DIGITAL AUDIO PROCESSING FOR PLAYBACK
H(z) +
N0 ) N1 z
*1
32768 * D1 z
*1
(2)
ǒ
N0 ) 2 N1 z
*1
) N2 z
*2
32768 * 2 D1 z
*1
* D2 z
*2
Ǔǒ
N3 ) 2 N4 z
*1
) N5 z
*2
32768 * 2 D4 z
*1
* D5 z
*2
Ǔ
(3)
TLV320AIC34
SLAS538A – OCTOBER 2007 – REVISED NOVEMBER 2007
The DAC channel consists of optional filters for de-emphasis and bass, treble, midrange level adjustment,
speaker equalization, and 3-D effects processing. The de-emphasis function is implemented by a programmable
digital filter block with fully programmable coefficients (see page 1, registers 21 – 26 for left channel, page 1,
registers 47 – 52 for right channel). If de-emphasis is not required in a particular application, this programmable
filter block can be used for some other purpose. The de-emphasis filter transfer function is given by:
where the N0, N1, and D1 coefficients are fully programmable individually for each channel. The coefficients that
should be loaded to implement standard de-emphasis filters are given in Table 4 .
Table 4. De-Emphasis Coefficients for Common Audio Sampling Rates
SAMPLING FREQUENCY (kHz) N0 N1 D1
32 16,950 – 1,220 17,037
44.1 15,091 – 2,877 20,555
48 14,677 – 3,283 21,374
In addition to the de-emphasis filter block, the DAC digital effects processing includes a fourth-order digital IIR
filter with programmable coefficients (one set per channel). This filter is implemented as a cascade of two biquad
sections with frequency response given by:
The N and D coefficients are fully programmable, and the entire filter can be enabled or bypassed. The structure
of the filtering when configured for independent channel processing is shown in Figure 28 , with LB1
corresponding to the first left-channel biquad filter using coefficients N0, N1, N2, D1, and D2. LB2 similarly
corresponds to the second left-channel biquad filter using coefficients N3, N4, N5, D4, and D5. The RB1 and
RB2 filters refer to the first and second right-channel biquad filters, respectively.
Figure 28. Structure of the Digital Effects Processing for Independent Channel Processing
The coefficients for this filter implement a variety of sound effects, with bass boost or treble boost being the most
commonly used in portable audio applications. The default N and D coefficients in the part are given in Table 5
and implement a shelving filter with 0-dB gain from dc to approximately 150 Hz, at which point it rolls off to a
3-dB attenuation for higher-frequency signals, thus giving a 3-dB boost to signals below 150 Hz. The N and D
coefficients are represented by 16-bit, 2s-complement numbers with values ranging from – 32,768 to 32,767.
38 Submit Documentation Feedback Copyright © 2007, Texas Instruments Incorporated
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