1 The TLV320AIC3X is a powerful four channel low power audio codec family.
2 More information is available at:
3 http://focus.ti.com/docs/prod/folders/print/tlv320aic34.html
5 http://www.ti.com/lit/gpn/tlv320aic34
7 The codec driver leverages the codecs effects through alsa controls and a
8 hwdep device for controlling the hardware fourth-order IIR filter block.
10 There's an alsa control, "3D Control - Depth" for depth simulation.
11 The rest of the controls are for the IIR filter:
13 1- A control for setting the bass/treble gain, which sets the filter's
14 coefficients to certain precalculated values.
15 2- A control for 'off' / 'on' / 'external control'. 'On' means the
16 bass/treble gain is used, while 'external control' means the
17 coefficients have been set through the hwdep device (see below).
21 The IIR Filter consists of 2 cascaded biquads. The formula is:
23 | (N0 + 2*N1*z^-1 + N2*z^-2) || (N3 + 2*N4*z^-1 + N5*z^-2) |
24 | ------------------------------ || ------------------------------ |
25 \ (32768 - 2*D1*z^-1 - D2*z^-2) / \ (32768 - 2*D4*z^-1 - D5*z^-2) /
27 The filter can be controlled through an alsa hwdep device, via
28 libalsa. A short example follows, note that the data struct must be
29 passed *EXACTLY* as shown:
32 #include <alsa/hwdep.h>
34 struct _iirfilter_data {
35 int16_t N0, N1, N2, D1, D2;
36 int16_t N3, N4, N5, D4, D5;
42 snd_hwdep_open(&hwdep, "IIR Filter", "w");
46 .N0 = 27619, .N1 = -27034, .N2 = 26461, .D1 = 32131, .D2 = -31506,
47 .N3 = 27619, .N4 = -27034, .N5 = 26461, .D4 = 32131, .D5 = -31506
50 snd_hwdep_write(hwdep, (void*)iirfilter_data, sizeof(iirfilter_data));
53 snd_hwdep_read(hwdep, (void*)iirfilter_data, sizeof(iirfilter_data));
55 /* To enable/disable filtering: */
56 int arg = 1; /* 1 = enable, 0 = disable */
57 snd_hwdep_ioctl(hwdep, 1, &arg);