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Kamis, 17 Maret 2011

Android 2.2

Jakarta - Sistem operasi Android 2.1 saja saat ini masih belum dinikmati oleh semua jajaran ponsel Android. Namun kini sang penerus, Android 2.2, sudah dirumorkan tinggal menunggu waktu untuk dipamerkan Google.

Menurut Taylor Wimberly, seorang pengamat dan juga pendiri dari situs AndroidandMe.com, Google saat ini tengah sibuk untuk melakukan pengujian dari OS teranyar mereka yang memiliki nama sandi 'Froyo' tersebut.

Taylor mengaku tidak asal menggulirkan rumor, namun berdasarkan hasil analisis dan laporan dari sumber yang bisa dipercaya. "Para ahli di Google selalu memberi kode nama untuk setiap OS mereka, seperti Eclair untuk Android 2.1, dan Froyo untuk Android 2.2," ujarnya, dikutip detikINET dari AndroidandMe.com, Jumat (23/4/2010).

Tentunya ada sejumlah peningkatan kemampuan dari Android versi baru yang tengah digodok tersebut. Menurut Taylor, Google coba untuk lebih fokus bagaimana meningkatkan performa dari OS-nya.

Beberapa fitur tambahan juga dikatakan bakal terbenam di Froyo, seperti JIT compiler, tambahan RAM, OpenGL ES 2.0, Flash 10.1 dan lainnya.

Bahkan, Taylor berani memprediksi bahwa Android 2.2 akan dipamerkan pada 19 Mei mendatang. Yakni ketika sang raksasa internet tersebut menyelenggarakan event Google I/O 2010.
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Kamis, 27 Januari 2011

Sony Ericsson Arc

he Sony Ericsson Xperia Arc is a forthcoming smartphone from Sony Ericsson.

Contents

 

 

 

DSC00042

 

Basics

The Xperia Arc operates on Android 2.3.

The display features a Sony Mobile BRAVIA® Engine which allows you to view crisp and clear pics and video in vivid colours on the 4.2” Reality display.

It also features an Exmor R™ sensor that lets you capture high-quality movies and stills in low lit areas, and then you can show them in stunning HD direct on your TV via the HDMI connector on the Sony Ericsson Xperia Arc.

Reception

The Xperia Arc was first revealed on January 5, 2011 at CES 2011.[1] It received praise for its features and design.

Specifications

Display

  • 4.2" touchscreen with a resolution of 854 × 480 pixels (FWVGA)
  • 16,777,216 color TFT display

Device colors

The phone is available in two colors

  • Midnight Blue
  • Misty Silver

Physical Attributes

Dimensions: 125.0 × 63.0 × 8.7 millimeters; 4.9 × 2.5 × 0.34 inches
Weight with battery: 117 grams; 4.1 ounces

Battery

Lithium-Polymer, 1500 mAh.

Talk time:
GSM: 7 h
HSDPA: 7 h

Stand by:
GSM: 400 - 430 h

Music Play: up to 31 h

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Selasa, 18 Januari 2011

android

Market android
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Senin, 17 Januari 2011

Android Market

Android Market is an online software store developed by Google for Android devices. An application program ("app") called "Market" is preinstalled on most Android devices and allows users to browse and download apps published by third-party developers, hosted on Android Market. The website, rather than the Market app itself, provides details of some of the available apps, in particular those that are termed "Featured", "Top Paid" and "Top Free".

History

The Android Market was announced on 28 August 2008 and was made available to users on 22 October 2008. Priced application support was added for U.S. users and developers in the U.S. and UK in mid-February 2009. UK users gained the ability to purchase priced applications on 13 March 2009.
On 17 March 2009, there were about 2,300 applications available for download from the Android Market, according to T-Mobile chief technical officer Cole Brodman.[2]
By December 2009, there were over 20,000 applications available for download in the Android Market.[3]
By August 2010, there were over 80,000[4] applications available for download in the Android Market, with over 1 billion application downloads.[5][6] Recent months (in 2010) have shown an ever increasing growth rate, recently (in May 2010) surpassing 10,000 additional applications per month.[7]
A report in July 2010, a company named Distimo showed that the Android Market features the highest percentage of free apps, with over 57% being free to download, double the amount of Apple Inc.'s App Store, in which only 28% of apps are free. Other competitors, such as Nokia's Ovi Store and Blackberry's App World had 26%, with Windows Marketplace only having 22%.[8]
In December 2010, it was reported that the Market would shortly receive an update, which will, alongside some minor updates, will add content-filtering to the market, and will reduce the purchase refund window from 24/48 hours to 15 minutes. Google has said that the new update would be available to all devices running Android 1.6 or higher[9], and arrived on unlocked HTC Desires in the UK on 16th December.
On December 31, 2010 the Android market reached the 200,000 app milestone. [10]

Priced applications

Developers of software (apps) receive 70% of the application price, with the remaining 30% distributed among carriers (if authorized to receive a fee for applications purchased through their network) and payment processors.[11] Revenue earned from the Android Market is paid to developers via Google Checkout merchant accounts. T-Mobile, the first carrier with an Android device, recently updated the market to allow Google to directly bill app purchases to a customer's cell phone account that show up as a charge on the bill.

Availability for users

Users outside the countries/regions listed below only have access to free applications through Android Market. Paid applications are currently available to Android Market users in following countries:
Country Users can purchase apps[12] Developers can sell apps[13]
 Argentina Yes Yes
 Australia Yes Yes
 Austria Yes (except MVNO) Yes
 Czech Republic Yes No
 Canada Yes Yes
 Belgium Yes Yes
 Brazil Yes Yes
 Denmark Yes Yes
 Finland Yes Yes
 France Yes Yes
 Germany Yes Yes
 Hong Kong Yes Yes
 India Yes No
 Ireland Yes Yes
 Israel Yes Yes
 Italy Yes Yes
 Japan Yes Yes
 Mexico Yes Yes
 Netherlands Yes Yes
 New Zealand Yes Yes
 Norway Yes Yes
 Pakistan Yes No
 Poland Yes No
 Portugal Yes Yes
 Russia Yes Yes
 Singapore Yes Yes
 Sweden Yes Yes
 Switzerland Yes Yes
 Taiwan Yes Yes
 South Korea Yes Yes
 Spain Yes Yes
 United Kingdom Yes Yes
 United States Yes Yes
Users reported problems with at least several mobile virtual network operators (MVNOs) in some of the countries listed above whose subscribers can't access priced applications.
  • Simyo and Jazztel Móvil,[14]  Spain.
As of 30 April 2010, these problems were fixed, and users of BOB and Jazztel have reported[15] the market showing the paid downloads too.

Availability for developers

Early on, only developers in the U.S. and UK were able to publish priced applications. In an email to Android Market developers on 2 April 2009, Google wrote: "... we are hard at work to enable developers in Germany, Austria, Netherlands, France, and Spain to offer priced applications in the coming weeks. Once merchant support for priced apps are live in these countries, we will announce our plans for launching support for developers in additional geographies."
This was partly realized and, for the time being, developers from Austria, France, Germany, Netherlands, Spain, UK and the U.S. can sell priced applications on the Android Market.[13]
Unlike with the iPhone, there is no requirement that Android applications be acquired from Android Market. Android applications may be obtained from any source including a developer's own website or from any of the 3rd party alternatives to Market which exist and can be installed on Android devices alongside Market.

Banned applications

On 31 March 2009, Google pulled all tethering applications from the Android Market.[16] Google later restored the applications for Android Market users, except those inside the T-Mobile USA network:[17]
On Monday, several applications that enable tethering were removed from the Android Market catalog because they were in violation of T-Mobile's terms of service in the US. Based on Android's Developer Distribution Agreement (section 7.2), we remove applications from the Android Market catalog that violate the terms of service of a carrier or manufacturer. We inadvertently unpublished the applications for all carriers, and today we have corrected the problem so that all Android Market users outside the T-Mobile US network will now have access to the applications. We have notified the affected developers.[17]
As of 20 May 2010, PDAnet, Easy Tether and Proxoid were all available in the U.S. market for T-mobile users.

Implementation details

The applications themselves are self-contained Android Package files. The Android Market does not install applications itself, rather it asks the phone's PackageManagerService to install them. The package manager can be seen directly if the user tries to download an APK file direct to their phone. Applications can be installed to the phone's internal storage, and can also be installed to the owner's external storage card under certain conditions.[18]

Application security

Android devices can run applications written by third party developers and distributed through the Android Market or one of several other application stores. Once they have signed up, developers can make their applications available immediately, without a lengthy approval process.
When an application is installed, Android displays all required permissions. At that point the user can decide whether or not to install the application. The user may decide not to install an application whose permission requirements seem excessive or unnecessary. A game may need to enable vibration, for example, but should not need to read messages or access the phonebook.
App permissions include things like:
  • Accessing the Internet
  • Making phone calls
  • Sending SMS messages
  • Reading and writing to the installed memory card
  • Accessing a user's address book data
While there have only been a few malware attacks in the wild, the possibility exists, so security software companies have been developing applications to help ensure the security of Android devices. SMobile Systems, one such manufacturer, makes the claim that 20% of the apps in the Android Market request permissions that could be used for malicious purposes. They also state that five percent of the apps can make phone calls without the user's intervention.[19][20][21] Note that they are not claiming that the apps actually are malicious, just that the possibility exists.

Known issues

As of May 2010, a widespread issue has been reported by hundreds of users which inhibits their ability to download apps from the marketplace. Some user issues are related to the migration of UK users from googlemail.com addresses to gmail.com,[22] but the majority are still unresolved, despite a number of suggested fixes.[when?] The two most popular questions on Android technical help relate to the issue, with hundreds of unanswered queries.[23][not in citation given]
Hundreds of users across multiple networks have experienced the market place app disappearing after updating to Android 2.2. So far, the only solution Google has offered is to hard reset your phone. However, doing so will delete contacts, text messages and apps from the phone. One other way that can work is to make sure the Google Chat app on the device is signed in to your googlemail/gmail account - and then the Market Place app should allow downloads (OS 2.2), may be fixed in later versions.[citation needed]

 

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Minggu, 02 Januari 2011

Low-pass filter

A low-pass filter is a filter that passes low-frequency signals but attenuates (reduces the amplitude of) signals with frequencies higher than the cutoff frequency. The actual amount of attenuation for each frequency varies from filter to filter. It is sometimes called a high-cut filter, or treble cut filter when used in audio applications. A low-pass filter is the opposite of a high-pass filter, and a band-pass filter is a combination of a low-pass and a high-pass.
Low-pass filters exist in many different forms, including electronic circuits (such as a hiss filter used in audio), digital filters for smoothing sets of data, acoustic barriers, blurring of images, and so on. The moving average operation used in fields such as finance is a particular kind of low-pass filter, and can be analyzed with the same signal processing techniques as are used for other low-pass filters. Low-pass filters provide a smoother form of a signal, removing the short-term fluctuations, and leaving the longer-term trend

Examples of low-pass filters

Acoustic

A stiff physical barrier tends to reflect higher sound frequencies, and so acts as a low-pass filter for transmitting sound. When music is playing in another room, the low notes are easily heard, while the high notes are attenuated.

Electronic

In an electronic low-pass RC filter for voltage signals, high frequencies contained in the input signal are attenuated but the filter has little attenuation below its cutoff frequency which is determined by its RC time constant.
For current signals, a similar circuit using a resistor and capacitor in parallel works in a similar manner. See current divider discussed in more detail below.
Electronic low-pass filters are used to drive subwoofers and other types of loudspeakers, to block high pitches that they can't efficiently broadcast.
Radio transmitters use low-pass filters to block harmonic emissions which might cause interference with other communications.
The tone knob found on many electric guitars is a low-pass filter used to reduce the amount of treble in the sound.
An integrator is another example of a single time constant low-pass filter.[1]
Telephone lines fitted with DSL splitters use low-pass and high-pass filters to separate DSL and POTS signals sharing the same pair of wires.
Low-pass filters also play a significant role in the sculpting of sound for electronic music as created by analogue synthesisers. See subtractive synthesis.

Ideal and real filters

The sinc function, the impulse response of an ideal low-pass filter.
An ideal low-pass filter completely eliminates all frequencies above the cutoff frequency while passing those below unchanged: its frequency response is a rectangular function, and is a brick-wall filter. The transition region present in practical filters does not exist in an ideal filter. An ideal low-pass filter can be realized mathematically (theoretically) by multiplying a signal by the rectangular function in the frequency domain or, equivalently, convolution with its impulse response, a sinc function, in the time domain.
However, the ideal filter is impossible to realize without also having signals of infinite extent in time, and so generally needs to be approximated for real ongoing signals, because the sinc function's support region extends to all past and future times. The filter would therefore need to have infinite delay, or knowledge of the infinite future and past, in order to perform the convolution. It is effectively realizable for pre-recorded digital signals by assuming extensions of zero into the past and future, or more typically by making the signal repetitive and using Fourier analysis.
Real filters for real-time applications approximate the ideal filter by truncating and windowing the infinite impulse response to make a finite impulse response; applying that filter requires delaying the signal for a moderate period of time, allowing the computation to "see" a little bit into the future. This delay is manifested as phase shift. Greater accuracy in approximation requires a longer delay.
An ideal low-pass filter results in ringing artifacts via the Gibbs phenomenon. These can be reduced or worsened by choice of windowing function, and the design and choice of real filters involves understanding and minimizing these artifacts. For example, "simple truncation [of sinc] causes severe ringing artifacts," in signal reconstruction, and to reduce these artifacts one uses window functions "which drop off more smoothly at the edges."[2]
The Whittaker–Shannon interpolation formula describes how to use a perfect low-pass filter to reconstruct a continuous signal from a sampled digital signal. Real digital-to-analog converters use real filter approximations.

Continuous-time low-pass filters

The gain-magnitude frequency response of a first-order (one-pole) low-pass filter. Power gain is shown in decibels (i.e., a 3 dB decline reflects an additional half-power attenuation). Angular frequency is shown on a logarithmic scale in units of radians per second.
There are many different types of filter circuits, with different responses to changing frequency. The frequency response of a filter is generally represented using a Bode plot, and the filter is characterized by its cutoff frequency and rate of frequency rolloff. In all cases, at the cutoff frequency, the filter attenuates the input power by half or 3 dB. So the order of the filter determines the amount of additional attenuation for frequencies higher than the cutoff frequency.
  • A first-order filter, for example, will reduce the signal amplitude by half (so power reduces by 6 dB) every time the frequency doubles (goes up one octave); more precisely, the power rolloff approaches 20 dB per decade in the limit of high frequency. The magnitude Bode plot for a first-order filter looks like a horizontal line below the cutoff frequency, and a diagonal line above the cutoff frequency. There is also a "knee curve" at the boundary between the two, which smoothly transitions between the two straight line regions. If the transfer function of a first-order low-pass filter has a zero as well as a pole, the Bode plot will flatten out again, at some maximum attenuation of high frequencies; such an effect is caused for example by a little bit of the input leaking around the one-pole filter; this one-pole–one-zero filter is still a first-order low-pass. See Pole–zero plot and RC circuit.
  • A second-order filter attenuates higher frequencies more steeply. The Bode plot for this type of filter resembles that of a first-order filter, except that it falls off more quickly. For example, a second-order Butterworth filter will reduce the signal amplitude to one fourth its original level every time the frequency doubles (so power decreases by 12 dB per octave, or 40 dB per decade). Other all-pole second-order filters may roll off at different rates initially depending on their Q factor, but approach the same final rate of 12 dB per octave; as with the first-order filters, zeroes in the transfer function can change the high-frequency asymptote. See RLC circuit.
  • Third- and higher-order filters are defined similarly. In general, the final rate of power rolloff for an order-n all-pole filter is 6n dB per octave (i.e., 20n dB per decade).
On any Butterworth filter, if one extends the horizontal line to the right and the diagonal line to the upper-left (the asymptotes of the function), they will intersect at exactly the "cutoff frequency". The frequency response at the cutoff frequency in a first-order filter is 3 dB below the horizontal line. The various types of filters – Butterworth filter, Chebyshev filter, Bessel filter, etc. – all have different-looking "knee curves". Many second-order filters are designed to have "peaking" or resonance, causing their frequency response at the cutoff frequency to be above the horizontal line. See electronic filter for other types.
The meanings of 'low' and 'high' – that is, the cutoff frequency – depend on the characteristics of the filter. The term "low-pass filter" merely refers to the shape of the filter's response; a high-pass filter could be built that cuts off at a lower frequency than any low-pass filter – it is their responses that set them apart. Electronic circuits can be devised for any desired frequency range, right up through microwave frequencies (above 1 GHz) and higher.

Laplace notation

Continuous-time filters can also be described in terms of the Laplace transform of their impulse response in a way that allows all of the characteristics of the filter to be easily analyzed by considering the pattern of poles and zeros of the Laplace transform in the complex plane (in discrete time, one can similarly consider the Z-transform of the impulse response).
For example, a first-order low-pass filter can be described in Laplace notation as
\frac{\text{Output}}{\text{Input}} = K \frac{1}{1 + s \tau}
where s is the Laplace transform variable, τ is the filter time constant, and K is the filter passband gain.

Electronic low-pass filters

Passive electronic realization

Passive, first order low-pass RC filter
One simple electrical circuit that will serve as a low-pass filter consists of a resistor in series with a load, and a capacitor in parallel with the load. The capacitor exhibits reactance, and blocks low-frequency signals, causing them to go through the load instead. At higher frequencies the reactance drops, and the capacitor effectively functions as a short circuit. The combination of resistance and capacitance gives you the time constant of the filter τ = RC (represented by the Greek letter tau). The break frequency, also called the turnover frequency or cutoff frequency (in hertz), is determined by the time constant:
f_\mathrm{c} = {1 \over 2 \pi \tau } = {1 \over 2 \pi R C}
or equivalently (in radians per second):
\omega_\mathrm{c} = {1 \over \tau} = { 1 \over R C}.
One way to understand this circuit is to focus on the time the capacitor takes to charge. It takes time to charge or discharge the capacitor through that resistor:
  • At low frequencies, there is plenty of time for the capacitor to charge up to practically the same voltage as the input voltage.
  • At high frequencies, the capacitor only has time to charge up a small amount before the input switches direction. The output goes up and down only a small fraction of the amount the input goes up and down. At double the frequency, there's only time for it to charge up half the amount.
Another way to understand this circuit is with the idea of reactance at a particular frequency:
  • Since DC cannot flow through the capacitor, DC input must "flow out" the path marked Vout (analogous to removing the capacitor).
  • Since AC flows very well through the capacitor — almost as well as it flows through solid wire — AC input "flows out" through the capacitor, effectively short circuiting to ground (analogous to replacing the capacitor with just a wire).
The capacitor is not an "on/off" object (like the block or pass fluidic explanation above). The capacitor will variably act between these two extremes. It is the Bode plot and frequency response that show this variability.

Active electronic realization

An active low-pass filter
Another type of electrical circuit is an active low-pass filter.
In the operational amplifier circuit shown in the figure, the cutoff frequency (in hertz) is defined as:
f_{\text{c}} = \frac{1}{2 \pi R_2 C}
or equivalently (in radians per second):
\omega_{\text{c}} = \frac{1}{R_2 C}.
The gain in the passband is −R2/R1, and the stopband drops off at −6 dB per octave as it is a first-order filter.
Sometimes, a simple gain amplifier (as opposed to the very-high-gain operational amplifier) is turned into a low-pass filter by simply adding a feedback capacitor C. This feedback decreases the frequency response at high frequencies via the Miller effect, and helps to avoid oscillation in the amplifier. For example, an audio amplifier can be made into a low-pass filter with cutoff frequency 100 kHz to reduce gain at frequencies which would otherwise oscillate. Since the audio band (what we can hear) only goes up to 20 kHz or so, the frequencies of interest fall entirely in the passband, and the amplifier behaves the same way as far as audio is concerned.

Discrete-time realization

For another method of conversion from continuous- to discrete-time, see Bilinear transform.
The effect of a low-pass filter can be simulated on a computer by analyzing its behavior in the time domain, and then discretizing the model.
A simple low-pass RC filter
From the circuit diagram to the right, according to Kirchoff's Laws and the definition of capacitance:
v_{\text{in}}(t) - v_{\text{out}}(t) = R \; i(t)




(V)
Q_c(t) = C \, v_{\text{out}}(t)




(Q)
i(t) = \frac{\operatorname{d} Q_c}{\operatorname{d} t} \, ,




(I)
where Qc(t) is the charge stored in the capacitor at time t. Substituting equation Q into equation I gives i(t) = C \frac{\operatorname{d}v_{\text{out}}}{\operatorname{d}t}, which can be substituted into equation V so that:
v_{\text{in}}(t) - v_{\text{out}}(t) = RC \frac{\operatorname{d}v_{\text{out}}}{\operatorname{d}t}.\,
This equation can be discretized. For simplicity, assume that samples of the input and output are taken at evenly-spaced points in time separated by ΔT time. Let the samples of vin be represented by the sequence (x_1, x_2, \ldots, x_n), and let vout be represented by the sequence (y_1, y_2, \ldots, y_n) which correspond to the same points in time. Making these substitutions:
x_i - y_i = RC \, \frac{y_{i}-y_{i-1}}{\Delta_T}.\,
And rearranging terms gives the recurrence relation
y_i = \overbrace{x_i \left( \frac{\Delta_T}{RC + \Delta_T} \right)}^{\text{Input contribution}} + \overbrace{y_{i-1} \left( \frac{RC}{RC + \Delta_T} \right)}^{\text{Inertia from previous output}}.
That is, this discrete-time implementation of a simple RC low-pass filter is the exponentially-weighted moving average
y_i = \alpha x_i + (1 - \alpha) y_{i-1} \qquad \text{where} \qquad \alpha \triangleq \frac{\Delta_T}{RC + \Delta_T}.\,
By definition, the smoothing factor 0 \leq \alpha \leq 1. The expression for α yields the equivalent time constant RC in terms of the sampling period ΔT and smoothing factor α:
RC = \Delta_T \left( \frac{1 - \alpha}{\alpha} \right).
If α = 0.5, then the RC time constant is equal to the sampling period. If \alpha \ll 0.5, then RC is significantly larger than the sampling interval, and \Delta_T \approx \alpha RC.

Algorithmic implementation

The filter recurrence relation provides a way to determine the output samples in terms of the input samples and the preceding output. The following pseudocode algorithm will simulate the effect of a low-pass filter on a series of digital samples:
// Return RC low-pass filter output samples, given input samples,
 // time interval dt, and time constant RC
 function lowpass(real[0..n] x, real dt, real RC)
   var real[0..n] y
   var real α := dt / (RC + dt)
   y[0] := x[0]
   for i from 1 to n
       y[i] := α * x[i] + (1-α) * y[i-1]
   return y
The loop which calculates each of the n outputs can be refactored into the equivalent:
for i from 1 to n
       y[i] := y[i-1] + α * (x[i] - y[i-1])
That is, the change from one filter output to the next is proportional to the difference between the previous output and the next input. This exponential smoothing property matches the exponential decay seen in the continuous-time system. As expected, as the time constant RC increases, the discrete-time smoothing parameter α decreases, and the output samples (y_1,y_2,\ldots,y_n) respond more slowly to a change in the input samples (x_1,x_2,\ldots,x_n) – the system will have more inertia.
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