Datasheet

3−14
CAUTION: No soft transition is implemented when changing bass and treble filter sets;
soft transitions only apply when adjusting gains (shelves) within a given filter set. The
variable TBLC should be set so that the dwell time at each shelf is never less than 32
audio sample periods; otherwise, audio artifacts could be introduced into the audio data
stream. It is recommended that these registers be written before the bass/treble bypass
values (subaddresses 0x73, 0x74, and 0x75) are set to pass audio through the
bass/treble filters.
Figure 3−13 summarizes the bass and treble adjustments available within each monaural channel. As noted in
Figure 3−13, the 3-dB frequency for the bass filter sets decreases in value as the filter set number is increased,
whereas the 3-dB frequency for the treble filter set increases in value as the filter set number is increased. The valid
selection for bass and treble sets ranges from 1 to 5.
Table 3−2 and Table 3−3 list, respectively, the bass and treble filter shelf selections for all 1/2-dB settings between
18-dB cut and 18-dB boost. The treble and bass selections are not the same, and the delta in the selection values
between 1/2-dB points is not constant across the 36-dB range. Table 3−2 and Table 3−3 do not list all 150 filter shelf
selections, but all 150 selection values for both bass and treble are valid, allowing the use of linear potentiometer or
GUI-based sliders. Table 3−2 and Table 3−3 are provided for those applications requiring the adjustment of bass and
treble in 1/2-dB steps.
CAUTION: Filter set selections 6 and 7 are reserved. Filter shelf selections 0 and 151
through 255 are reserved. Programming a reserved value could result in erratic and
erroneous behavior.
As an example, consider the case of a 44.1-kHz audio sample rate. For this audio rate it is desired to have, for all
three monaural channels
• A 3-dB bass shelf corner frequency of 100 Hz
• A bass shelf volume boost of 9 dB
• A 3-dB treble shelf corner frequency of 8.1 kHz
• A treble shelf volume cut of 4 dB
Bass and treble filter set selections can be made by referring to Figure 3−13. For a 44.1-kHz audio sample rate, filter
set 5 provides a 3-dB bass corner frequency at 115 Hz, and filter set 3 provides a 3-dB treble corner frequency at
8.269 kHz. These corner frequencies are the closest realizable corner frequencies to the specified 100-Hz bass and
8.1-kHz treble corner frequencies.
Table 3−2 provides the indices for achieving specified bass volume levels. An index of 0x55 yields a bass shelf gain
of 9 dB, which matches the specified shelf volume boost of 9 dB. Table 3−3 provides the indices for achieving specified
treble volume levels. An index of 0x7A yields a treble shelf cut of 4 dB (−4-dB gain), which matches the specified shelf
volume cut of 4 dB.
Figure 3−14 presents the resulting subaddress entries required to implement the parameters specified in the bass
and treble example.