How to tweak the MDB settings

Introduction to MDB

The Micronas Dynamic Bass is a feature in the MAS3587F that can improve the sound by adding (simulated) bass.

(Note: This was called Bass boost in earlier versions of Rockbox, with only the Strength parameter configurable)

Most headphones and speakers are unable to reproduce the low bass frequencies. However, one can fool the human brain into thinking that the low frequencies really are there.

(From the MAS3587 data sheet, page 10):

In addition to dynamically amplifying the low frequency bass signals, the MDB exploits the psychoacoustic phenomenon of the ‘missing fundamental’. Adding harmonics of the frequency components below the cutoff frequency gives the impression of actually hearing the low frequency fundamental, while at the same time retaining the loudness of the original signal.

The MDB parameters

MDB Enable

This one simply enables or disables the effect.

MDB Strength

This sets the strength of the effect. Range 0-127dB according the the data sheet.

MDB Harmonics

This tells the MAS how to mix the original signal and the generated harmonics. There may be occasions were you only want the harmonics, because the loudspeaker distorts the original low frequencies.

MDB Center frequency

This tells the MAS the cutoff frequency of your headphones/speakers. The frequencies below this will have harmonics generated.

MDB Shape

This tells the MAS the frequency range for which to add harmonics. The narrower the range, the "harder" bass sound you will get. The data sheet recommends this to be approx. 1.5 times the center frequency. (note: maybe an Auto setting could be nice?)

Rockbox defaults

Setting	Value
MDB Enable	No
MDB Strength	50dB
MDB Harmonics	48%
MDB Center frequency	60Hz
MDB Shape	90Hz

You can read more about Micronas Dynamic Bass in the MAS3587 data sheet, pages 10, 44 and 46.