TAS3103DBT datasheet(73/146 Pages) TI

73 / 146 page

3−13

CAUTION: There is no soft transition 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.

Figure 3−12 summarizes the bass and treble adjustments available within each monaural channel. As noted in

Figure 3−12, 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 are 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 illegal. Filter shelf selections 0 and 151

through 255 are illegal. Programming an illegal 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 3−12. 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 3−13 presents the resulting subaddress entries required to implement the parameters specified in the bass

and treble example.

TAS3103DBT Datasheet(PDF) 73 Page - Texas Instruments