LM4947

C3DR

C3DL

C3DL

C3DR

(internal resistors)

LM4947, LM4947TLEVAL

SNAS349D – JUNE 2006 – REVISED MAY 2013

www.ti.com

Table 5. Output Volume Control Table (continued)

Volume Step

xVC4

xVC3

xVC2

xVC1

xVC0

Gain, dB

25

1

1

0

0

0

7.50

26

1

1

0

0

1

9.00

27

1

1

0

1

0

10.50

28

1

1

0

1

1

12.00

29

1

1

1

0

0

13.50

30

1

1

1

0

1

15.00

31

1

1

1

1

0

16.50

32

1

1

1

1

1

18.00

Table 6. Output Mode Selection

Output Mode

MC2

MC1

MC0

Handsfree Mono Output

Right HP Output

Left HP Output

Number

0

0

0

0

SD

SD

SD

1

0

0

1

2 x GM x M

MUTE

MUTE

2

0

1

0

SD

GM x M

GM x M

3

0

1

1

GL x L + GR x R

MUTE

MUTE

4

1

0

0

SD

GR x R

GL x L

5

1

0

1

GL x L + GR x R + 2(GM x M)

MUTE

MUTE

6

1

1

0

SD

GR x R + GM x M

GL x L + GM x M

7

1

1

1

GR x R + GL x L

GR x R

GL x L

TI 3D ENHANCEMENT

The LM4947 features a stereo headphone, 3D audio enhancement effect that widens the perceived soundstage

from a stereo audio signal. The 3D audio enhancement creates a perceived spatial effect optimized for stereo

headphone listening. The LM4947 can be programmed for a “narrow” or “wide” soundstage perception. The

narrow soundstage has a more focused approaching sound direction, while the wide soundstage has a spatial,

theater-like effect. Within each of these two modes, four discrete levels of 3D effect that can be programmed:

low, medium, high, and maximum (Table 2), each level with an ever increasing aural effect, respectively. The

difference between each level is 3dB.

The external capacitors, shown in Figure 88, are required to enable the 3D effect. The value of the capacitors set

the cutoff frequency of the 3D effect, as shown by Equation 1 and Equation 2. Note that the internal 20k

Ω

resistor is nominal (±25%).

Figure 88. External 3D Effect Capacitors

f3DL(-3dB) = 1 / 2π * 20kΩ * C3DL

(1)

f3DR(-3dB) = 1 / 2π * 20kΩ * C3DR

(2)

Optional resistors R3DL and R3DR can also be added (Figure 89) to affect the -3dB frequency and 3D magnitude.

26

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