Dithering - IRiver H320 Manual

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HAPTER OUND

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 fre-
quently 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.
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