Added de-emphasis filter functions and speaker protection.

[aic34-eq] / kernel-2.6.28 / Documentation / sound / alsa / soc / tlv320aic3x.txt

diff --git a/kernel-2.6.28/Documentation/sound/alsa/soc/tlv320aic3x.txt b/kernel-2.6.28/Documentation/sound/alsa/soc/tlv320aic3x.txt
index c82cb3b..71dd24d 100644 (file)
--- a/kernel-2.6.28/Documentation/sound/alsa/soc/tlv320aic3x.txt
+++ b/kernel-2.6.28/Documentation/sound/alsa/soc/tlv320aic3x.txt
@@ -1,6 +1,3 @@
-WARNING: THINGS DESCRIBED BELOW ARE NOT YET IN THE REPOS. THEY WILL BE, 
-VERY SOON.
-
 The TLV320AIC3X is a powerful four channel low power audio codec family.
 More information is available at:
     http://focus.ti.com/docs/prod/folders/print/tlv320aic34.html
@@ -15,18 +12,26 @@ The rest of the controls are for the IIR filter:
 
 1- A control for setting the bass/treble gain, which sets the filter's
    coefficients to certain precalculated values.
-2- A control for 'off' / 'on' / 'external control'. 'On' means the 
-   bass/treble gain is used, while 'external control' means the 
+2- A control for 'off' / 'Bass/Treble' / 'Custom'. 'Bass/Treble' means
+   the bass/treble gain controls are used, while 'custom' means the 
    coefficients have been set through the hwdep device (see below).
+Note: bass/treble controls are not yet implemented
 
+Filters
+--------
+Note: Setting a filter's coeffs automatically turns it off, it needs to
+be turned on explicitly.
 
+The De-emphasis filter can only be controlled on the machine driver level.
+For example for the n900 (rx51.c) it is used as highpass filter for
+speaker protection. See tlv320aic3x.h, aic3x_deemph_set_* for details.
 
 The IIR Filter consists of 2 cascaded biquads. The formula is:
  /                                \  /                                \
 |    (N0 + 2*N1*z^-1 + N2*z^-2)    ||    (N3 + 2*N4*z^-1 + N5*z^-2)    |
 |  ------------------------------  ||  ------------------------------  |
 |  (32768 - 2*D1*z^-1 - D2*z^-2)   ||   (32768 - 2*D4*z^-1 - D5*z^-2)  |
-\                                 /  \                                /
+ \                                /  \                                /
 
 The filter can be controlled through an alsa hwdep device, via 
 libasound. A short example follows, note that the data struct must be
@@ -71,5 +76,3 @@ int main() {
 }
 ------------------------------------------------------------------------
 
-
-