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Auto Volume (Recorder only)
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. That time
interval is configurable here. Short values like 20ms 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 less sharp
changes in volume level.
Super Bass (Recorder Only)
This setting boosts the volume of bass frequencies, making the sound of drums and
bass guitar louder in comparison to the rest of the track. This setting only has an
effect if Loudness is set to a value larger than 0dB.
MDB - Micronas Dynamic Bass (Recorder Only)
The rest of the parameters on this menu relate to the Micronas Dynamic Bass
(MDB) function. This 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 in believing it's hearing tones that the headphones or speakers
aren't capable of reproducing. Try it and see what you think.
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 the 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 time 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 off, 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.
30 Rockbox User Manual