameters for each band of the equalizer. Rockbox’s parametric EQ is composed of five different EQ bands:
| EQ Band(s) | Description |
| Band 0: Low shelf filter | A low shelf filter boosts or lowers all frequencies below the designated cutoff point. The “bass”control on most home or car stereos is an example of a low shelf filter. The low shelf filter in Rockbox is more flexible than a simple “bass” control, because a simple bass control only lets you adjust the amount of gain that is applied. Rockbox lets you control the amount of gain that is applied (i.e., the amount that the bass is boosted or cut) too, but Rockbox also allows you to adjust the “cutoff” frequency where the shelving starts to take effect. For example, a cutoff frequency of 50 Hz will adjust only very low frequencies. A cutoff frequency of 200 Hz, on the other hand, will adjust a much wider range of bass frequencies. |
| Bands 1-3: Peaking filters | Peaking EQ filters boost or low a center frequency that you select, as well as the frequencies within a certain distance of that center. Graphic equalizers in home stereos are usually peaking filters. The peaking EQs on Rockbox’s parametric equalizer let you adjust three different parameters for each EQ band 1 through 3. The “center” parameter controls the center frequency that is adjusted by that EQ band. The “gain” parameter controls how much each band is adjusted. Positive numbers make the EQ band louder, while negative numbers make that EQ band quieter. Finally, the “Q” parameter controls how wide or narrow each EQ band is. Higher Q values will affect a narrow band of frequencies, while lower Q values will affect a wider band of frequencies. |
| Band 4: Hi shelf filter | A high shelf filter boosts or lowers all frequencies above a designated cutoff point. The “treble” control on most home or car stereos is an example of a high shelf filter. The high shelf filter is adjusted the same way as the low shelf filter, except that it works on the high end of the frequency spectrum rather than the low end. |
So, as a general guide, EQ band 0 should be used for lows, EQ bands 1 through 3 should be used for mids, and EQ band 4 should be used for highs.
| Key | Action |
| Scroll Up | Raises the highlighted parameter. |
| Scroll Down | Lowers the highlighted parameter. |
| Play | Moves to the previous EQ band. |
| Submenu | Moves to the next EQ band. |
| Select | Toggles the cursor among the three parameters (gain, center frequency, Q) for the selected EQ band. |
| Power/Right | Exits the graphic EQ screen. |
If your music distorts when using the EQ, trying changing this setting to a negative value.
This setting controls the dithering and noise shaping functionality of Rockbox.
Most of Rockbox’ audio file decoders work at a higher bit depth than the 16 bits used for output on the player’s audio connectors. The simplest way in which to convert from one bit depth to another is simply discarding all the surplus bits. This is the default behaviour, and adds distortion to the signal that will vary in character along with the desired sound.
Dithering adds low-level noise to the signal prior to throwing away the surplus bits, which gives the resulting signal a uniform noise floor which is independent of the signal. Most people find this noise preferable to the time-varying noise heard when not performing dithering.
After dithering, noise shaping is performed. This basically just pushes the dithering noise to the parts of the frequency spectrum humans cannot hear so easily. In Rockbox’ case, some of the noise is pushed up to above 10 kHz.
This setting will be put to its best use when listening to dynamic music with frequently occuring quiet parts, classical music being a typical example. It is worth noting that the effects of dithering and noise shaping are very subtle, and not easily noticable.
Rockbox uses highpass triangular distribution noise as the dithering noise source, and a third order noise shaper.
