ZHCSGM5A August 2017 – November 2017 TLV320AIC3109-Q1
PRODUCTION DATA.
The DAC channel consists of optional filters for de-emphasis and bass, treble, midrange level adjustment, and speaker equalization. The de-emphasis function is implemented by a programmable digital filter block with fully programmable coefficients (see registers 21–26, page 1). If de-emphasis is not required in a particular application, this programmable filter block can be used for some other purpose. Equation 4 gives the de-emphasis filter transfer function:
where
Table 3 lists the coefficients that must be loaded to implement standard de-emphasis filters.
SAMPLING FREQUENCY | N0 | N1 | D1 |
---|---|---|---|
32 kHz | 16,950 | –1,220 | 17,037 |
44.1 kHz | 15,091 | –2,877 | 20,555 |
48 kHz(1) | 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. This filter is implemented as a cascade of two biquad sections with the 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 channel processing is illustrated in Figure 19, with LB1 corresponding to the first biquad filter using coefficients N0, N1, N2, D1, and D2. LB2 similarly corresponds to the second biquad filter using coefficients N3, N4, N5, D4, and D5.
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 device are given in Table 4 and implement a shelving filter with 0-dB gain from dc to approximately 150 Hz, at which point the filter 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, 2's-complement numbers with values ranging from –32,768 to 32,767.
COEFFICIENTS | ||||
---|---|---|---|---|
N0 = N3 | D1 = D4 | N1 = N4 | D2 = D5 | N2 = N5 |
27,619 | 32,131 | –27,034 | –31,506 | 26,461 |
The digital effects filters are recommended to be disabled when the filter coefficients are being modified. When new coefficients are being written to the device over the control port, a filter using partially updated coefficients can possibly implement an unstable system and lead to oscillation or objectionable audio output. By disabling the filters, changing the coefficients, and then reenabling the filters, these types of effects can be entirely avoided.