8.5.2.5 Dynamic Parametric Equalizer (DPEQ)

The dynamic parametric equalizer mixes the audio signals routed through two paths containing one BQ each based upon the signal level detected by the sense path, as shown in Figure 45. The sense path contains one BQ, which can be used to focus the DPEQ sensing on a specific frequency bandwidth. An alpha filter structure is used to sense the energy in the sense path and setting the dynamic mixing ratios.

Figure 45. DPEQ Signal Path

The dynamic mixing is controlled by offset, gain, and alpha coefficients in a 1.31 format. The alpha coefficient controls the average time constant in ms of the signal data in the sense path. The offset and gain coefficients control the dynamic mixing thresholds shown in Figure 46.

Figure 46. Dynamic Mixing

The offset, gain and alpha coefficients are calculated as follows:

Equation 10.

Equation 11.

where

• T2 ≥ –20 dB

Equation 12.

where

• T2 < –20 dB

Equation 13.

Equation 14.

Equation 15.

where

• T1 and T2 are in dB
• The time constant is in ms

The DPEQ control coefficients are located in book 0x8C, page0x20. Register 0x44 is alpha coefficient, register 0x48 is gain coefficient and register 0x4C is offset coefficient.

The high level path BQ, low level path BQ, and sense path BQ coefficients use a 1.31 format as shown in Table 29. The DPEQ BQs don't have a gain scale to compensate for any BQ gain reduction due to the requirements of the 1.31 format. During tuning, the reduced gain can be compensated by using the BQ gain scale or the DRC offset coefficient.

The DPEQ sense gain scale is located in the sensing path. The DPEQ sense gain scale can be used to shift the dynamic mixing thresholds by changing the signal level in the sensing path. A positive dB gain shifts the dynamic mixing thresholds down by the gain amount and a negative dB gain shifts the dynamic mixing thresholds up by the gain amount.