SGTL5000XNAA3 Datasheet, PDF (39/84 Pages) Freescale Semiconductor, Inc – Low Power Stereo Codec with Headphone Amp

DATASHEET
SGTL5000
5.9.4.1. 7-Band Parametric EQ
The 7-band PEQ allows the designer to compensate for speaker response and to
provide the ability to filter out resonant frequencies caused by the physical system
design. The system designer can create custom EQ presets such Rock, Speech,
Classical etc that allows the users the flexibility in customizing their audio.
The 7-band PEQ is implemented using 7 cascaded second order IIR filters. All fil-
ters are implemented using programmable biquad filters. Figure 17 shows the trans-
fer function and Direct Form 1 of the five coefficient biquadratic filter.
H (z)
=
b₀ + b₁z ^−1 + b₂ z ^−2
1 + a₁z^−1 + a₂ z^−2
Direct Form1
X(z)
∑
b0
H(z)X(z)
z ^−1
z ^−1
b₁
z ^−1
-a1
z ^−1
b₂
-a₂
Figure 17. 5-Coefficient Biquad Filter and Transfer Function
If a band is enabled but is not being used (flat response), then a value of 0.5 should
be put in b₀ and all other coefficients should be set to 0.0. Please note that the coef-
ficients must be converted to hex values before writing to the registers. By default,
all the filters are loaded with coefficients to give a flat response.
In order to create EQ presets such as Rock, Speech, Classical etc, the coefficients
must be calculated, converted to 20-bit hex values and written to the registers. Note
that coefficients are sample-rate dependent and separate coefficients must be gen-
erated for different sample rates. Please contact Freescale for assistance with gen-
erating the coefficients.
SGTL5000 EA2 DS-0-3
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