TDA7439_08 Datasheet, PDF (8/23 Pages) STMicroelectronics – Three-band digitally-controlled audio processor

Application suggestions
3
Application suggestions
TDA7439
The first and the last stages are volume control blocks. The control range is 0 to -47 dB and
mute for the first stage and 0 to -79 dB and mute for the last one. Both control blocks have a
step resolution of 1 dB.
This very high resolution allows the implementation of systems free from any noisy
acoustical effect.
The TDA7439 audio processor provides 3 bands of tone control (bass, mid-range and
treble).
3.1
3.1.1
Tone control
Bass, mid-range stages
The bass and the mid-range cells have the same structure.
However, the bass cell has an internal resistor R_B of typically 44 kΩ whilst the mid-range cell
has an internal resistor R_M of typically 25 kΩ.
Several filter types can be implemented by connecting external components to the bass/mid
IN and OUT pins.
Typical responses are shown in Figure 8, Figure 9 and Figure 11.
Figure 4. Bass/mid-range filter implementation
Ri internal
IN
OUT
C₁
C₂
R₂
D95AU313
Figure 4. refers to the basic T-type band-pass filter. Starting from the filter component values
(R1 (internal) and R2, C1, C2 (external)) then the centre frequency f_C, the gain Av at
maximum boost and the filter Q factor are computed as follows:
fC
=
--------------------------------¹--------------------------------
2 ⋅ π ⋅ R1 ⋅ R2 ⋅ C1 ⋅ C2
A_V = ^R-----²----^C--_R---²--₂--+-_C----^R-₁----²-+---^C--_R--¹--₂---+-_C----^R-₂----ⁱ-^C-----¹--
Q = -----^R-_R---¹--₂---_C^â‹---^R--₁---²--+---^â‹--_R-^C---₂-¹---_C--^â‹---_2C-----²--
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