Why is 44.1 kHz sampling in CD or digital music file (mp3 or wma, ...)?

Currently famous digital music file use 44.1 kHz sampling rate.

As you know, 

- Normal human being can hear 20 Hz ~ 20,000 Hz sound.

- And from the Nyquist sampling theorem, 

---------------------------------------------------------------------

 The Nyquist sampling theorem provides a prescription for the nominal sampling interval required to avoid aliasing. It may be stated simply as follows:

 The sampling frequency should be at least twice the highest frequency contained in the signal.Or in mathematical terms:

     fs >= 2 * fc

(http://redwood.berkeley.edu/bruno/npb261/aliasing.pdf)

In this reason, in the digital music need only 40 kHz sampling rate.

Why is 44.1 kHz sampling rate used in the world?
It is based on Video Tape,
1. http://www.cs.columbia.edu/~hgs/audio/44.1.html
2.http://en.wikipedia.org/wiki/44,100_Hz 

Kconfig: help or ---help--- ?

From the http://kernel.org/doc/Documentation/kbuild/kconfig-language.txt

- help text: "help" or "---help---"   This defines a help text. The end of the help text is determined by   the indentation level, this means it ends at the first line which has   a smaller indentation than the first line of the help text.   "---help---" and "help" do not differ in behaviour, "---help---" is   used to help visually separate configuration logic from help within   the file as an aid to developers.

Android - Hotplug Off (Multi-Core enable)

If your device has root permission

adb shell stop mpdecision

adb shell "echo 1 > /sys/devices/system/cpu/cpu1/online"

or

# stop mpdecision

# echo 1 > /sys/devices/system/cpu/cpu1/online

# ...

xda - developers

http://forum.xda-developers.com/showthread.php?t=1216197

update 1/31

Support for hot-pluggable CPUs

CONFIG_HOTPLUG_CPU=y

or # CONFIG_HOTPLUG_CPU is not set

http://cateee.net/lkddb/web-lkddb/HOTPLUG_CPU.html

Enable bootchart in the Android

In the Android source code

STEP 1. ----------

In the device side

1. enable bootchart flag

$ export INIT_BOOTCHART=true

2. and build the Android source code

3. After flashing binary

$ adb shell

$ mkdir /data/bootchart

$ echo 60 > /data/bootchart-start

(It means that bootchart log will be saved until 60 seconds)

$ exit

(exit adb)

4. reboot device

$ adb reboot

You can find some log files in the /data/bootchart/ directory

Tip.

- You can find "bootchart.c & bootchart.h" under the ../init/ directory.

- In the same directory there is a Android.mk file.

INIT_BOOTCHART is used in this make file.

STEP 2. ----------

In the linux system side

install bootchart

$ sudo apt-get install bootchart

STEP 3. ----------

after getting bootchart log files

1. copy log files from the Android device to Linux system

$ adb push /data/bootchart/.

2. compress the all log files

$ tar -czf bootchart.tgt *

3. run bootchart

$ bootchart bootchart.tgz

$ ls

bootchart.png bootchart.tgz

* If you meet the error message,

" ZeroDivisionError: flat division by zero"

Please refer to below site: Error while extracting bootchart.tgz and patch the script files.