Operation Manual

Chapter 6. Sound Settings 51

6.9. Dithering

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 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 sig-

nal. 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.

6.10. Timestretch

Enabling Timestretch allows you to change the playback speed without it aﬀecting

the pitch of the recording. After enabling this feature and rebooting, you can access

this via the Pitch Screen. This function is intended for speech playback and may

signiﬁcantly dilute your listening experience with more complex audio. See section 4.3.3

(page 34) for more details about how to use the feature.

6.11. Compressor

The Compressor reduces, or compresses, the dynamic range of the audio signal. This

makes the quieter and louder sections closer to the same volume level by progressively

reducing the gain of louder signals. When subsequently ampliﬁed, this has the eﬀect of

making the quieter sections louder while keeping the louder sections from clipping. This

allows listening to the quiet sections of dynamic material in noisy environments while

preventing sudden loud sections from being overbearing.

There are several settings associated with the compressor. The ﬁrst, and most impor-

tant, is the Threshold. The threshold is the audio input level at which the compressor

begins to act. Any level louder than the threshold will be compressed to some extent.

The maximum amount of compression, or the quietest level at which the compressor will

operate, is -24 dB. The default of Oﬀ disables the compressor.

The Makeup Gain setting has two options: Oﬀ and Auto. Oﬀ means that the

compressed audio will not be ampliﬁed after compression. The default of Auto will

The Rockbox manual (version 3.10) Packard Bell Vibe 500